MOTION SAMPLE BOOKLET CLASS X - Kota Coaching SAMPLE BOOKLET CLASS X ... As charge is the basis of all electrical phenomena, ... The silk cloth, which gains electrons,

MOTION SAMPLE BOOKLET CLASS X

• ELECTRICITY

• CHEMICAL REACTIONS AND EQUATIONS

• NUTRITION

• REAL NUMBER

• WORK LIFE & LEISURE

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ELECTRICITY

S.NO. TOPIC PAGE NO.

THEORY.............................................................................................. 5 – 21

SOLVED EXAMPLE ............................................................................. 22 – 29

EXERCISE - I ....................................................................................... 30 – 33

EXERCISE -II ....................................................................................... 34 – 38

CONTENTS

THEORY AND EXERCISE BOOKLET

CHEMICAL REACTIONS AND EQUATIONS


THEORY.............................................................................................. 39 – 60

SOLVED EXAMPLE ............................................................................. 61 – 70

EXERCISE - I ....................................................................................... 71 – 73

EXERCISE -II ....................................................................................... 74 – 77

NUTRITION


THEORY.............................................................................................. 78 – 86

SOLVED EXAMPLE ............................................................................. 87 – 87

EXERCISE - I ....................................................................................... 88 – 89

EXERCISE -II ....................................................................................... 90 – 90

CLASS - X

REAL NUMBERS


THEORY .............................................................................................. 91 – 92

SOLVED EXAMPLE ............................................................................. 93 – 97

EXERCISE - I ....................................................................................... 98 – 102

EXERCISE -II ....................................................................................... 103 – 103

EXERCISE -III ...................................................................................... 104 – 109

CONTENTS

THEORY AND EXERCISE BOOKLET

WORK, LIFE AND LEISURE


THEORY .............................................................................................. 110 – 117

EXERCISE - I ....................................................................................... 118 – 119

EXERCISE -II ....................................................................................... 120 – 120

Page # 5

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ELECTRICITY

ELECTRIC CHARGE

(A) Definition: Electric charge may be defined as the intrinsic property of certain fundamental particles(electron, proton, etc) due to which they produce electric and magnetic effects.

(B) Charge on a Macrobody: Excess or deficiency of electrons in a body is equal to the charge on amacrobody. A body having excess of electrons in negatively charge and a body having deficiency ofelectrons is positively charged.

From the study of atomic structure, we know that an atom consists of a central part called nucleusand around the nucleus there are a number of electrons revolving in different paths or orbits. Thenucleus contains protons and neutrons. A proton is a positively charged particle while a neutron has nocharge. Therefore, the nucleus of an atom bears a positive charge. An electron is a negatively chargedparticle having negative charge equal to the positive charge on a proton. Normally, the number ofelectrons is equal to the number of protons in an atom. Therefore, an atom is neutral as a whole; thenegative charge on electrons cancelling the positive charge on protons. This leads to the conclusionthat under ordinary conditions, a body is neutral i.e. it exhibits no charge.

When this equity or balance is disturbed by removing or supplying electrons, the body acquires a netcharge. The body will acquire a positive or negative charge depending upon whether electrons areremoved from it or added to it.

(C) Types of Electric Charge: There are two types of charges. They are:(i) Positive charge: A body having deficiency of electrons.

(ii) Negative charge: A body having excess of electrons.

(D) Charging of a Body: There are a number of methods to charge a body as:

(i) Charging by friction

(ii) Charging by conduction

(iii) Charging by induction etc.We will discuss charging by friction in detail:

Whenever two bodies (at least one non conductor) are rubbed against each other, heat is produceddue to friction present between them. Due to this heat produced, electrons in both the bodies areexcited. The body having more electron affinity attracts some of the electrons from other body. Boththe bodies develop equal and opposite charges by this method.

S.No. Positive charge Negative Charge

1 Glass Rod Silk cloth

2 Fur or woolen cloth Ebonite, Amber, Rubber rod

3 Woolen coat Plastic seat

4 Woolen carpet Rubber shoes

5 Nylon or Acetate Cloth

6 Dry hair Comb

(E) Properties of Electric Charge:

(i) Like charges repel and unlike charges attract each other.(ii) Charge is a scalar quantity.

(iii) Charge is always quantized.

(iv) Charge is conserved.

(v) Charge is always associated with mass.

ELECTRICITY

Page # 6 ELECTRICITY

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(F) Unit of Charge: The charge on an electron is so small that it is not convenient to select it the unit ofcharge. In practice, coulomb is used as the unit of charge, i.e. SI unit of charge is coulomb abbreviatedas C. One coulomb of charge is equal to the charge on 625 × 1016 electrons.

1 coulomb = charge on 625 × 1016 electrons or 6.25 × 1018 electrons

Thus, when we say that a body has a positive charge of one coulomb (i.e + 1C) it means that the bodyhas a deficit of 625 × 1016 electrons from the normal due share.

If a neutral body is made positively charged, is there any change in its mass?

Newton's Thought

ExplanationIn charging any neutral body, the mass of a body changes, though the changeis extremely small or negligible. If a neutral body is made positive, it meanselectrons are removed from it. Thus, the mass of body decreases.

STATIC AND CURRENT ELECTRICITY

(A) Static Electricity: A branch of physics which deals with the study of the electric charges at rest andtheir effects is known as electrostatic or static electricity.

(B) Current Electricity: A branch of physics which deals with the study of the electric charges in motionand their effects is known as current electricity.

ELECTRIC FIELD AND ELECTRIC POTENTIAL

(A) Electric Field: Electric field due to a given charge is defined as the space around the charge in whichelectrostatic force of attraction or repulsion due to charge can be experienced by any other charge. Ifa test charge experiences no force at a point, the electric field at that point must be zero.

Electric field intensity at any point is the strength of electric field at that point. It is defined as theforce experienced by unit positive charge placed at that point.

If F is the force acting on a test charge +q0 at any point r, then electric field intensity at this point isgiven by

0

FE

q

Electric field is a vector quantity and its S.I. unit is Newton per coulomb or N/C.

(B) Electric Potential: The electric potential at a point in an electric field is defined as the amount of workdone in moving a unit +ve charge from infinity to that point, without acceleration or without a changein K.E. against the electric force Mathematically.

WV

q

Since work is measured in joule and charge in coulomb, therefore electric potential is measured in jouleper coulomb (J/C). This unit occurs so often in our study of electricity, so it has been named as volt, inhonour of the scientist Alessandra Volta (the inventor of the voltaic cell).

1 joule1 Volt1 coulomb

Potential is a scalar quantity, therefore it is added algebraically. For a positively charged body potentialis positive and for a negatively charged body potential is negative.

Page # 7


ELECTRICITY

(C) Electric Potential Difference: Consider a charge Q placed at a point P. Let A and B be two otherpoints (B being closer to A) as shown in figure.

P

Q B A q

From infinity

If a charge q is brought from infinity to A, work WA will be done.

The potential at A will then be, A

AW

Vq

If charge q is brought from infinity to B, the work done will be WB.

The potential at B will then be, B

BW

Vq

The quantity VB – VA is called the potential difference between points A and B in the electric field ofcharge Q. Mathematically we have,

B AB A

W WV V

q q

Electric potential difference is also measured in volt.

ELECTRICITY

The source of all electricity is charge. As charge is the basis of all electrical phenomena, we need toknow the amount of charge on a body. It is measured in coulombs. The coulomb is the SI unit of chargeand its symbol is C.

Matter is generally made of protons, electrons and neutrons. Each proton carries a charge of1.6 × 10–19 coulomb, and each electron carries an equal negative charge. Neutrons do not carry anynet charge. Normally, a body has equal number of protons and electrons, and is therefore, electricallyneutral. In certain situations, the balance of charges in a body is disturbed.For example:- when a glass rod is rubbed with a silk cloth, some electrons get transferred from theglass rod to the silk. The silk cloth, which gains electrons, becomes negatively charged. And the glassrod, which is left with more protons than electrons, becomes positively charged.Charged particles or objects can exert forces on each other. While like (similar) charges repel each other,unlike charges attract. Another important thing about charged particles is that they can flow, i.e., theycan move in a particular direction. This flow of charged particles is called an electric current. Chargedparticles such as electrons are present in all substances. But they do not flow on their own. For flow ofcharges, there has to be a potential difference.

POTENTIAL DIFFERENCE AND THE FLOW OF CHARGE

q

BA

Charges

The potential difference between two points A and B is the work done per unit charge in taking acharge from B to A. We express this mathematically as

A BWV V – Vq

Here, V is the potential difference between the points A and B, and VA and VB are the potentials atthese points. The potential at infinity is chosen as zero.



If B be the reference point, the potential at B is VB = O. From Equation, the potential at A isVA = W/q. So, the potential at a point is the work done per unit charge in taking a charge to that pointfrom a chosen reference point. Equation may also be written as

W= qV.The work done on the charge q is stored as the electric potential energy (U) of the group of charges.So,

U = qV

UNIT OF POTENTIAL DIFFERENCEThe unit of potential difference (and potential) is the volt, whose symbol is V. One volt is the potentialdifference between two points in a current carrying conductor when 1 joule of work is done to move acharge of 1 coulomb from one point to the other.

–11 Joule1 volt or 1 V 1 JC

1 Coulomb

The potential difference between two points is sometimes also called the voltage.

FLOW OF CHARGE

Consider two identical metallic spheres P and N, carrying equal amounts of positive and negative chargesrespectively. A positive charge is to be taken from B to A. It is attracted by the negatively chargedsphere N and repelled by the positively charged sphere P. So, to move the charge towards A, one has toapply a force on it towards the left. Thus, the work done is positive. Hence, the potential difference VA

– VB is positive. This means VA > VB'

As one moves towards P, the work done increases; so, the potential increases. And on moving towardsN, the potential decreases. So, the potential of P is higher than that of N. In general, the potential ofa positively charged body is taken as higher than that of a negatively charged body.

+ –

P N––

––– –

–

+B

Repulsion Attraction

A+++ +

+++

What happens when a free-to-move charge is placed between the spheres? A positive charge willmove towards the negatively charged sphere. And a negative charge will move towards the positivelycharged sphere. That is, a free positive charge moves towards lower potential. And a free negativecharge moves towards higher potential.If the two spheres are connected by a metal wire, electrons from the negatively charged sphere (at alower potential) will flow to the positively charged sphere (at a higher potential). Eventually, the flowof electrons causes the charges on the spheres to become balanced. When that happens, the spheresno longer carry a net charge, and therefore, have equal potential. So, the flow of electrons stops. Sowe can say that a potential difference causes charges to flow.

+

–––

–

Electrons–––

Higher potential

Lowerpotential

(a) (b)

+ ++ +

++

Page # 9


ELECTRICITY

A CELL PROVIDES A CONSTANT POTENTIAL DIFFERENCE

The potential difference provided by things like charged spheres reduces to zero quickly once chargesstart to flow. So, we have to use cells to provide constant potential difference for a long time. Cellshave chemicals inside. Reactions in the cell cause positive and negative charges to gather separately.This creates a potential difference between the terminals of the cell. The terminal at a higher potentialis called the positive terminal and the one at a lower potential is called the negative terminal.

The cells that we commonly use are called dry cells (Figure). In a common dry cell, the small metalliccap at one end is the positive terminal, while the flat metallic plate at the other end is the negativeterminal. It provides a potential difference of 1.5 V. A cell is represented by the symbol shown in fig(b). The larger line represents the positive terminal, while the shorter line represents the negativeterminal.

A COMBINATION OF CELLS IS CALLED A BATTERY

Quite often, multiple cells are combined to get a potential difference that is higher than that of a singlecell. For example, we connect two 1.5V cells to get a potential difference of 3V (Figure (c)) This isshown using symbols in Figure (d).

Positiveterminal

Negativeterminal

1.5V 1.5V

A battery of two cells to provide 3 volts

(a) (b) (c) (d)

+ +– –

ELECTRIC CURRENT

Consider a metallic wire ACB connected across a cell of potential difference V. Since the end A isconnected to the positive terminal, it is at a higher potential than the end B. In metals, some electronsare loosely bound to the atoms, and can move within it. These are called free electrons. In the metallicwire, these electrons (negative charges) move from the low-potential side B to the high-potential sideA. After reaching A, they enter the cell. The chemical reactions in the cell drive these electrons to thenegative terminal. From there, they re-enter the wire at the end B. Thus, there is a continuous flow ofelectrons in the wire from B to C to A. We say that there is an electric current in the wire. In a metal,the flow of negative charges constitutes the current.

A B

C

Direction of current

Current in a wire connected to a cellAn electric current can also be a flow of positive charges. So, a flow of charge is called an electriccurrent.By convention, the direction of current is taken as the direction of flow of positive charges.Thus, the direction of current is opposite to the direction of flow of negative charges. So, when awire is connected to a cell, the current in the wire is from the positive-terminal end to thenegative-terminal end.



MEASUREMENT OF CURRENT

The charge passing per unit time through a given place(area) is the magnitude of the electric currentat that place. Thus,

Qi

tHere Q is the charge that passes through a place in time t.

Unit of current From Equation, we find that current is charge divided by time. The SI unit of charge isthe coulomb and that of time is the second. The SI unit of current, therefore, is coulomb / second.This unit is called the ampere, whose symbol is A.

Thus, if one coulomb of charge passes through a place in one second, the current there is 1 ampere.

CONDUCTORS AND INSULATORS

Materials that conduct electricity easily are called good conductors or simply, conductors. And, materialsthat do not conduct electricity easily are called insulators.

All metals conduct electricity because they have some loosely bound free electrons, which flow whena potential difference is applied. However, some metals conduct electricity better than others. Silver isthe best conductor. But because of the high cost of silver, electric wires are made of copper, or in somecases aluminium.

Most nonmetallic solids do not conduct electricity. Although diamond and graphite are both forms of carbon(a nonmetal), graphite is a conductor while diamond is an insulator. Insulators do not conduct electricitybecause their electrons are tightly bound to the atoms. Rubber, plastics, wood, glass and porcelain aresome examples of insulators. Insulators have many uses. For example, they are used as protective coverson electric wires and electrician's tools.

Certain liquids also conduct electricity. While distilled water is an insulator, addition of certain salts,acids or bases allows it to conduct electricity. Under normal circumstances, gases do not conductelectricity.

ELECTRIC CIRCUITS AND MEASURING INSTRUMENTS

A closed path in which a current can flow is called an electric circuit. An electric circuit may haveone or more electric elements such as bulbs (or lamps), cells, switches (or plug keys), metal wires, etc.Each element of a circuit has a specific function to play. For example, wires can be used to connectone element to the next. And a plug key or a switch can be used to either complete or break the closedpath, thereby starting or stopping the current in the circuit.

Some common circuit elements and their symbols are shown in Figure.

Bulb (lamp)

Fuse

Plug key (OFF)

Plug key (ON)

Switch (OFF)

Switch (ON)

Resistor

Variable Resistor(rheostat)

Unconnectedconductor

Connectedconductors

Ammeter

Voltmeter

+

+

Fig. Some symbols used in circuit diagrams

COMMON MEASURING INSTRUMENTS

The electric current in a circuit is measured by an instrument called the ammeter, and thepotential difference between two points in it is measured by a voltmeter (in voltage stabilizers).In these meters, a needle moving over a graduated scale gives the value of the measured quantity.Each meter has two terminals. The terminal marked '+' is connected by a wire to the higher-potentialside of a circuit, while the terminal marked '–' is connected to the lower-potential side.

Page # 11


ELECTRICITY

USING AN AMMETER TO MEASURE CURRENTTo measure the current through an element of a circuit, an ammeter is connected in such a way thatthe current flowing through it also flows through the element. Such a connection is called a seriesconnection. In Figure, the current i flowing through the lamp also flows through the ammeter. Thereading of the ammeter gives the current through the lamp. Note that if the ammeter is removed, therewill be a gap, and the current through the circuit will stop.

+A

–i

Ammeter in a circuitTwo or more electric elements are said to be connected in series if the current flowing throughone also flows through the rest.An ammeter is always connected in series in a circuit.

USING A VOLTMETER TO MEASURE POTENTIAL DIFFERENCEFigure shows a circuit that has two lamps connected to a cell. We want to measure the potentialdifference across the lamp L2, i.e., between the points A and B. As A is on the side of the positiveterminal of the cell, its potential is higher than that of B. So, the '+' terminal of the voltmeter isconnected to A, and the '–' terminal, to B. The reading of the voltmeter gives the potential differenceacross L2. The current flowing through the voltmeter is different from those flowing through the otherelements of the circuit. Also, even if the voltmeter is removed, the current continues to flow in thecircuit. Note that the potential difference across L2 and the voltmeter is the same. Such a connectionis called a parallel connection.

+V

–i2

i i1

L1 L2A B

Voltmeter in a circuitTwo or more electric elements are said to be connected in parallel if the same potential differenceexists across them.

OHM'S LAW

The electric current through a metallic element or wire is directly proportional to the potential differenceapplied between its ends, provided the temperature remains constant.If a potential difference V is applied to an element and a current i passes through it,

i V

or 1i=R

V

Thus Ohm's Law V = iR

1 volt1ohm

1 ampere

i (A)

V (volt)Here R is a constant for the given element (metallic wire) at a given temperature and is called itsresistance. It is the property of a conductor to resist the flow of charges through it.



RESISTANCE

From equation,ViR

So, for a given potential difference,1R

i

Thus, for a given potential difference, the current is inversely proportional to the resistance. Thehigher is the resistance, the lower is the current. If the resistance is doubled, the current is halved.Good conductors have low resistance, while insulators have very high resistance.UNIT OF RESISTANCE

Potential difference is measured in volts, and current is measured in amperes. From Equation, R = V/i. So, the unit of resistance is volt/ampere. This unit is called the ohm, and its symbol is . We candefine one ohm as follows.

If a potential difference of 1 volt is applied across an element, and a current of 1 ampere passesthrough it, the resistance of the element is called 1 ohm.

ON WHAT DOES RESISTANCE DEPEND ?

The resistance of the conductor depends on:

(i) on its length

(ii) on its area of cross-section

(iii) on the nature of its material

(iv) Resistance depends on temperature (resistance increases with increase in temperature)

Resistance of a uniform metallic conductor is directly proportional to its length ( ) and inverselyproportional to the area of cross-section (A).

R and R 1A

Combining eqs. we get RA

or RA

Where (rho) is a constant of proportionality and is called electrical resistivity of the material of the

conductor.

RESISTIVITY ( ) : Here, is a constant for a given material at a given temperature. It is called the

resistivity of the material. the resistivity of a material is the resistance per unit length of a unit cross

section of the material. The SI unit of a material depends on its temperature. For metals and alloys ofmetals, the resistivity increases with rise in temperature. The SI unit of resistivity is m.

Silver 1.6 × 10–8

Copper 1.7 × 10–8

Aluminium 2.8 × 10–8

Tungsten 5.8 × 10–8

Iron 9.7 × 10–8

Manganin 48.2 × 10–8

Nichrome 100 × 10–8

Germanium 4.7 × 10–3

Silicon 2.5 × 103

Diamond 5 × 1012

Fused quartz 1016 – 1019

Metals

Alloys

Semiconductors

Insulators

Material Resistivity

Page # 13


ELECTRICITY

Two materials have different resistivities. Two wires of the same length are made, one from each of the materials. Is it possible for each wire to have the same resistance?

Newton's Thought

ExplanationTwo wires of the same length are made, one from of the materials. The resistance

ARof a wire is given by,

Across-sectional areas of the wires are chosen so that the ratio is the same for

each. That is

1

2

1

2

22

11 A

Aor

AAThis is the condition for each wire of different materials to have the sameresistance when they have same length.

AA R1 R2 R3 B

V1 V2 V3

VA series combination of resistors

SERIES AND PARALLEL CONNECTIONS OF RESISTORS

A conducting material (e.g., a wire) of a particular resistance meant for use in a circuit is called aresistor. A resistor is sometimes simply referred to as a resistance. It is represented by the symbol

. Two or more resistors can be connected in series, in parallel or in a manner that is a combinationof these two.

1. SERIES CONNECTION OF RESISTORSTwo or more resistors are said to be connected in series if the current flowing through one also flowsthrough the rest.The total potential difference across the combination of resistors connected in series is equal to thesum of the potential differences across the individual resistors.

1 2 3V V V V

EQUIVALENT RESISTANCE IN SERIES CONNECTIONFigure (a) shows three resistors of resistances R1, R2 and R3 connected in series. The cell connectedacross the combination maintains a potential difference V across the combination. The current throughthe cell is i. The same current i flows through each resistor.Let us replace the combination of resistors by a single resistor R

eq such that the current does not

change, i.e., it remains i. This resistance is called the equivalent resistance of the combination,and its value is given by Ohm's law as Req = V/iThus V = iReq.

(a) (b)



The potential differences V1 , V2 and V3 across the resistors R1 , R2 and R3 respectively are given by

Ohm's law as : V1 = iR1 , V2 = iR2 , V3 = iR3

Since the resistors are in series, V = V1 + V2 + V3

Substituting the values of the potential differences in the above equation,

iReq = iR1 + iR2 + iR3

or iReq =i(R1 +R2 +R3)

or eq 1 2 3R = R + R + R

Similarly, for n resistors connected in series,

Equivalent resistance of resistors in series : e q 1 2 3 nR = R + R + R + ... . . + R

2. PARALLEL CONNECTION OF RESISTORS

The total current flowing into the combination is equal to the sum of the currents passing through the

individual resistors.

1 2 3i i i i

If resistors are connected in such a way that the same potential difference gets applied to each of

them, they are said to be connected in parallel.

EQUIVALENT RESISTANCE IN PARALLEL CONNECTION

Figure (a) shows three resistors of resistances R1, R2 and R3 connected in parallel across the points A

and B. The cell connected across these two points maintains a potential difference V across each

resistor. The current through the cell is i. It gets divided at A into three parts i1, i2 and i3, which flow

through R1, R2 and R3 respectively.

(a) (b)

Req

i i

R1

R2

R3

i2i1

i3

A B

i

V V

Let us replace the combination of resistors by an equivalent resistor Req

such that the current i in the

circuit does not change (Fig). The equivalent resistance is given by Ohm's law as Req = V/i.

Thus,

eq

Vi=R

The currents i1 , i2 and i3 through the resistors R1, R2 and R3 respectively are given by Ohm's law as

1 2 31 2 3

V V Vi = , i = , i =R R R

Since the resistors are in parallel,

i = i1 + i2 + i3

Page # 15


ELECTRICITY

Substituting the values of the currents in the above equation,

eq 1 2 3

V V V V= + +R R R R

or

eq 1 2 3

1 1 1 1= + +R R R R

Similarly, if there are n resistors connected in parallel, their equivalent resistance Req is given by

Equivalent Resistance of resistors in parallel : eq 1 2 n

1 1 1 1= + +.......+

R R R R

For two resistances R1 and R2 connected in parallel,

1 2

1 2 1 2

1 1 1 R + R= + =R R R R R

or

R 1 2

1 2

R RR +R

The equivalent resistance in a parallel connection is less than each of the resistances.

When a resistance is joined parallel to a comparatively smaller resistance, the equivalent resistance is

very close to the value of the smaller resistance.

NOTE : If a resistor connected in series with others is removed or fails, the current through each

resistor becomes zero. On the other hand, if a resistor connected in parallel with others fails or isremoved, the current continues to flow through the other resistors.

DISTRIBUTION OF CURRENT IN TWO RESISTORS IN PARALLEL

Consider the circuit in fig. The resistors R1 and R2 are connected in parallel. The current i gets

distributed in the two resistors.

i = i1 + i2 .....(i)

Applying Ohm's law to the resistor R1

VA – VB =R1i1· .....(ii)

And applying Ohm's law to the resistor R2

VA – VB = R2i2 .... (iii)

From (ii) and (iii), R1i1 = R

2i2 or 1

2 12

Ri iR

Substituting for i2 in (i), we have

i = i1 + 1 1 1 2

1 1 12 2 2

R R R + Ri = i 1 + = iR R R

or 2

11 2

Ri = iR + R

R1i1

A B

i

R2i2



Similarly,

12

1 2

Ri = iR + R

Thus,1 2

2 1

i R=i R

The current through each branch in a parallel combination of resistors is inversely proportional to its

resistance.

Figure shows a combination of four identical bulbs joined with a battery. Compare the brightness of the bulbs shown. What happens if bulb A fails, so that it cannot conduct current? What happens if bulb C fails? What happens if bulb D fails?

Newton's Thought

Explanation

Bulbs A and B are connected in series across the emf of th battery, whereasbulb C is connected by itself across the battery. This means the voltagedrop across C has the same magnitude as the battery voltage, whereas thissame voltage is split between bulbs A and B. As a result, bulb C will glowmore brightly than either of bulbs A and B, which will glow equally brightly.bulb D has a wire connected across it i.e., a short circuit, so that potentialdifference across bulb D is zero and it doesn't glow. If bulb A fails, B goesout, but bulb C will glow. If bulb C fails, there is no effect on the other bulbs.If bulb D fails we cannot detect this event, because bulb D was not glowinginitially; also, there is no effect on the other bulbs.

A B

DC

DEVICES IN SERIES AND PARALLEL

You must have seen tiny bulbs strung together for decorating buildings during festivals like Diwali, andoccasions like marriages, etc. These bulbs are connected in series, and the mains voltage is applied tothe combination. The potential difference (V) of the mains gets divided across the bulbs (V = V

1 + V

2 +

V3 + ... ). So, a small potential difference exists across each bulb, close to that required to make thebulb work. However, the same current flows through all the bulbs. So, if one bulb goes bad, the currentthrough it stops, and this stops the current through the rest of the bulbs as well. To make the chain oflights work, we have to find and replace the defective bulb. This problem does not occur with the lightsin our house. That is because in houses, lights, fans, etc., are connected in parallel. In parallelconnection, the same mains voltage gets applied to each device, but the current through each isdifferent. If one of them goes bad, the current in the other branches of the parallel connection doesnot stop. Another advantage of parallel connection is that, unlike series connection, each device candraw a different current, as per its requirement.

Page # 17


ELECTRICITY

HEATING EFFECT OF ELECTRIC CURRENT

When an electric current passes through a bulb, the filament gets so hot that it glows and emits light.When a current passes through the filament of an electric iron, the iron becomes very hot. Thisincrease in temperature is due to what is called 'the heat produced due to current'.Suppose a resistorR is connected to a cell. The cell maintains a potential difference V across the resistor, driving acurrent i through it.

So, V = iR ......(i)R

i

V

The current through the resistor is actually a flow of negative charges (electrons). Inside the cell, thenegative charges flow from the positive to the negative terminal. The cell does work = QV to take acharge through the potential difference V between its terminals. This increases the energy of thecharge by QV. This increased energy gets converted to heat in the resistor. So, the energy appearingas heat is given by

U = QV ......(ii)

The charge that passes through the wire in time t is

Q =it. ......(iii)

Using (i), (ii) and (iii), we find that the heat produced in the wire in time t is

U =QV = (it) (iR) =i2 Rt.

From Equation the heat produced is proportional to the square of the current, if R and t remainconstant. So, if the current passing for a given time through a given resistance is doubled, the heatproduced becomes four times. Similarly, for a given i and t, the heat produced is proportional to R. Ifthe same current i passes through two resistances in a given time, more heat will be produced in thelarger resistance. The heat produced can also be written as.

U = i2Rt =2V Rt

R

or2V

U= tR

For a given V and t, the heat produced is inversely proportional to R. So, if the same potentialdifference is applied across two resistances, more heat will be produced in the smaller resistance.

We have seen above that the increased energy of a charge gets converted to heat in the resistor. Theincrease in energy comes from the work done by the cell. This uses up the chemical energy of the cell.So, the energy appearing as heat in the resistor ultimately comes at the expense of the chemicalenergy of the cell.

Not always is the work done by a cell converted to heat. Immediately after a motor is connected to acell, the speed of the shaft of the motor increases. A part of the work done by the cell goes intoproducing the increase in kinetic energy. And a part is used to overcome friction, etc. When the motorachieves a constant speed, its kinetic energy does not change. So the work done by the cell is onlyused to overcome friction, etc. This appears as heat. That is why the cover over a motor becomeswarm on use.



APPLICATIONS OF THE HEATING EFFECT OF CURRENT

The heating effect of electric current has many uses. Electric bulbs, room heaters, electric irons,

immersion heaters, toasters, electric fuses and a number of other appliances work on this principle. In

all of these, a wire of suitable resistance, commonly called the heating element, is connected to the

power supply. The current passing through the element produces heat in it, which is used for some

specific purpose.

(i) Electric bulb: An electric bulb has a simple structure. It consists of a sealed glass bulb that has a

tungsten filament connected to two electrical contacts. The bulb is filled with an unreactive gas like

argon or nitrogen. To produce white light, the filament has to be heated to about 3000°C by passing a

current through it. Obviously, the material of the filament should such that it does not melt at this

temperature. Tungsten is used for the filament because its melting point is about 3400°C. The sealed

glass bulb serves two purposes. First, it protects the filament from oxidation and the effects of

humidity. Secondly, the small enclosed volume makes it easier to maintain the required temperature, as

without it the loss of heat would be more.

(ii) Fuse: A fuse is a safety device that does not allow excessive current to flow through an electric

circuit. It consists of a metallic wire of low melting point, fixed between the two terminals of a fuse

plug. The fuse plug fits into a fuse socket connected in the circuit. Fuses are available in various

shapes. The fuse plug is used in household wiring. It is made of porcelain.

A fuse is connected in series with an appliance (such as a TV) or a group of appliances (such as the

lights and fans in a room). So, the current through the fuse is the same as the current through the

appliance or the group of appliances. If this current exceeds a safe value, the heat produced in the fuse

wire causes it to melt immediately. This breaks the circuit, preventing any damage. Figure shows

examples of how a fuse is connected in circuits.

Good-quality fuse wires are made of tin, as it has a low melting point. Some fuse wires are made of an

alloy of tin and copper. The thickness of the fuse wire depends on the circuit in which it is to be used.

If a section of the circuit is meant to carry a maximum of 5A current, the fuse wire should also be able

to carry currents up to 5A. Similarly, for wiring meant for 15A, the fuse wire should be thicker, and

should be able to carry currents up to 15A.

12V 12V

(a) (b)

DISADVANTAGES OF THE HEATING EFFECT OF CURRENT

A current always produces some heat, whether we use the heat or not. If the heat produced cannot

be utilized, it represents a wastage of energy. A considerable amount of energy is thus wasted in the

transmission of electricity from the generating station to our homes. Sometimes, the heat produced in

a device is so much that it can damage the device, unless proper cooling arrangements are made. To

dissipate the heat produced in TV sets, monitors, etc., their cabinets have grills for air to pass. Certain

components of a computer get so hot that they have fans to cool them.

Page # 19


ELECTRICITY

ELECTRIC POWER

Power is the rate of doing work, or the rate at which energy is produced or consumed. The electrical

energy produced or consumed per unit time is called electric power. In an electric circuit, the power is

P =2

2U i Rti R

t t

Using iR = V

P = Vi

P = 2V

R

The energy consumed and power are related as

U = Pt.

UNIT OF POWER

The SI unit of energy is the joule, and that of time is the second. The SI unit of power is therefore

joule/second. This unit is called the watt, whose symbol is W.

RATING OF ELECTRIC APPLIANCES

Take an electric bulb and see what is written on it. Apart from the name and the symbol of the

company, we will find values of power and potential difference. For example, it could be 60W, 220V. It

means that 220V should be applied across this bulb, and when 220V is applied, the power consumedwill be 60W. We will find similar markings on all electric· appliances. For an electric appliance, the values

of power and voltage taken together form what is called the rating of the appliance.

From the rating of an appliance, you can easily calculate its resistance by using the equation P = 2V

R.

Note that higher the power rating, smaller the resistance. So, a 1000W heater has less resistance than

a 100W bulb. We can also calculate the current drawn by an appliance by using the relation i = PV .

KILOWATT HOUR

Power is the rate of energy consumed or produced. If 1 joule of energy is used per second, the energy

is used at the rate of 1 watt. In other words, if energy is used at the rate of 1 watt, the total energy

used in 1 second is 1 joule. How much energy is used in 1 hour if it is used at the rate of 1000 watt?

It is (1000 watt) × (3600 second) = 3,600,000 joule.

This amount of energy is called 1 kilowatt hour, written in short as kWh.

Thus, 1 kWh =3,600,000 J = 3.6 × 106 J.

The electrical energy used in houses, factories, etc., is measured in kilowatt hours. The cost of

electricity is fixed per kilowatt hour. One kilowatt hour of electrical energy is called one unit.



ELECTRICAL SAFETY

(A) Earthing: Earthing means to connect the metal case of electrical appliance to the earth (at zeropotential) by means of a metal wire called "earth wire". In household circuits, we have three wires, thelive wire, the neutral wire and the earth wire. One end of the earth wire is buried in the earth. Weconnect the earth wire to the metal case of the electrical appliance by using a three-pinplug.The metal casing of the appliance will now always remain at the zero potential of the earth. We saythat the appliance has been earthed or grounded. If, by chance, the live wire touches the metal caseof the electric iron (or any other appliance) which has been earthed, then the current passed directlyto the earth through the earth wire. It does not need our body to pass the current and therefore, wedo not get an electric shock. Actually, a very heavy current flows through the earth wire and the fuseof house-hold wiring blows out or melts. And it cuts off the power supply. In this way, earthing alsosaves the electrical appliance from damage due to excessive current.

(B) Miniature Circuit Breaker: These days a device called a miniature circuit breaker (MCB) is also usedinstead of or in addition of fuses, in the household electric circuits. It is a switch that automaticallyswitches off a circuit if the current in it exceeds the specified maximum limit.

COLOR CODING OF WIRES

An electric appliance is provided with a three-core flexible cable. The insulation on the three wires is ofdifferent colours. The old convention is red for live, black for neutral and green for earth. The new

international convention is brown for live, light blue for neutral and green (or yellow) for earth.

GALVANOMETER

A galvanometer is an instrument that can detect the presence of a current in a circuit. The pointerremains at zero (the centre of the scale) for zero current flowing through it. It can deflect either tothe left or to the right of the zero mark depending on the direction of current.Galvanometers are of two types:(i) Moving coil galvanometer (ii) Moving magnet galvanometer

It is used to make ammeter and voltmeter as follows:(A) Ammeter: Ammeter is an electrical instrument which measures the strength of current in 'ampere' in a

circuitry which is always connected in series in circuit so that total current (to be measured) may passthrough it. The resistance of an ideal ammeter is zero (practically it should be minimum).

(B) Voltmeter: It is an electrical instrument which measures the potential difference in 'volt' between twopoints of electric circuit. The only difference between ammeter and voltmeter is that ammeter has itsnegligible (approximately zero) resistance so that it may measure current of circuit passing through itmore accurately giving the deflection accordingly, while the voltmeter passes negligible current throughitself so that potential difference developed due to maximum current passing through circuit may bemeasured.Voltmeter has very high resistance and the resistance of an ideal voltmeter is infinite.A voltmeter is always connected in parallel.

V

Page # 21


ELECTRICITY

COLOR CODING OF RESISTORS

Digit Digit Multiplier Tolerance

4-band code

Digit Digit Multiplier Tolerance

5-band code

Digit

Color Digit Multiplier Tolerance (%)

Black 0 100(1)

Brown 1 101 1

Red 2 102 2

Orange 3 103

Yellow 4 104

Green 5 105 0.5

Blue 6 106 0.25

Violet 7 107 0.1

Grey 8 108

White 9 109

Gold 10–1 5

Silver 10–2 10

(None) 20

Note: Short trick for colors:- B B Roy of Great Britain has very good Wife.



Ex.1 A piece of wire of resistance R is cut into five equal parts. These parts are then connected inparallel. If the equivalent resistance of this combination is R', then the ratio R/R' is :(A) 1/25 (B) 1/5 (C) 5 (D) 25

Sol. Resistance of each one of the five parts = R5

Resistance of five parts connected in parallel is given by

1 1 1 1 1 1R ' R / 5 R / 5 R / 5 R / 5 R / 5 or

1 5 5 5 5 5 25R ' R R R R R R

orRR '

25

Thus, (D) is the correct answer.Ex.2 Which of the following terms does not represent electrical power in a circuit :

(A) I2R (B) IR2 (C) VI (D) V2/R

Sol. Electrical power, P = VI = (IR) I = I2R = V 2V V

R RObviously, IR2 does not represent electrical power in a circuit.Thus, (B) is the correct answer.

Ex.3 An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumedwill be:(A) 100 W (B) 75 W (C) 50 W (D) 25 W

Sol. Resistance of the electric bulbs, R = 2V

P(P = V2/R)

or R = 2(2 20 )

1 00= 484

Power consumed by the bulb when it is operated at 110 V is given by

P' = 2 2V ' (1 10 ) 1 10 1 1 0

25 WR 4 84 48 4 (V' = 100 V)

Thus, (D) is the correct answer.Ex.4 Two conducting wires of the same material and of equal lengths and equal diameters are first connected

in series and then in parallel in an electric circuit. The ratio of the heat produced in series andparallel combinations would be :(A) 1:2 (B) 2:1 (C) 1:4 (D) 4:1

Sol. Since both the wires are made of the same material and have equal lengths and equal diameters,these have the same resistance. Let it be R.When connected in series, their equivalent resistance is given by

Rs = R + R = 2RWhen connected in parallel, their equivalent resistance is given by

p

1 1 1 2R R R R or Rp =

R2

Further, electrical power is given by P = 2V

R

Power (or heat produced) in series, Ps = 2

s

VR

Power (or heat produced) in parallel, Pp = 2

p

VR

Thus,2

ps s2

p p s

RP V / R R / 2 1P V / R R 2R 4

or Ps : Pp : : 1 : 4Thus, (C) is the correct answer.

SOLVED PROBLEMS

Page # 23


ELECTRICITY

Ex.5 How is voltmeter connected in the circuit to measure potential difference between two points?

Sol. A voltmeter is always connected in parallel across the points between which the P.D. is to be determined.

Ex.6 A copper wire has a diameter of 0.5 mm and a resistivity of 1.6 × 10–6 ohm cm. How much ofthis wire would be required to make a 10 ohm coil? How much does the resistance change if thediameter is doubled?

Sol. We are given that, Diameter of the wire, D = 0.5 mm = 0.5 × 10–3 m

resistivity of copper, = 1.6 × 10–6 ohm cm = 1.6 × 10–8 ohm m

required resistance, R = 10 ohm

As R = A

, =2 2RA R( D / 4 ) RD

4 [A = r2 = (D/2)2 = D2/4]

or = –3 2

–8

3.14 1 0 (0 .5 1 0 )4 1 .6 1 0

m = 112.7 m

Since, R = 2 2

rD / 4 D , R 1/D2. When D is doubled, R becomes

14

times.

Ex.7 The values of current, I, flowing in a given resistor for the corresponding values of potential difference,V, across the resistor are given below :

I (ampere) : 0.5 1.0 2.0 3.0 4.0

V (volt) : 1.6 3.4 6.7 10.2 13.2

Plot a graph between V and I and calculate the resistance of the resistor.

Sol. The V-I graph is as shown in fig.

I (ampere)

4.0

3.0

2.0

1.0

1.40

2.65

0.5

1.25A

4V

(0,0) 1 2 51.6 3.4 6 6.7 7 8 9 10 11 12 1310.2 13.2 14V(volt)

For V = 4V (i.e., 9V – 5V), I = 1.25 A (i.e., 2.65 A – 1.40 A). Therefore, R = V 4 VI 1.2 5 A

= 3.2

The value of R obtained from the graph depends upon the accuracy with which the graph is plotted.

Ex.8 When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA inthe circuit. Find the value of the resistance of the resistor.

Sol. Here, V = 12 V, I = 2.5 mA = 2.5 × 10–3 A

Resistance of the resistor, R = VI

= –3

1 2 V2 .5 1 0 A

= 4800 = 4.8 k

Ex.9 A battery of 9 V is connected in series with resistors of 0.2 , 0.3 , 0.4 , 0.5 and 12 . How muchcurrent would flow through the 12 resistor?

Sol. Since all the resistors are in seies, equivalent resistance,

Rs = 0.2 + 0.3 + 0.4 + 0.5 + 12 = 13.4

Current through the circuit, I = s

V 9 V0 .67 A

R 1 3.4

In series, same current (I) flows through all the resistors. Thus, current flowing through 12 resistor= 0.67 A



Ex.10 How many 176 resistors (in parallel) are required to carry 5 A in 220 V line?Sol. Here, I = 5A, V = 220 V.

Resistance required in the circuit, R = V 2 20 V

4 4I 5 A

, Resistance of each resistor, r = 176

If n resistors, each of resistance r, are connected in parallel to get the required resistance R, then

R = rn

or 44 = 17 6

nor n =

17 64 4

= 4

Ex.11 Show how you would connect three resistors, each of resistance 6 , so that the combination hasa resistance of (i) 9 (ii) 2 .

Sol. (i) In order to get a resistance of 9 from three resistors, each of resistance 6 , we connect tworesistors in parallel and this parallel combination (or resistance 3 ) in series with the third resistor asshown in fig.

D

6

6

CA B A C D B

(a)

A B6 6 9

(ii) In order to get a resistance of 2 from three resistors, each of resistance 6 , we connectall the three resistors in parallel as shown in fig (b) as equivalent resistance in parallel combination,

i.e., Rp is given by Rp = 63 = 2 .

6

6

6

A B

(b)

A B

Ex.12 Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. Howmany lamps can be connected in parallel with each other across the two wires of 220 V line ifthe maximum allowable current is 5 A?

Sol. Resistance of each bulb, r = 2 2V (2 20 )

4 84 0P 1 0

Total resistance in the circuit, R 22 0 V

445 A

Let n be the number of bulb (each of resistance r) to be connected in parallel to obtain a resistance R.

Clearly, R = rn

or n = r 48 40

1 10R 44

Ex.13 A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, eachof 24 resistance, which may be used separately, in series, or in parallel. What are the currentsin the three cases?

Sol. Here, potential difference, V = 220 VResistance of each coil, r = 24 (i) When each of the coils A or B is connected separately, current through each foil, i.e.,

I = V 2 2 0 V 9 .2 Ar 2 4

(ii) When coils A and B are connected in series, equivalent resistance in the circuit,Rs = r + r = 2r = 48

Current through the series combination, ie.e, Is = s

V 2 2 0 V 4.6 AR 48

(iii) When the coils A and B are connected in parallel, equivalent resistance in the circuit,

Rp = r 24 1 22 2

Current through the parallel combination, ie.e, Ip = p

V 2 20 V 1 8.3 AR 1 2

Page # 25


ELECTRICITY

Ex.14 Compare the power used in the 2 resistor in each of the following circuits :

(i) a 6 V battery in series with 1 and 2 resistors, and

(ii) a 4 V battery in parallel with 12 and 2 resistors.

Sol. (i) Since 6 V battery is in series with 1 and 2 resistors, current in the circuit,

I = 6 V 6 V

2 A1 2 3

Power used in 2 resistor, P1 = I2R = (2A)2 × 2 = 8W

(ii) Since 4 V battery is in parallel with 12 and 2 resistors, pd across 2 resistor, V = 4V.

Power used in 2 resistor, P2 = 2 2V (4 V) 8 W

R (2 )

Clearly, 1

2

P 8 W1

P 8 W

Ex.15 Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallelto the electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Sol. Resistance of first lamp, r1 = 2 2V (2 20 )

4 84P 1 0 0

resistance of the second lamp, r2 = 2 2V (2 20 )

80 6 .7P 6 0

Since the two lamps are connected in parallel, the equivalent resistance is given by

2 1

p 1 2 1 2

1 1 1 r rR r r r r

or Rp = 2 1

1 2

r r 4 84 8 0 6.7 39 04 4 2.8r r 4 84 8 06.7 12 90 .7 = 302.5

Current drawn from the line, i.e., I = p

V 2 20 VR 30 2 .6 = 0.73 A

Ex.16 Which uses more energy, a 250 W TV set in 1 h, or a 1200 W toaster in 10 minutes?

Sol. Energy used by 250 W TV set in 1 h = 250 W × 1h = 250 Wh

Energy used by 1200 W toaster in 10 min. (i.e., 1/6 h) = 1200 W × (1/6) h = 200 WhThus, a 250 W TV set uses more power in 1 h than a 1200 W toaster in 10 minutes.

Ex.17 An electric heater of resistance 8 draws 15 A from the service mains for 2 hour. Calculate therate at which heat is developed in the heater.

Sol. Here, I = 15A, R = 8 , t = 2h

Rate at which heat is developed, i.e, electric power, P = I2 R = (15)2 × 8 = 1800 W = 1800 J/s

Ex.18 Explain the following :

(a) Why is tungsten used almost exclusively for filament of incandescent lamps?

(b) Why are the conductors of electric heating devices, such as toasters and electric irons, madeof an alloy rather than a pure metal?

(c) Why is the series arrangement not used for domestic circuits?

(d) How does the resistance of a wire vary with its cross-sectional area?

(e) Why are copper and aluminium wires usually employed for electricity transmission.Sol. (a) Tungsten has a high melting point (3380°C) and becomes incandescent (i.e., emits light at a

high temperature) at 2400 K.

(b) The resistivity of an alloy is generally higher than that of pure metals of which it is made of.(c) In series arrangement, if any one of the appliances fails or is switched off, all the other appliancesstop working because the same current is passing through all the appliances.

(d) The resistance of a wire (R) varies inversely as its cross-sectional area (A) as R 1/A.

(e) Copper and Aluminium wires possess low resistivity and as such are generally used for electricitytransmission.



Q.1 What does an electric circuit mean ?Ans. An electric circuit is a closed and continuous path consisting of many devices like resistors, electric

bulbs, etc. through which an electric current flows.

Q.2 Define the unit of current.Ans. The 51 unit of current is ampere (A). Current flowing through a conductor Is said to be 1 ampere if 1

coulomb of charge flows through it in 1 second.

Q.3 Calculate the number of electrons constituting one coulomb of charge.Ans. Number of electrons constituting 1 coulomb is given by,

n = Qe

, where, Q = 1 C and e = charge of a single electron = 1.6 × 10–19 C

or n = 19

1C

1.6 10 C = 6.25 × 1018 electrons.

Q.4 Name a device that helps to maintain a potential difference across a conductor.Ans. A battery can be used to maintain a potential difference across a conductor.

Q.5 What is meant by saying that the potential difference between two points is 1 V ?Ans. Potential difference between two points is 1 volt if 1 joule of work is done to carry a charge of 1

coulomb from one point to the other.

Q.6 How much energy is given to each coulomb of charge passing through a 6V battery?Ans. Work done, W = QV Where, Q = 1C; V = 6V W = 1C × 6V = 6J

Q.7 On what factors does the resistance of a conductor depend?Ans. The resistance (R) of a conductor depends upon

(i) its length ( ): R

(ii) its cross-sectional area (A): R 1A

(iii) Nature of material i.e., resistivity ( ) of its material: R (iv) Temperature: more the temperature, more will be its resistance.

Q.8 Does current flow more easily through a thick wire or a thin wire of the same material when connectedto the same source? Why?

Ans. The current flows more easily through a thick wire than through a thin wire. This is because theresistance R of a thick wire (large area of cross-section) is less than that of a thin wire (small area of

cross-section) as R 1A

.

Q.9 Let the resistance of an electrical component remains constant while the potential difference acrossthe two ends of the component decreases to half its former value. What change will occur in thecurrent through it?

Ans. We know that I = V/R, when potential difference becomes V/2, and resistance remains constant, then,current becomes 1/2 of its former value.

NCERT QUESTIONS WITH SOLUTIONS

Page # 27


ELECTRICITY

Q.10 Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

Ans. This is because (i) resistivity of an alloy is generally higher than that of pure metals (ii) an alloy has ahigh melting point and it does not oxidise at high temperatures.

Q.11 (a) which among iron and mercury is a better conductor? Given, iron = 10.0 × 10–8 m and mercury =94.0 × 10–8 m.

(b) Which material is the best conductor?

Ans. (a) Iron is a better conductor than mercury as resistivity ( ) for iron is less than that for mercury.(b) Silver is the best conductor because its resistivity ( ) is least.

Q.12 Draw a schematic diagram of a circuit consisting of a battery of three cells of 2V each, a 5 ohmresistor, an 8 ohm resistor, and a 12 ohm resistor, and a plug key, all connected in series.

Ans.

(2V2V 2V kk

I

Q.13 Redraw the circuit of Q. 12, putting in an ammeter to measure,the current through the resistors and avoltmeter to measure the voltage across the 12 ohm resistor. What would be the reading in theammeter and the voltmeter?

(2V2V 2V kk

I

(2V2V 2V kk

I

V

A+

+

Ans. Since all the three resistances are in series, total resistance in the circuit,

R = 5 + 8 + 12 = 25

Current in the circuit, V 2 2 2 6

I 0.24 AR 25 25

, thus, ammeter will read 0.24 A.

Potential difference across 12 ohm resistor, V = I × R = 0.24 × 12 = 2.88 V

Q.14 Judge the equivalent resistance when the following are connected in parallel (a) 1 and 106 (b) 1 ,103 and 106 .

Ans. (a) Approx. 1 (slightly less than 1 ) as other one (106 ) is very large as compared to 1 . In parallelcombination of resistors, the equivalent resistance is lesser than the least resistance (in this case, 1 ).

(b) Again, resistance is approx. 1 (slightly less than 1 ).

Q.15 An electric lamp of 100 , a toaster of resistance 50 and a water filter of resistance 500 areconnected in parallel to a 220V source. What is the resistance of an electric iron connected to thesame source that takes as much current as in three appliances and what is current through it?

Ans. Resistance of the electric lamp, R1 = 100 ; resistance of toaster, R2 = 50 ; resistance of water filter,R3 = 500

Since R1, R2 and R3 are connected in Parallel, their equivalent resistance (Rp) is given by

p 1 2 3

1 1 1 1 1 1 1 5 10 1 16 4R R R R 100 50 500 500 500 125 p

125R

4



Current through the three appliances, i.e.,

p

V 220I 7.04 A

R 125 /4

Since the electric iron drawing the same current when connected to the same source (220 V), itsresistance must be equal to Rp.

Thus, resistance of the electric iron, 125

31.254

Current through the electric iron, I = 7.04 A

Q.16 What are the advantages of connecting electrical devices in parallel with the battery instead ofconnecting them in series.

Ans. (a) In case of devices in parallel. if one device gets damaged (or open), all other will work as usual asthe whole circuit does not break. This is not with the devices connected in series because when onedevice fails, the circuit breaks and all devices stop working.

(b) Since potential difference across all devices is same in parallel Circuit, they will draw requiredcurrent according to their resistances. This is not so in series circuit where same current flows throughall the devices, irrespective of their resistances.

Q.17 How can three resistors of resistances 2 , 3 and 6 be connected to give a total resistance of (a) 4(b) 1 ?

Ans. (a) The get a total resistance of 4 from resistors of resistance 2 , 3 and 6 , the resistors are joinedas shown below.

A B

The resistors having resistances 3 and 6 are connected in parallel. This combination is connected inseries with the resistor of resistance 2 . Let us check it mathematically, equivalent resistance of 3and 6 resistors is,

13 6 3 6

R 23 6 9

Now, R1 and 2 resistors are in series, their equivalent resistance is Re = R1 + 2 = 2 + 2 = 4 .

(b) To get a resistance of 1 from three given resistors of resistance 2 , 3 , 6 , are joined as shownbelow.

A B

They all are connected in parallel. Their equivalent resistance is given by,

1 1 1 1 3 2 1 61

R 2 3 6 6 6 R =

Page # 29


ELECTRICITY

Q.18 What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four

coils of resistance 4 , 8 , 12 , 24 ?

Ans. (a) The highest resistance is secured when all the resistors are connected in series. The equivalent

resistance is given by,

Re = 4 + 8 + 12 + 24 = 48 .

(b) The lowest resistance is secured when all the four coils are connected in parallel. The equivalent

resistance is given by,

e

1 1 1 1 1 6 3 2 1 12 1R 4 8 12 24 24 24 2 or Re = 2

Q.19 Why does the cord of electric heater not glow while the heating element does?

Ans. The cord of an electric heater is made of thick copper wire and has much lower resistance than the

heating element. For the same current (I) flowing through the cord and the element, heat produced in

the element is much more than that produced in the cord. As a result, the element becomes very hot

and glows whereas the cord does not become hot and as such does not glow.

Q.20 Compute the heat generated while transferring 96000 coulombs of charge in one hour through a

potential difference of 50 V.

Ans. Here, charge, Q = 96000C; time, t = 1 hr

potential difference, V = 50V.

Heat produced, H = V I t = V × q [ q = I t]

= 96000C × 50V = 4.8 × 106 J.

Q.21 An electric iron of resistance 20 takes a current of 5A. Calculate the heat developed in 30s.

Ans. Here, resistance, R = 20 , current, I = 5A, time, t = 30 s.

Heat produced, H = I2 R t = (5)2 5 20 × 30 = 1.5 × 104 J.

Q.22 What determines the rate at which energy is delivered by a current?

Ans. Electric power determines the rate at which energy is delivered by a current.

Q.23 An electric motor takes 5A from a 220V. Determine the power and energy consumed in 2Hr.

Ans. Here, current, I = 5A; potential difference, V = 220V; time, t = 2hr = 2 × 60 × 60 = 72000

= 7.92 × 106 J



Q.1 Define resistivity of a material. [2004]

Q.2 A cylinder of a material is 10 cm long and has

a cross-section of 2 cm2. If its resistance along

the length be 20 , what will be its resistivity

in number and units. [2004]

Q.3 Why is tungsten metal selected for making

filaments of incandescent lamps ? [2005]

Q.4 A resistance of 10 ohm is bent in the form of a

closed circle. What is the effective resistance

between the two points at the ends of any

diameter of this circle? [2005]

Q.5 A wire of resistance 5 is bent in the form of a

closed circle. What is the resistance between

two points at the ends of any diameter of the

circle ? [2005]

Q.6 A wire of resistance 20 is bent in the form of

a closed circle. What is the effective resistance

between the two points at the ends of any

diameter of the circle? [2005]

Q.7 Why is much less heat generated in long electric

cables than in filaments of electric bulbs?

[2005]

Q.8 State which has a higher resistance: a 50 W

or a 25 W lamp bulb and how many times?

[2005]

Q.9 What is the power of torch bulb rated at 2·5 V

and 500 mA ? [2005]

Q.10 There are two electric bulbs, (i) marked 60 W,

220 V and (ii) marked 100 W ; 220 V. Which

one of them has higher resistance ? [2006]

Q.11 Out of the two, a toaster of 1 kW and an

electric heater of 2 kW, which has a greater

resistance? [2006]

Q.12 What is the SI unit of electrical potential ?

[2007]

Q.13 What is meant by the statement "Potential

difference between two points A and B in an

electric circuit is 1 volt ? [2007]

Q.14 Why is series arrangement not used for

connecting domestic electrical appliances in a

circuit ? [2008]

Q.15 Out of 60 W and 40 W lamps, which one has a

higher resistance when in use? [2008]

Q.16 An electric bulb draws a current of 0·2 A when

the voltage is 220 volts. Calculate the amount

of charge flowing through it in one hour.

[2004]

Q.17 An electric iron draws a current of 0·5 A when

the voltage is 200 volts. Calculate the amount

of electric charge flowing through it in one

hour. [2004]

Q.18 An electric appliance draws a current of 0·4 A

when the voltage is 200 volts. Calculate the

amount of charge flowing through it in one

hour. [2004]

Q.19 Calculate the amount of charge that would

flow in 1 hour through the element of an electric

bulb drawing a current of 0·2 A. [2004]


flow in 2 hours through the element of an

electric bulb drawing a current of 0·25 A.

[2004]


flow in 1 hour through the element of an electric

iron drawing a current of 0·4 A. [2004]

Q.22 Derive the relation R = R1 + R2 + R3 when

resistors are joined in series. [2005]

Q.23 (i) Draw a circuit diagram to show how two

resistors are connected in series. [2006]

(ii) In a circuit if the two resistors of 5 and

10 are connected in series, how does the

current passing through the two resistors

compare ?

Q.24 A bulb is rated at 5.0 V, 100 mA. Calculate its

(i) power and (ii) resistance. [2006]

BOARD PROBLEMSEXERCISE – I

Page # 31


ELECTRICITY

Q.25 An electric iron has a rating of 750 W, 220 V.

Calculate [2007]

(i) current passing through it, and

(ii) its resistance, when in use.

Q.26 An electric lamp is marked 100 W, 220 V. It is

used for 5 hours daily. Calculate [2007]

(i) its resistance while glowing

(ii) energy consumed in kWh per day.

Q.27 Three resistors are connected as shown in Fig.

Through a resistor of 5 ohm, a current of 1

ampere is flowing. [2003]

R = 102

R = 51I1 I1 I1

I2

R = 152I3A B C

(a) What is the potential difference across AB

and across AC ?

(b) What is the current through the other two

resistors ?

(c) What is the total resistance?

Q.28 An electric bulb is rated at 200 V-100 W. What

is its resistance? Five such bulbs burn for 4

hours. What is electrical energy consumed ?

Calculate the cost if the rate is 50 paise unit.

[2003]

Q.29 State the formula co-relating the electric

current flowing in a conductor and the voltage

applied across it. Also show this relationship

by drawing a graph.

What would be the resistance of a conductor

if the current flowing through it is 0·35 ampere

when the potential difference across it is 1·4

volt. [2004]

Q.30 When a potential difference of 1·2 volt is applied

across a conductor, the current flowing through

it is 0·25 ampere. Calculate the resistance of

the conductor. [2004]

Q.31 (i) State the formula showing how the current

I in a conductor varies when the potential

difference V applied across it is increased

stepwise [2004]

(ii) Show this relationship also on a schematic

graph.

(iii) Calculate the resistance of a conductor if

the current flowing through it is 0·2 ampere

when the applied potential difference is 0·8

volt.

Q.32 A torch bulb is rated 5·0 V and 500 mA.

Calculate its (i) power (ii) resistance and (iii)

energy consumed when it is lighted for 4 hours.

[2005]

Q.33 If a 12 V battery is connec ted to the

arrangement of resistances given in Fig. (with

5 replaced by 10 , 15 replaced by 5

and 10 replaced by 25 ). Calculate (i) the

total effective resistance of the arrangement

and (ii) the total current flowing in the circuit.

[2005]

I

24V

I

5 20

15

( )

10

Q.34 Two electric lamps of 100 W and 25 W

respectively are joined in parallel to a supply

of 200 V. Calculate the total current flowing

through the circuit. [2005]

Q.35 Two identical resistors, each of resistance 2

, are connected in turn (i) in series, and (ii)

in parallel, to a battery of 12 V. Calculate the

ratio of power consumed in the two cases.

[2005]

Q.36 Two identical resistors, each of resistance 10

are connected in (i) series, and (ii) in parallel,

in turn to a battery of 10 V. Calculate the ratio

of power consumed in the combination of

resistors in the two cases. [2005]



Q.37 In the given circuit, ca lculate (i) tota l

resistance of the circuit, and (ii) current shown

by the ammeter. [2005]

P Q

R = 53

R =31 R =22

A2.5V

+ –

Q.38 (i) Draw a schematic diagram of a circuit

consisting of a battery of five 2 V cells, a 5

resistor, a 10 resistor and a 15 resistor,

and a plug key, all connected in series. [2006]

(ii) Calculate the current passing through the

above circuit when key is closed.

Q.39 In a household, 5 tube lights of 40 W each are

used for 5 hours and an electric press of 500

W for 4 hour each day. Calculate the total

energy consumed by the tube lights and press

in a month of 30 days. [2006]

Q.40 In the circuit shown in Fig., calculate : (a)

total resistance in arm CE, (b) total current

drawn from the battery, and (c) current in each

arm, i.e., AB and CE of the circuit. [2006]

3V

+ –

A B

2 4

6

( )

DC E

I1

I2

Q.41 (a) What is meant by 'Electric Resistance' of a

conductor? [2007]

(b) A wire of length L and resistance R is

stretched so that its length is doubled and

area of cross· section is halved. How will its :

(i) resistance change ?

(ii) resistivity change ?

Q.42 (a) State Ohm's law. [2007]

(b) Draw a schematic diagram of the circuit

for studying Ohm's law.

Q.43 Two lamps, one rated 60 W at 220 V and the

other 40 W at 220 V, are connected in parallel

to the electric supply at 220 V. [2008]

(a) Draw a circuit diagram to show the

connections.

(b) Calculate the current drawn from the

electric supply.

(c) Calculate the total energy consumed by

the two lamps together when they operate for

one hour.

Q.44 (a) Distinguish between the terms 'overloading'

and 'short-circuiting' as used in domestic

circuits. [2008]

(b) Why are the coils of electric toasters made

of an alloy than a pure metal ?

Q.45 For the circuit shown in Fig., calculate

(a) the value of cu rrent through each

resistance [2008]

(b) the total current in the circuit

(c) the total effective resistance of the circuit.

5

10

30

I1I2

I3I I

6V

+–( ) A

Q.46 (a) Express Ohm's law by a mathematical

formula. [2004]

(b) Draw a circuit diagram to verify Ohm's law.

(c) Present the relationship between the

voltage applied across a conductor and the

current flowing through it graphically.

Page # 33


ELECTRICITY

Q.47 State Ohm's law. Express it mathematically.

Define SI unit of resistance. Derive an

expression for the equivalent resistance of three

resistors R1, R2 and R3 connected in series (or

in parallel). [2004]

Q.48 (a) Express Ohm's law both by a mathematical

formula and by a graph line. [2004]

(b) State SI units of

(i) resistance and

(ii) resistivity.

(c) What will be the equivalent resistance of

two resistors R1 and R2

(i) connected in series and

(ii) connected in parallel.

Q.49 (a) What is meant by saying that the potential

difference between two points is 1 volt? Name

a device that helps to measure the potential

difference across a conductor. [2008]

(b) Why does the connecting cord of an electric

heater not glow hot while the heating element

does ?

(c) Electrical resistivities of some substances

at 20°C are given below:

Silver 1·60 × 10–8 m

Copper 1·62 × 10–8 m

Tungsten 5·20 × 10–8 m

Iron 10·0 × 10–8 m

Mercury 94·0 × 10–8 m

Nichrome 100 × 10–6 m

Answer the following questions in relation to

them :

(i) Among silver and copper, which one is a

better conductor? Why ?

(ii) Which material would you advise to be used

in electrical heating devices ? Why ?

Q.50 (a) Name an instrument that measures electric

current in a circuit. Define the unit of electric

current. [2008]

(b) What do the following symbols mean in

circuit diagram ?

0.50.81.01.21.51.6

0 0.1 0.2 0.3 0.4 0.5 0.6

V (volt)

I(A)

(i) (ii) ( )

(c) An electric circuit consisting of a 0·5 m

long nichrome wire XY, an ammeter, a voltmeter,

four cells of 1·5 V each and a plug key was set

up.

(i) Draw a diagram of this electric circuit to

study the relation between the potential

difference maintained between the points 'X'

and 'Y' and the electric current flowing through

XY.

(ii) Graph shown in Fig. was plotted between

V and I values.

What would be the values of V/I ratios when

the potential difference is 0·8 V, 1·2 V and 1·6

V respectively? What conclusion do you draw

from these values ?



Q.1 If a charged body attracts another body,the charge on the other body :-

(A) must be negative(B) must be positive

(C) must be zero(D) may be negative or positive or zero

Q.2 1 MeV is equal to :-

(A) 1.6 × 10–19 J (B) 1.6 × 10–14 J(C) 1.6 × 10–13 J (D) 1.6 × 10+13 J

Q.3 A man has five resistors each of value 15 .

What is the maximum resistance he canobtain by connecting them ?

(A) 1 (B) 5

(C) 12

(D) 25

Q.4 Materials which allow larger currents to flowthrough them are called :-

(A) Insulators (B) Conductors(C) Semiconductors(D) Alloys

Q.5 If I is the current through a wire and e isthe charge of electrons, then the numberof electrons in t seconds will be givenby :-

(A) Iet

(B) Ite

(C) e/It (D) It/e

Q.6 Conventionally, the direction of the currentis taken as -

(A) the direction of flow to negative charge(B) the direction of flow of atoms

(C) the direction of flow of molecules(D) the direction of flow of positive charge

Q.7 The unit of specific resistance is :-

(A) ohm (B) mho(C) ohm-metre (d) ohm per metre

Q.8 1 volt equals :-

(A) 1 joule(B) 1 joule per coulomb

(C) 1 coulomb per metre(D) 1 newton per coulomb

Q.9 The reciprocal of resistance is conductance.If the unit of resistance is ohm, the unitof conductance will be -

(A) ohm (B) volt(C) mho (D) ohm metre–1

Q.10 Good conductors have many loosely bound-

(A) atoms (B) molecules(C) protons (D) electrons

Q.11 One ampere equals :-

(A) 106 A (B) 10–6 A(C) 10–3 A (D) 10 A

Q.12 How many electrons constitute a current ofone microampere?

(A) 6.25 × 106 (B) 6.25 × 1012

(C) 6.25 x 109 (D) 6.25 × 1015

Q.13 The SI unit of specific resistance is :-

(A) ohm m (B) ohm m–1

(C) ohm m2 (D) (ohm)–1

Q.14 The effective resistance of a c ircu itcontaining resistances in parallel is -

(A) equal to the sum of the individualresistances

(B) smaller than any of the individualresistances

(C) greater than any of the individualresistances

(D) sometimes greater and sometimes smallerthan the individual resistances

Q.15 Electric field intensity is

(A) a scalar quantity(B) a vector quantity

(C) neither scalar nor vector(D) sometimes scalar and sometimes vector

Q.16 Electric potential is

(A) A scalar quantity(B) a vector quantity

(C) neither scalar nor vector(D) sometimes scalar and sometimes vector

Q.17 In Coulomb's law, t he constant ofproportionality k has the units -

(A) N (B) Nm2

(C) NC2/m2 (D) Nm2/C2

Q.18 The variable resistance is called :-

(A) resistor (B) rheostat(C) open switch (D) none of these

Q.19 The law that governs the force betweenelectric charges is called -

(A) Ampere's law (B) Coulomb's law(C) Faraday's law (D) Ohm's law

OLYMPIAD QUESTIONSEXERCISE – II

Page # 35


ELECTRICITY

Q.20 A charge q is placed at the center of theline joining two equal charges Q. The systemof the three charges will be in equilibrium,if q is equal to -

(A) Q2

(B) –Q4

(C) +Q4

(D) +Q2

Q.21 The force between two electrons separatedby a distance r varies as :-

(A) r2 (B) r(C) r–1 (D) r–2

Q.22 When the distance between the chargedparticles is halved, the force between thembecomes -

(A) One-fourth (B) Half(C) Double (D) Four times

Q.23 A charge q1 exerts some force on a secondcharge q2. If third charge q3 is brought near,the force of q1 exerted on, q2 :-

(A) Decreases

(B) Increases

(C) Remains unchanged

(D) Increases if q3 is of the same sign asq1 and decreases if q3 is of opposite sign

Q.24 If the charge is moved against the coulombforce of an electric field -

(A) Work is done by the electric field(B) Energy is used from some outside force

(C) The strength of the field is decreased(D) The energy of the system is decreased

Q.25 The ratio of the forces between two smallspheres with constant charge (a) in air (b)in a medium of dielectric constant K is-

(A) 1 : K (B) K : 1(C) 1 : K2 (D) K2 : 1

Q.26 Two charges are placed at a distance. If aglass slab is placed between them, forcebetween them will be

(A) Zero (8) Increased(C) Decreased (D) Remains same

Q.27 If a unit positive charge is taken from onepoint to another over an equipotentia lsurface, then -

(A) Work is done on the charge(B) Work is done by the charge

(C) Work done is constant(D) No work is done

Q.28 If a glass rod is rubbed with silk, it acquiresa positive charge because-

(A) Protons are added to it(C) Electrons are added to it

(B) Protons are removed from it(D) Electrons are removed from it

Q.29 Two resistors of resistance R1 and R2 havingR1 > R2 are connected in parallel. Forequivalent resistance R, the correctstatement is -

(A) R > R1 + R2(B) R1 < R < R2

(C) R2 < R < (R1 + R2)(D) R < R1

Q.30 Two unequal resistances are connected inparallel. Which one of the statement iscorrect-

(A) The current flowing is same in both

(B) More current wi ll f low from higherresistance piece

(C) The potential drop is same in both

(D) The conductivity of lower resistance isless

Q.31 There are 8 equal resistances R. Two areconnected in parallel, such four groups areconnected in series, the total resistance

(A) R/2 (B) 2R(C) 4R (D) 8R

Q.32 In a conductor 4 coulombs of charge flowsfor 2 seconds. The value of electric currentwill be-

(A) 4V (B) 4A(C) 2A (D) 2V

Q.33 In a conductor, the flow of current is :-

(A) Flow of molecules(B) Flow of free electrons

(C) Flow of positive charge(D) Flow of ions

Q.34 Three resistances of magnitude 2, 3 and 5ohm are connected in parallel to a batteryof 10 volts and of negligible resistance. Thepotential difference across 3 resistance willbe-

(A) 2V (B) 3V(C) 5V (D) 10V



Q.35 In the circuit shown below, the ammeter Areads 5A and the voltmeter V reads 20 V(Fig.). The correct value of resistance R is:-

V

RA

(A) exactly 4(B) slightly greater than 4(C) slightly less than 4(D) zero

Q.36 What is the current in the circuit shown (Fig.)

2 2

2

2V

I

(A) 1.5 A (B) 0.5 A(C) 2.5 A (D) none of these

Q.37 In the circuit shown in Fig., the reading ofthe voltmeter V will be :-

– +2100

V

12V

(A) 4V (B) 2V(C) 6V (D) 3V

Q.38 Which of the following networks yields maximumeffective resistance between A and B?

(A) A B

2

2

2

(B)

2 2

2A B

(C)

2

2 2BA

(D) BA

2

2

2

Q.39 What is the resistance between A and B inthe given network (Fig.) ?

1 1

2

2

A B

(A) 2 (B) 2

(C) 32

(D) 23

Q.40 The equivalent resistance between A and B(Fig.) will be :-

22 2

1A

B(A) 7 (B) 2

(C) 53 (D) 1

Q.41 What is the resistance between A and B ?

2 2

22 2

A B

(A) 34

(B) 43

(C) 163 (D) infinity

Q.42 The slope of voltage (V) versus current (I)is called :-

V

IX

Y

O

(A) resistance (B) conductance(C) resistivity (D) conductivity

Q.43 The current in the adjoining circuit will be-

302V

i

30

30

(A) 1

45 A (B) 1

15 A

(C) 1

10 A (D) 15 A

Page # 37


ELECTRICITY

Q.44 The resistance wires are made of the material

having :-

(A) Low speci fic resistance and low

temperature coefficient of resistance.

(B) High speci fic resistance and low


(C) Low spec i fic resistance and high


(D) H igh speci fic resistance and high


Q.45 The resistance between points A and B in

Fig. is :-

R

R

R

R

R

(A) 73 R (B) 3R

(C) 5R (D) 43 R

Q.46 Two wires of same material and same mass

have their lengths in the ratio 1 : 2. Their

electrical resistances are in the ratio

(A) 1 : 1 (B) 1: 2

(C) 2: 1 (D) 1: 4

Q.47 A 24 V potential difference is applied across

a parallel combination of four 6-ohm resistors.

The current in each resistor is

(A) 1A (B) 4A

(C) 16 A (D) 36 A

Q.48 Three resistors in parallel have an effective

res is tance of 1 ohm. When they are

connected in series their resistance is 9 ohm.

The resistance of each resistor is :

A 4, 4, 1 ohm (B) 6, 2, 1 ohm

(C) 3, 3, 3 ohm (D) 2, 3, 4 ohm

Q.49 Four 20 ohm res ist ors are connected

together to form a square. The resistance

between opposite corners will be :-

(A) 20 ohm (B) 22 ohm(C) 24 ohm (D) 24.8 ohm

Q.50 The cost of electricity is about 30 paise per

unit for household use. This unit is the same

as

(A) ohm (B) ampere

(C) volt (D) kilowatt-hour

Q.51 A fuse wire should have

(A) low resistance and low melting point

(B) low resistance and high melting point.

(C) high resistance and low melting point.

(D) high resistance and high melting point.

Q.52 A one-ohm and half-ohm res istor are

connected in parallel across a 3 volt battery.

Total energy given out per second is

(A) 27 J (B) 9 J(C) 4.5 J (D) 3 J

Q.53 Two electric lamps each of 100 watts 220

V are connected in series to a supply of 220volts. The power consumed would be

(A) 100 watts (B) 200 watts

(C) 25 watts (D) 50 watts

Q.54 A rheostat can be used in an electrical circuit

as a

(A) standard resistance(B) potential divider

(C) heat controller

(D) on-off switch

Q.55 The potential difference between points A

and B of adjoining figure is

A B

CD

2V

5 5

55

55

(A) 23

V (B) 89

V

(C) 43 V (D) 2 V



Q.56 the value of equivalent resistance betweenthe points A and B in the given circuit, willbe [NTSE]

A

BR

R R

R R

R

(A) 6 R (B) 4R11

(C) 11R

4(D)

R6

Q.57 Consider a simple circuit containing a batteryand three identical incandescent bulbs A, Band C. Bulb A is wired in parallel with bulbB and this combination is wired in series withbulb C. What would happen to the brightnessof the other two bulbs if bulb A were to

burn out? [NTSE]

A

B

C

VI

(A) Only bulb B would get brighter

(B) Both A and B would get brighter

(C) Bulb B would get brighter and bulb Cwould get dimmer

(D) There would be no change in thebrightness of either bulb B or bulb C.

Q.58 Three equal resistors connected in seriesacross a source of emf dissipates 10 wattsof power. What will be the power dissipatedis watts if the same resistors are connectedin parallel across the same source of emf?

(A) 10W (B) 30W [NTSE]

(C) 90W (D) 10

W3

Q.59 Eight identical spherical mercury dropscharged to a potential of 20V each arecoalesced into a single spherical drop

[NTSE]

(A) the internal energy of the system remainsthe same

(B) the new potential of the drop is 80V

(C) internal energy of the system decreases

(D) the potential remains the same i.e. 20V

Q.60 A technician has 10 resistors each of

resistance 0.1 . The largest and smallestresistance that he can obtain by combining

these resistors are [NTSE]

(A) 10 and 1 respectively

(B) 1 and 0.1 respectively

(C) 1 and 0.01 respectively

(D) 0.1 and 0.01 respectively

1. D 2. C 3. A 4. B

5. D 6. D 7. C 8. B

9. C 10. D 11. A 12. B

13. A 14. B 15. B 16. A

17. D 18. B 19. B 20. B

21. D 22. D 23. C 24. B

25. B 26. D 27. D 28. D

29. D 30. C 31. B 32. C

33. B 34. D 35. B 36. A

37. A 38. A 39. D 40. D

41. C 42. A 43. C 44. B

45. A 46. D 47. B 48. C

49. A 50. D 51. A 52. A

53. D 54. B 55. C 56. C

57. C 58. C 59. B 60. C

ANSWER KEY

Page # 39CHEMICAL REACTIONS AND EQUATIONS


INTRODUCTIONWe observe many chemical changes taking place in our daily life. The milk turns sour if kept for a longtime at room temperature, milk changes to curd, rusting of iron, digestion of food in our body areexamples of chemical changes.

In such changes, the nature and the properties of the substances change and we say a chemicalreaction has taken place.

A chemical reaction is represented by a chemical equation which is a convenient way of describing achemical reaction with the help of symbols of elements and formulae of chemical compounds.

In this chapter, we shall discuss about chemical formulae, chemical equations, balancing of chemicalequations and types of chemical reactions.

Physical change :– A change in which the physical properties of the substance changes but thechemical composition does not change. The substance is restored to its original state as soon as thecause of change is withdrawn.

Chemical change :– In a chemical change, at least one of the reacting substance changes into a newsubstances with a different composition. The new substances can not be changed back to the originalsubstance even if the cause of change is withdrawn.

DIFFERENCE BETWEEN PHYSICAL & CHEMICAL CHANGES.No. Physical change Chemical change

1 The identity of the substance is maintained.

The identity of the original substance is completely lost.

2 The change is temporary, the substance returns to its original state as the cause of. change is withdrawn

The change is permanent.

3 No new substance is produced. A new substance is always produced.

4 Heat change may or may not occur.

Heat change may occur.

5 Only the physical state or some of the physical properties of the substances are changed

The substance after the change can not come back to its original state even when the cause of change is withdrawn.

6 Eg. Iron tawa is left exposed to air, melting of wax.

Eg. Fermentation of rice, breathing, curding of milk.

CHEMICAL REACTIONThe processes, in which a substance or substances undergo a chemical change to produce new substanceor substances, with entire new properties, are known as chemical reaction.

The nature and identity of products totally changes from the reactants.

Some important characteristics of chemical reactions are:(i) Change in state: The physical state of the substances normally changes.

e.g (a) Formation of solid MgO from solid Mg and gaseous O2.(b) Formation of solid Pbl(ppt) from liquid solutions of PbNO3 and Kl.(c) Formation of H2 gas from the reaction of solid Zn with liquid H2SO4.

CHEMICAL REACTIONS AND EQUATIONS

Page # 40 CHEMICAL REACTIONS AND EQUATIONS


(ii) Change in colour : In some of the chemical reactions change in colour can be observed.

e.g. (a) Formation of brown rust on black iron nails.

(b) Formation of yellow ppt. of lead iodide from colourless solution of PbNO3 and Kl.

(iii) Evolution on a gas: In some cases, a gas may be evolved.e.g. (a) Evolution of H2 gas, in the reaction between Zn and dil HCL

(b) Evolution of CO2 gas, during burning of any fuel, which contains carbon.

(iv) Change in temperature: Most of the reactions are accompanied by temperature change. i.e.increase or decrease in temperature.

e.g. (a) In the reaction between Zn and H2SO4, flask was found to be warm. Thus rise intemperature has taken place.

(b) If a reaction between barium hydroxide, Ba(OH)2 and ammonium chloride, NH4Cl is carriedout in a test tube, it is observed that bottom of test tube becomes cooler.

Q. Check Your Concepts

From the given exaples, identify the chemical changes.(a) Fermentation of grapes.

(b) Burning of a candle.

(c) Evaporation of alcohol.

(d) Freezing of water.(e) Turning brown of a freshly cut apple in the air.

(f) Growth of a plant.

(g) Dissolution of sugar in water.

(h) Fading of coloured clothes in the sun.

WORD EQUATIONA chemical equation which represents a chemical reaction briefly in words is called word equation.

Example : For the example the word equation is

Sodium + water Sodium hydroxide + Hydrogen

Reactants:-

Products:-

The substance or substances which takes part in a chemical reaction are called reactants.

The new substance or substances formed as a result of a chemical reaction are called products.

Do You Know?

In the above reaction sodium & water are reactants and sodium hydroxide & hydrogen are products.

RULES FOR WRITING A WORD EQUATION(i) The substances taking part in chemical reaction, reactants are always written on the left hand side

of arrow.(ii) The substances formed after the chemical reaction, products are always written on the right hand

side of arrow.

(iii) A plus sign (+) is put in between the reactants or between the products. If their number is two ormore.

(iv) An arrow ( ) is put between the reactants and products, the arrow shows the direction of thereaction in which the reaction proceeds. The arrow is read as "to yield" or "to form".

In the word equation when symbols and chemical formulae of the reactants and products are

used then it is called as chemical equation.

Example : Na + H2O NaOH + H2



IMPORTANT TERMS AND CONCEPTS

I. Formulae of Ions

1. Valency. The number of electrons shared by an atom is called its valency. It is also called thecombining capacity of an atom, e.g., Cl atom can share one valence electron, its valency is 1, Oxygencan share two valence electrons, its valency is 2. Nitrogen can share 3 valence electrons, its valencyis 3, Carbon can share 4 valence electrons, therefore its valency is 4 and so on.

It means if Carbon combines with Chlorine, Carbon will share four valence electrons with four Chlorineatoms, therefore the molecular formula of the covalent compound will be

i.e. CCl4 is formula.

Some more examples are :

+ 1 Charge Formula + 2 Charge

2+2Hg

Au+

Potassium ion

Manganese (II) ionSb3+

Chromium (III) ion

1 Charge Formula

2 Charge Formula

3 Charge Formula Name of ion Name of ion Name of ion

Bromide ion Chloride ion Fluoride ion Iodide ion

Br Cl F I

Oxide ion Sulphide ion

O2 S2

Nitride ion Phosphide ion Boride ion

N3 P3 B3



*The elements show more than one valency. So a Roman numeral shows theft valency in a bracket.

1 Charge

Name of ionFormula

2 Charge

Name of ion

3HCO

4HSO

3NO

3ClO

2NO

4MnO

2PO

2AlO

+4NH

23CO

24O

23O23O

24O23O

24O

27O

24O

24O

34O

34O

33O

33O33O

Hydrogen carbonate

+1 Charge

Manganate ion

Thiosulphate ion

Phosphate ion

Phosphite ion

Ferricyanide ion

- 4 Charge

[Fe(CN) ]6–4

2. Chemical Equations. “A chemical equation is a symbolic notation that uses formulae of compoundsand symbols of elements to represent a chemical reaction”, e.g., Copper oxide reacts with Carbon toform Copper and Carbon monoxide. The reaction may be represented as

CuO + C Cu + Co

3. Writing of a Chemical Equation.(i) The symbols of elements and the formulae of reacting substances (reactants) are written on the

left hand side and plus (+) sign is written between them.(ii) The symbols and formulae of the substances formed (products) are written on the right hand side

with a plus sign (+) between them.

(iii) An arrow ( ) sign in put between the reactants and products, e. g.,,

Mg + H2SO4 MgSO4 + H2

(iv)The physical states of the reactants and products are also mentioned in a chemical equation.The notations g, l, s, aq. are written in brackets along with symbols/formulae of reactants and products.These symbols stand for gaseous, liquid, solid and aqueous solution respectively, e.g.,

Mg (s) + H2SO4(aq) MgSO4(aq) + H2 (g)

Zn (s) + H2SO

4 (aq) ZnSO

4(aq) + H

2



The symbol ( ) may also be used to represent a gaseous product. The symbol ( ) is used torepresent the formation of a precipitate (water insoluble) or a sparingly soluble substance formedduring the reaction which settles down mostly, e.g.,

NaCl (aq) + AgNO3 (aq) AgCl ( ) + NaNO

3 (aq)

(v) Sometimes, the temperature, pressure and catalyst of the reaction are indicated above and orbelow the arrow in the equation, e.g.,

CO (g) + 2H2 (g) 2 3/340 ,ZnO Cr O

atm heat CH3OH (g)

(vi)A chemical equation represents an actual chemical reaction in which the reactants and productsare known, e.g.,

2 KMnO4 (s) heat

K2MnO4 (s) + MnO2 (s) + O2 (g)

2 KClO3 (s)

2

heatMnO 2 KCl (s) + 3 O

2 (g)

4. Balancing of chemical equation. Observe the following two chemical equations :

Zn + H2SO

4 ZnSO

4 + H

2……(i)

Na + H2O NaOH + H

2…….(ii)

In equation (i), the number of atoms of Zn, H, S, and O are equal on both sides, i.e., the equation isbalanced.

5. Balanced Equations. The equations in which atoms of various elements on the reactant’s and theproduct’s side are equal.Equation (ii) is not balanced because the number of hydrogen atoms is not equal on bothsides. It is called a skeleton chemical equation.

6. Reason of Balancing Equat ions. The number of atoms of elements on both sides of a chemicalequation should be equal in accordance with the law of conservation of mass.

7. Balancing. The process of making atoms of various elements equal in an equation on either side iscalled balancing.

8. Steps in Balancing of Chemical Equations. A number of steps are involved in balancing a chemicalequation, e.g.,

Na + H2O NaOH + H2

Step 1: Examine the number of atoms of different elements present in unbalanced equation.

Number of atoms inreactants

Step 2: Pick an element to balance the equation. In the above equation Na and O are balanced, Hydrogen isnot.

Step : To balance Hydrogen on both sides we need to multiply H2O by 2 which makes Hydrogen atoms equal to4 on the reactants’ side. To make Hydrogen 4 on the products’ side, multiply NaOH by 2. Now oxygenhas become 2 on both sides. But Sodium atom has become two on the product’s side. Multiply Na by 2on the reactant’s side so that they become equal on both sides. The steps are as follows :



(i) Na + 2H2O NaOH + H

2

(ii) Na + 2 H2O 2 NaOH + H2

(iii) 2 Na + 2 H2O 2 NaOH + H2

The equation is now balanced.

Example : Fe + H2O Fe3O4 + H2

Step 1 :Element Number of atoms in

reactants

Step 2 : Pick up the compound which has the maximum number of atoms whether a reactant or a product,and in that compound select the element which has the highest number of atoms, e.g., we selectFe3O4 in the above equation :

To balance oxygen atoms,

In reactant

To equalise the number of atoms, we put the coefficient on the left side of the formula. A coefficient isa small whole number, like coefficients used in algebraic equations. You must keep in mind that we canput coefficients but we cannot change the subscripts in the formula, i.e., to balance Oxygen atoms,we can put the coefficient 4 as 4 H2O and not H2O4 or (H2O)4. Now the partly balanced equationbecomes as follows :

Fe (s) + 4 H2O (g) Fe3O4 (s) + H2 (g) (Partly balanced)

Step 3 : Pick up the second element to balance this partly balanced equation. Let us try to balance hydrogenatoms. bIn partly balanced equation. Atoms of Hydrogen

To equalise the number of Hydrogen atoms, we use 4 as the coefficient of H2 in the products.

Fe (s) + 4H2O (g) Fe3O4 (s) 4H2

Step 4 : Pick up the third element to be balanced. The element which is left to be balanced is Fe.

Atoms of Iron

To equalise iron, we use 3 as coefficient of Fe in reactants.

3 Fe + 4 H2O Fe3O4 + 4H2



Step 5 : Check the correctness of the balanced equation.

Atoms

The equation is balanced because atoms of all the elements are equal on both sides. This method ofbalancing equation is known as hit and trial method.

9. Balancing of Ionic Equations. In these equations, charge balancing is also done along with balancingof atoms on both sides of the equation, e.g.,

Initial Cu2+ (aq) + H2S CuS (s) + H+ (aq).

Balanced Cu2+ (aq) + H2S CuS (s) + 2 H+ (aq)

We have balanced the charges. It was + 2 on LHS and we have made + 2 on RHS. Number of Hydrogenatoms, Cu and Sulphur atoms are also balanced on both sides.

A chemical equation that conserves the amounts of all elements and electrical charges, is said to be balanced.

Do You Know?

Q. Why is it necessary to balance the chemical equation?ExplanationIn order to make law of conservation of mass, applicable on the given chemical equation, it is neces-sary to make number of atoms of all elements equal on L.H.S. & R.H.S. Thus balancing of equation isrequired.

Q. In order to white wash a house a man mixed 10 kg of quick lime with 30 litres of water. Onadding lime, he noticed that the water started boiling even when it was not being heated.Explain what is the reason behind it and write the reaction involved.ExplanationWhen quick lime (CaO) was added to water, formation of slaked lime [Ca(0H)2]has taken place, withthe evolution of a large amount of heat. i.e. its an exothermic reaction, which caused solution to boil.CaO(s) + H2O( ) Ca(OH)2(s) + heatCalcium oxide Calcium hydroxide

In a balanced chemical equation an integer precedes the formula of each substance. This number is known as stoichiometric coefficient.If no number is there, stoichiometric coefficient is taken as 1.

Do You Know?

TYPES OF CHEMICAL REACTIONSThe chemical reactions are classified into various categories depending upon the types of changestaking place. The different types of reactions are as follows :

Chemical Reactions

CombinationReaction

DecompositionReaction

DisplacementReaction

DoubleDisplacementReaction

OxidationandReductionReaction



(i) Combination Reaction. The reactions in which two or more substances combine to form a single newsubstance are called combination reaction.

Combination may take place,

(i) Between two or more elements.

(ii) Between two or more compounds.

(iii) Between elements and compounds.

Some more examples of combination reactions:

(a) Between two elements

(i) Burning of Coal

C(s) + O2(g) CO2(g)

Carbon Oxygen Carbon dioxide

(ii) Formation of Water

2H2(g) + O2(g) 2H2O( )

Hydrogen Oxygen Water

(iii) Burning of Magnesium in air

2Mg(s) + O2(s) 2MgO(s)

Magnesium Oxygen Magnesium oxide

(iv) Formation of Iron sulphide

Fe(s) + S(s) FeS(s)

Iron Sulphur Iron sulphide

(b) Between 2 compounds

(i) Formation of Ammonium chloride

NH3(g) + HCl(g) NH4Cl(s)

Ammonia Hydrogen Ammonium

Chloride Chloride

(ii) Formation of Calcium Carbonate

CaO(s) + CO2(g) CaCO3(s)

Calcium oxide Carbon Calcium

(Quick lime) dioxide carbonate

(c) Between an element and a compound

(i) Reaction of carbon monoxide with oxygen

2CO(g) + O2(g) 2CO2(g)

This is also an exothermic reactions.

Q. How the process of respiration help us to stay alive?

Explanation

The food we eat provides us the energy to stay alive. During digestion, food is broken down intosimpler substances. For example, rice, potatoes and bread contain carbohydrates. Thesecarbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of ourbody and provides energy. The special name of this reaction is respiration.

C6H12O6(aq) + 6O2(aq) 6O2(aq) + 6H2O( ) + energy

Glucose Oxygen Carbon dioxide Water

So, we can say that respiration is an exothermic reaction.



ACTIVITY - 1

Aim : To show the combination reaction between calcium oxide and water is an exothermicprocess.

Materials Required: Quicklime (calcium oxide), water, beaker.

Procedure :

1. Take 5 g of calcium oxide in a beaker.

2. Add water to it slowly.

3. Touch the beaker.

4. Note down the observations.

Observation : Calcium oxide reacts with water vigorously

to form calcium hydroxide with the evolution of heat.

Chemical Reaction :

CaO (s) + H2O (l) Ca(OH)2 (aq) + Heat

Conclusion : The reaction between CaO (Calcium oxide) and

H2O is a combination reaction. It is an exothermic process because heat is evolved.

ACTIVITY - 2

Aim: To show burning of magnesium ribbon in air is a combination reaction.

Materials Required: Magnesium wire, tongs, burner.

Procedure :

1. Take a strip of magnesium ribbon and hold it with the

help of tongs.

2. Introduce it in the flame of the burner.

Observation : Magnesium ribbon bums with dazzling light

and white substance is formed which is magnesium oxide.

This happens due to following chemical reaction.

Chemical Reaction :

2 Mg (s) + O2 (g) 2 MgO (s)

Conclusion : Burning of magnesium in presence of oxygen to form magnesium oxide is acombination reaction.

(ii) Decomposition Reaction. A reaction in which a single compound breaks down to produce two ormore simpler substances. i.e., a compound decomposes into simpler substances.

It is opposite to combination reactions.

There are three ways in which decomposition reactions can be carried out, i.e., energy required indecomposition reaction can be supplied in the following ways:(i) Heat (ii) Electricity (iii) Light

(1)Electrolysis. When decomposition reaction is carried out with the help of electric current, theprocess is called electrolysis (‘electro’ means electric, ‘lysis’ means break down), e.g., when electriccurrent is passed through acidified water (water mixed with a few drops of acid so as to make it agood conductor), it decomposes into Hydrogen and Oxygen gases.

2 H2O (l) electric current

2 H2 (g) + O2 (g)



ACTIVITY - 3

Aim : To demonstrate electrolysis of water.

Materials Required : Plastic mug, drilling machine or screw driver, carbon electrodes, 6 voltbattery, dil. H

2SO

4, water

Procedure :1. Take a plastic mug.2. Drill two holes at the base and insert carbon electrodes as shown in figure.3. Fill the mug with water to its half and add a few drops of dilute sulphuric acid.4. Fill a graduated measuring cylinder with water and invert it in the apparatus so that one of

the two electrodes is enclosed within it.5. Fill another graduated cylinder with water and invert it over the second electrode.6. Allow the current to pass through the voltameter and leave the apparatus undisturbed for

some time.7. The bubble formation starts at both the electrodes.8. Observe the volume of gases collected in the inverted measuring cylinders.9. Collect the gases in respective cylinders and test them separately.10. Bring a match stick near each of the gases in the cylinders and note down the observation

and write conclusion about the gas.

6 VBattery

Hydrogen

Water

Water

Plastic Mug

Test tubeOxygen

Anode

Switch

CathodeRubber stopper

Graphfite rod

Electrolysis of Water

Observation : The volume of one of the gases is twice the volume of other gas. One of thegases catches fire and burns with ‘pop’ sound whereas in other gas match stick burns brightly.

Conclusion : Water, on electrolysis decomposes to hydrogen gas and oxygen gas. Hydrogen gasburns explosively whereas oxygen gas helps in burning, i.e., hydrogen is highly combustible andoxygen is supporter of combustion.

(2) Thermal Decomposition. When decomposition reaction is carried out by heating, it is calledthermal decomposition reaction, e.g.,

CaCO3 (s) heat

CaO (s) + CO2 (g)

[Limestone] [Quick lime]

FeSO4 (S) heat Fe2O3 + SO2(g) + SO3(g)

[Ferric oxide]

2Pb(NO3)2(S) heat 2PbO + 4NO2(g) + O2(g)

Zn CO3 (s) heat

ZnO (s) + CO2 (g)

The process of heating ZnCO3 (Calamine), an ore of zinc in absence of air to form Zinc oxide (ZnO) andCO (g) is also called calcination.



ACTIVITY - 4Aim : To show heating of lead nitrate is decomposition reaction.

Materials Required : A test tube, lead nitrate solid.

Procedure :1. Take lead nitrate (white powder) in a test tube and hold

it in tongs.2. Heat it over flame of burner slowly as shown in diagram.

Observation : Pungent smelling brown fumes are evolved and brownish residue is left.

Chemical Reaction :

2 Pb(NO3)2 heat

2PbO (s) + 4 NO2 (g) + O2 (g)

Explanation : Lead nitrate on heating decomposes to lead monoxide (brown), brown gas nitrogendioxide (NO2) and oxygen gas are evolved.Conclusion : It is an example of decomposition reaction.

ACTIVITY - 5

Aim : To show decomposition reaction of ferrous sulphate.

Materials Required : Ferrous sulphate crystals, dry test tube, burner.

Procedure :1. Take 2 g of ferrous sulphate crystals in a dry test tube.2. Observe the colour of ferrous sulphate crystals.3. Heat the crystals of ferrous sulphate over the flameof a

burner for some time. 4. Observe the crystals after heating for 5 minutes.

Observation : The green colour of ferrous sulphate crystalschanges to brownish black ferric oxide and smell of burning sulphur is observed.Chemical Reaction :

2 FeSO4 (s) heat

Fe2O3 (s) + SO2 (g) + SO3 (g)

Explanation : Ferrous sulphate decomposes to form ferric oxide along with evolution of SO2 andSO3 gases.Conclusion : Heating of ferrous sulphate is a thermal decomposition reaction because ferroussulphate breaks down into simpler compounds Fe2O3, SO2 and SO3.

The decomposition of vegetable matter into compostis also an example of an exothermic reaction.

Do You Know?

(3) Photochemical Decomposition :Chemical reaction in which a compound decomposes into simpler substances on the absorption oflight energy is called photo-decomposition reaction.

2Agcl(s) sunlight 2Ag(s) + Cl2(g)

Silver Chloride Silver(White) (Grey in colour)

2AgBr(s) sunlight 2Ag(s) + Br2(g)

Silver Bromide Silver BromineThe Decomposition of a Compound with light is called “Photolysis.”All Decomposition reaction requires energy i.e. these reactions are “Endothermic reactions.”These reactions are used in extractions of metals.



ACTIVITY - 6

Aim : To show photochemical decomposition of silver chloride.

Materials Required : AgNO3 (aq), NaCl (aq), test tubes.

Procedure :

1. Take 5 ml of silver nitrate solution in a test tube.

2. Prepare sodium chloride solution in another test tube.

3. Add sodium chloride solution into test tube containing

silver nitrate solution.

4. Observe the colour of silver chloride formed. Dry it with the

help of filter papers and place it on the watch glass.

5. Place the watch glass under sunlight for some time.

6. Observe the colour of the silver chloride after some time.

Observation : White silver chloride turns grey in sunlight because silver metal is formed.

Chemical Reaction :

2 AgCl (s) sunlight

2 Ag(s) + Cl2 (g)

Explanation : Silver chloride is photo-sensitive. It decomposes in presence of sunlight to form

silver metal and chlorine gas.

Conclusion : Decomposition of silver chloride in presence of sunlight is photochemical decomposition

reaction.

Other examples of photochemical reactions : Silver bromide and silver iodide also decompose

in the same manner.

2 AgBr (s) sunlight

2 Ag(s) + Br2 (g)

2 AgI (s) sunlight

2 Ag (s) + I2 (g)

These reactions are photochemical reactions which are used in black and white photography. Anotherimportant example of decomposition reaction in our body is digestion of food. When we eat rice, wheat

or potatoes, the starch gets decomposed to simple sugar and proteins get converted into simplesubstances called amino acids in our body.

(C6H10O5)n + H2ODiastase

C12H22O11

C12H22O11 + H2OMaltase

2C6H12O6

Proteins Pep sin Amino acids

We have observed all the decomposition reactions require energy either in form of heat, light or

electricity for breaking down of reactants. Therefore, they are endothermic reactions.

Endothermic Reactions: Those reactions in which heat is absorbed are called endothermic reactions.

Decomposition reaction is just opposite of the combination reaction.

Do You Know?



DecompositionReactions

Thermaldecomposition

reaction

Electrodecomposition

reaction

Photodecomposition

reaction

Absorptionof heat

Memory Tip

(iii) Displacement Reactions. Those reactions in which a more reactive element displaces a less reactiveelement from a compound are called displacement reactions.

Potassium K Most Reactive

Sodium Na

Barium Ba

Calcium Ca

Magnesium Mg

Aluminium Al

Zinc Zn

Iron Fe

Nickel Ni

Tin Sn

Lead Pb

Hydrogen H

Copper Cu

Mercury Hg

Silver Ag

Gold Au Least Reactive

These reactions mostly occur in solution form, e.g.,

Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)

Colourless Reddish brown

Pb + CuSO4 (aq) PbSO

4 + Cu (s)

It is a displacement reaction. Other examples are :

Mg + CuSO4 MgSO4(aq) + Zn (s)



It shows magnesium is more reactive than Cu because it can displace Copper from Copper sulphate

solution.

Mg(s) + ZnSO4 (aq) MgSO4 (aq) + Zn (s)

Mg (s) + FeSO4 (aq) MgSO4 (aq) + Fe (s)

These reactions show that Mg is more reactive than Zn and Fe.

Zn (s) + FeSO4 (aq) ZnSO4 (aq) + Fe (s)]

It shows Zn is more reactive than Fe.

On the basis of the above reactions, we can conclude Mg > Zn >Fe > Pb > Cu > Ag is the order of

reactivity.

Zn (s) + H2SO4 (dil.) ZnSO4 (aq) + H2 (g)

Mg (s) + H2SO4 (dil.) MgSO4 (aq) + H2 (g)

These reactions show that Zn and Mg are more reactive than Hydrogen because they displace Hydrogen

from dilute acids. These are also examples of displacement reactions.

ACTIVITY - 7

Aim: To show iron is more reactive than copper.

Materials Required : Iron nails, copper sulphate

solution, test tubes.

Procedure :

1. Take blue coloured copper sulphate solution

in a test tube.

2. Put iron nails in it.

Observation : Colour of solution slowly changes to

light green and brown coloured copper metal gets

deposited over iron nails.

Chemical Reaction :

Fe (s) + CuSO4 (aq) heat

FeSO4 (aq) + Cu (s)

Blue Light green

Conclusion : Iron is more reactive than copper because iron can displace copper from copper

sulphate solution. It is an example of displacement reaction.



ACTIVITY - 8

\ Aim : To show the displacement reaction between zinc granules

and dilute hydrochloric ac id or dilute sulphuric acid.

Materials Required : Zinc granules, conical flask,

dil. HCl or dil. H2SO4.

Procedure :

1. Take 5-6 zinc granules in a conical flask.

2. Set the apparatus as shown in figure.

3. Add dil. HCl or dil. H2SO4 over it.

4. Observe the reaction.

5. Touch the conical flask and observe the change in

temperature.

Observation: The bubbles of hydrogen gas are observed.

The conical flask becomes hot showing that the process is exothermic.

Chemical Reaction :

Zn (s) + 2 HCl (dil) ZnCl2 (aq) + H2 (g)

Zn (s) + H2SO4 (dil) ZnSO4 (aq) + H2 (g)

Conclusion : The reaction between Zn and dil. HCl or dil. H2SO4 is a displacement reaction.

It is exothermic process. It shows zinc is more reactive than hydrogen, therefore it can displace

hydrogen from dilute acids like HCl and H2SO4.

(iv) Double Decomposition Reactions (Double Displacement Reactions). Those reactions in which

two different atoms or groups of atoms are displaced by other atoms or groups of atoms, i.e., two

compounds exchange their ions and one of the products formed is insoluble, e.g.,

BaCl2 (aq) + Na2SO4 (aq) BaSO4 (s) + 2NaCl (aq)

Here, S 24O ions are displacing Cl ions and Cl ions are displacing S 2

4O ions. Since it involves

displacement of two species, therefore, is called double displacement reactions.

If one of the products formed in the reaction is insoluble, it is also called double decomposition

reaction.

These reactions usually occur in between ionic compounds when they are dissolved in water i.e., in

aqueous solution.

These reactions are fast reactions and take place within fraction of a second.



Other examples of double displacement reactions are

AgNO3 (aq) + NaBr (aq) AgBr + NaNO3 (aq)

AgNO3 (aq) + KI (aq) AgI + KNO3 (aq)

FeSO4 (aq) + 2 NaOH (aq) Fe (OH)2 + Na2SO4 (aq)

Cr2(SO4)3 + 6 NaOH 2 Cr(OH)3 + 3 Na2SO4 (aq)

FeCl3 + 3 NaOH Fe(OH)3 + 3 NaCl (aq)

AlCl3 + 3 NaOH Al(OH)3 + 3 NaCl (aq)

CuSO4 + H2S(g) CuS + H2SO4 (aq)

MnSO4

+ H2S (g) MnS + H

2SO

4 (aq.)

NiCl2 + H2S (g) NiS + 2 HCl (aq)

Pb (NO3)2 + 2 HCl (aq) PbCl2 (s) + 2 HNO3 (aq)

CaCO3 + 2 NaCl (aq) CaCl2 (aq) + Na2CO3(aq)

Ca(NO3)2 + (NH4)2 CO3 CaCO3 + 2 NH4NO3

ZnSO4 + H2S ZnS + H2SO4 (aq)

ACTIVITY - 9

Aim : To show reaction between sodium sulphate solution and barium chloride solution is double

displacement reaction (precipitation reaction).

Materials Required : Barium chloride solution, sodium sulphate solution, two test tubes.

Procedure :

1. Take sodium sulphate solution in a test tube.

2. Add few drops of solution of barium chloride.

Observation : White precipitate is formed.

Chemical Reaction :

Na2SO4 (aq) + BaCl2 (aq) BaSO4 + 2NaCl (aq)

Conclusion : Reaction between sodium sulphate solution and barium chloride solution is

double displacement reaction.



ACTIVITY - 10

Aim : To show the reaction between lead nitrate and potassium iodide is double decomposition

reaction (precipitation reaction).

Materials Required : Test tubes, lead nitrate solution, potassium iodide solution.

Procedure :

1. Take lead nitrate solution in a test tube.

2. Add potassium iodide solution to it.

3. Observe the changes taking place in the solution.

Observation : Yellow precipitate is formed.

Chemical Reaction and Explanation : Lead nitrate reacts with potassium iodide to form lead

iodide which is insoluble in water and yellow in colour. It is called precipitate. The reaction is also

called precipitation reaction.

Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2 KNO3 (aq)

Conclusion : The reaction between lead nitrate and potassium iodide is double decompositionreaction. Since Pb is insoluble called precipitate, therefore, this reaction is also called precipitationreaction.

(v) Neutralization Reactions. Those reactions in which acid or acidic oxide reacts with base or basicoxide to form salt and water are called neutralization reactions, e.g.,

NaOH + HNO3 NaNO3 + H2O

2 NaOH + H2SO4 Na2SO4 + 2 H2O

KOH + HCl KCl + H2O

KOH + HNO3 KNO3 + H2O

2KOH + H2SO4 K2SO4 + 2H2O

CH3COOH + NaOH CH3COONa + H2O

+ 2NaOH + 2H2O

When salt of weak acid reacts with strong acid, it is also called neutralization reaction.

Na2CO3 + 2HCl 2NaCl + H2O + CO2

CH3COONa + HCl CH3COOH + NaCl

When acidic salt reacts with base to form salt and water, it is also called neutralization reaction.

NaHCO3 + NaOH Na2CO3 + H2O



(vi) Oxidation and Reduction(1) Oxidation.

(a) It is a process in which Oxygen or an electronegative element is added.(b) It can also be defined as a process in which Hydrogen or an electropositive element is removed.(c) In terms of electronic concept, oxidation is a process in which loss of electrons takes place.

4Na + O2 2 Na2O (Addition of oxygen)

2Mg + O2 2 MgO (Addition of oxygen)

Fe2+ Fe3+ + e (Loss of electron)

2 Fe + 3 Cl2 2 FeCl3 (Addition of electronegative element)

Hg2Cl2 Hg + HgCl2 (Removal of electropositive element)

CH3CH2OH 300oCu

C CH3CHO + H2 (Removal of Hydrogn)

(2) Reduction.

(a) It is a process in which addition of Hydrogen or an electropositive element takes place.(b) It is also defined as a process in which Oxygen or an electronegative element is removed.(c) In electronic concept, reduction process involves gain of electrons.

2 Na + H2 2NaH (Addition of Hydrogen)

CuO + H2 Cu + H2O (Removal of Oxygen and addition of hydrogen)

Fe3+ + e Fe2+ (Gain of electron)

Hg + HgCl2 Hg2Cl2 (Addition of an electropositive element)

Cu + CuCl2 Cu2Cl2 (Addition of an electropositive element)

AuCl3 AuCl + Cl2 (Removal of an electronegative element)

ACTIVITY - 11

Aim: To study oxidation of copper to copper (II) oxide.

Method: Heat a china dish containing about 1 9 copper powder .

Now answer: What do you observe?

Discussion: It is observed that the brown copper powder gets coated with black copper (II)oxide.

Wire gauze

Tripod stand

Burner

Oxidation of copper to copper oxide



Conclusion:

Copper (brown in colour) on heating combines with oxygen to form black copper (II) oxide.

2Cu(s) + O2(g) 2CuO(s)

Copper(Brown) Oxygen Copper (II) oxide (Black)

Here, we can say that copper is being oxidised, as it is gaining oxygen. In the above activity ifhydrogen gas is passed over product (CuO) and the black coating on the surface becomesbrown because reverse reaction takes place.

CuO(s) + H2(g) Heat Cu(s) + H2O( )

Here, we can say that copper oxide is being reducing, as it is loosing oxygen and hydrogen isbeing oxidised.

Redox Reactions : Those reactions in which oxidation and reduction take place simultaneously arecalled redox reactions, e.g.,

(i)

Mn4+ + 2e Mn2+ (Reduction) [Gain of electrons]

2 Cl Cl2 + 2e (Oxidation) [Loss of electron]

(ii) Cu (s) + I2 (s) CuI2 (s)

Cu (s) Cu2+ (aq) + 2e (Oxidation) [Loss of electron]

I2 (s) + 2e 2I (Reduction) [Gain of electron]

Cu (s) + I2 (s) CuI

2 + 2e

Cu (s) + I2 (s) CuI2 (s) is a Redox reaction.

Oxidising Agent. It is a substance which can

(i) add oxygen or an electronegative element to other materials.

(ii) remove hydrogen or an electropositive element from other materials.

(iii) gain electrons.

Oxidising agent itself gets reduced.

Reducing Agent. It is a substance which can

(i) add hydrogen or an electropositive element to other materials.

(ii) remove oxygen or an electronegative element from other materials

(iii) lose electrons.

Reducing agent itself gets oxidised.



Example 1. Fe + S FeS

Fe Fe2+ + 2e (Oxidation)

S + 2e S2 (Reduction)

Fe is losing electrons, therefore, it acts as a Reducing agent.

S is gaining electrons, therefore, it acts as an Oxidising agent.

Fe is getting oxidised to Fe2+ (Ferrous ion) whereas S gets reduced to S2 (Sulphide ion)

Example 2. Cu (s) + 2AgNO3 (aq) Cu (NO3)2 (aq) + 2 Ag (s)

Cu (s) Cu2+ + 2e (Oxidation)

2 Ag+ + 2e 2 Ag (Reduction)

Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag (s)

Cu is a reducing agent because it is losing electrons whereas Ag+ is an oxidising agent.

Example 3.

Fe2O3 is an oxidizing agent whereas Al is a readucing agent.

Example 4. Zn + CuSO4 ZnSO4 + Cu

Zn is a reducing agent whereas Cu2+ is an oxidizing agent

Example 5. 2 Na + Cl2 2NaCl

2 Na 2 Na+ + 2e [Oxidation]

Cl2 + 2e 2Cl

Na is a reducing agent whereas Cl2 is an oxidizing agent.

Example 6.

H2S is a reducing agent whereas SO2 is an oxidizing agent.



ChemicalReaction

Reductionreaction

Decompositionreaction

Combinationreaction

Oxidationreaction

Double displacementreaction

Displacementreaction

Memory Tip

EFFECTS OF OXIDATION IN EVERYDAY LIFE

Oxidation has damaging effect on metals as well as on food. The damaging effect of oxidation on

metals is studied as corrosion and that on food is studied as rancidity.

Thus there are two common effects of oxidation reactions are as

(I) Corrosion of metals (II) Rancidity of food

(I) Corrosion of metals :– Corrosion is the process of deterioration of metals as a result of its reaction

with air, moisture and acids. (Present in environment) surrounding it.

The corrosion causes damage to buildings, bridges, ships and many other articles especially made of iron.

Rust : Iron corrode readily when exposed to moisture and gets covered with a brown flaky substance

called rust. It is called rusting of iron, Rust is a hydrated Iron (III) oxide. [Fe2O3 · 2H2O]

Oil

Iron nailIron nail

Boiledwater

RustTap water

Iron nail

Dry waterAnhydrous

calcium chloride (a) (b) (c)

Rusting of iron takes place under the following conditions –

(a) Presence of air (or oxygen)

(b) Presence of water (or moisture) It has been observed that

(c) Presence of impurities in the metal speed up the rusting process. Pure iron does not rust.

(d) Presence of electrolytes in water also speeds up the process of rusting

(e) The position of the metal in the electrochemical series determines the extent of corrosion. More

the reactivity of the metal, there will be more possibility of the metal getting corroded.



Other examples of corrosion are –

(i) Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brownsurface and acquires a green coating of basic copper carbonate.

(ii) Silver articles become black after sometime when exposed to air because it reacts with

sulphur to form a coating of silver sulphide.

(iii) Lead or stainless steel lose their lusture due to corrosion.

(iv) Unreactive metals such as Gold, Platinum, Palladium, Titanium etc. do not corrode.

Prevention of Rusting.

1. The iron articles should be painted.

2. The machine parts should be oiled and greased.

3. Galvanised iron pipes are used for water supply.

4. Iron can be coated with chromium to prevent rusting.

(II) Rancidity. The oxidation of oils or fats in food, resulting into a bad taste and bad smell is called

rancidity. It is caused due to prolonged exposure of food in air. Oxygen present in air oxidise fats/oilpresent in food and form volatile substances, which have bad odour.

Vitamin E and Vitamin C (Ascorbic acid) arethe two antioxidants occuring in natural fats.

Do You Know?

Prevention of rancidity :–

(i) Rancidity can be prevented by adding antioxidants to foods containing fats and oils. Antioxidantsare reducing agents so when they are added to food it do not get oxidised easily and hence do notturn rancid. The two common anti oxidants are –

(a) BHA (Butylated Hydroxy Anisole)

(b) BHT (Butylated Hydroxy Toluene)

(ii) Rancidity can be prevented by packaging fat and oil containing foods in nitrogen gas.

(iii) It can be retarted by keeping food in refrigerator.

(iv) It can also be retarded by storing food in air tight containers.

(v)It can be retarded by storing foods away from light.



Ex.1 Translate the following statements into chemical equations and then balance them.

(A) Hydrogen gas combines with nitrogen to form ammonia

(B) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

(C) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of bariumsulphate.

(D) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Sol. (A) N2(g) + 3H2(g) 2NH3(g)

(B) 2H2S + 3O2 2H2O + 2SO2

from air

(C) 3BaCl2(aq) + Al2(SO4)3(aq) 2AlCl3(aq) + 3BaSO4(s)

White ppt.

(D) 2K(s) + 2H2O(l) 2KOH + H2(g)

Ex.2 Balance the following chemical equations.

(A) HNO3 + Ca(OH)2 Ca(NO3)2 + H2O

(B) NaOH + H2SO4 Na2SO4 + H2O

Sol. (A) 2HNO3 + Ca(OH)2 Ca(NO3)2 + 2H2O

(B) 2NaOH + H2SO4 Na2SO4 + 2H2O

Ex.3 Write the balanced chemical equations for the following reactions.

(A) Calcium hydroxide + Carbon dioxide Calcium carbonate + water

(B) Zinc + Silver nitrate Zinc nitrate + Silver

(C) Aluminium + copper chloride Aluminium chloride + Copper

(D) Barium chloride + Potassium sulphate Barium sulphate + Potassium chloride.

Sol. (A) Ca(OH)2 + CO2 CaCO3 + H2O

calcium carbon calcium

hydroxide dioxide carbonate

(B) Zn + 2AgNO3 Zn(NO3)2 + 2Ag

zinc silver nitrate zinc nitrate silver

(C) 2Al + 3CuCl2 2AlCl3 + 3Cu

aluminium copper aluminium copper

chloride chloride

(B) BaCl2 + K2SO4 BaSO4 + 2KCl

barium potassium barium potassium

chloride sulphate sulphate chloride

SOLVED PROBLEMS



Ex.4 Write the balanced chemical equation for the following and identify the type of reaction in each case

(A) Potassium bromide(aq) + Barium iodide(aq) Potassium iodide(aq) + Barium bromide(s)

(B) Zinc carbonate (s) Zinc oxide (s) + Carbon dioxide(g)

(C) Hydrogen(g) + Chlorine(g) Hydrogen chloride(g)

(D) Magnesium(s) + Hydrochloridc acid(aq) Magnesium chloride(aq) + Hydrogen(g)

Sol. (A) 2KBr(aq) + BaI2(aq) 2KI(aq) + BaBr2(aq)

This reaction is a double-displacement reaction.

(B) ZnCO3(s) ZnO(s) + CO2(g)

This reaction is a decomposition reaction

(C) H2(g) + Cl2(g) 2HCl(g) [Combination Reaction]

(D) Mg(s) + 2HCl(aq.) MgCl2(aq.) + H2(g) [Displacement Reaction]

Ex.5 Why should a magnesium ribbon be cleaned before burning in air?

Sol. Magnesium reacts with the constituent gases of the atmosphere to form various compounds which get

deposited over its surface. The ribbon is cleaned before burning to remove the layer of these compounds

so that pure magnesium can burn in air.

Ex.6 In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by

copper metal. Write down the reaction involved.

Sol. 2AgNO3(aq) + Cu(s) 2Ag(s) + Cu(NO3)2(aq)

(silver nitrate) (copper) (silver metal) (copper(II) nitrate)

Ex.7 A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and

the black coloured compound formed.

Sol. An element on heating in air changes in its oxide. The brownish element which forms black oxide is

copper. So,

Name of the element Copper (Cu)

Name of black compound: Copper(II) oxide, (CuO)

Reaction 2Cu(s) + O2(g) Heat 2CuO(s)

copper (brown) from air copper(II) oxide (black)



Ex.8 What happens chemically when quick lime is added or water ?

Sol. Calcium hydroxide (or slaked lime) is formed accompanied by a hissing sound. So much heat is evolvedduring the reaction that the reaction mixture starts boiling. The chemical equation for the reactionis :

CaO(s) + H2O(aq) Ca(OH)2(s) + heat

(Quick lime) (Slaked lime)

Ex.9 What is an oxidation reaction ? Identify in the following reactions :

(i) the substance oxidised (ii) the substance reduced.

ZnO + C Zn + CO

Sol. Oxidation involves the addition of oxygen or the removal of hydrogen in a chemical reaction whilereduction involves the addition of hydrogen or removal of organ.

In the given reaction :

(i) Carbon (C) is oxidised to carbon monoxide (CO).

(ii) Zinc oxide (ZnO) is reduced to zinc (Zn)

Ex.10 Which gas is evolved when dilute hydrochloric acid reacts with zinc ? Write the molecular formulaof the gas.

Sol. Hydrogen gas is evolved. Its molecular formula is H2.

Ex.11 State any two observation in an activity which may suggest that a chemical reaction has takenplace. Give examples in support of your answer.

Sol. (i) In a tube take small amount of solid sodium carbonate (Na2CO3). To this add a few drops ofhydrocloric acid.

(ii) A colourless and odourless gas will evolve which shows that a chemical reaction has taken place.The gas will turn lime water milky when passed through it.



Ex.12 Identify the type of reaction in the following examples :

(i) Na2SO4(aq) + BaCl2(aq) BaSO4(s) + 2NaCl(aq)

(ii) Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

(iii) 2H2(g) + O2(g) 2H2O( )

Sol. (i) It is an example of double displacement reaction.

(ii) It is an example of displacement reaction.

(iii) It is an example of combination reaction.

Ex.13 Solid calcium oxide was taken in a container and water was added slowly to it

(i) State two observations made in the experiment.

(ii) Write the name of the chemical formula of the product.

Sol. (i) Water will start boiling and hissing noise will be produced.

(ii) Calcium hydroxide (slaked lime) will be formed.

CaO(s) + H2O(aq) Ca(OH)2(s) + heat

Calcium oxide Calcium hydroxide

Ex.14 A house wife wanted her house to be white washed. She bought 10 kg of quick lime from the

market and dissolved in 30 litres of water. On adding lime to water, she noticed that the waterstarted boiling even when it was not being heated. Give reason for her observation. Write thecorresponding equation and name the product formed.

Sol. A supension of slaked lime also called calcium hydroxide is formed when water is added to quicklime.

CaO(s) + H2O( ) Ca(OH)2(s) + heat

(Slaked lime)

Since the reaction is highly exothermic, the solution started although it was not being heated.The suspension of slaked lime is allowed to cool for sometime, preferably overnight. It is then decantedand the liquid obtained is used for white washing.



NCERT QUESTIONS WITH SOLUTIONSQ.1 Why should a magnesium ribbon be cleaned before it is burnt in air?Ans. Magnesium is an extremely reactive metal. When stored, it reacts with oxygen to form a layer of

magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents furtherreaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper for removing thislayer so that the underlying metal can be exposed to air.

Q.2 Write the balanced equation for the following chemical reactios.

(i) Hydrogen + Chlorine Hydrogen chloride

(ii) Berium chloride + Aluminium sulphate Barium sulphate + Aluminium chloride

(iii) Sodium + Water Sodium hydroxide + Hydrogen

Ans. (i) H2(g) + Cl2(g) 2HCl(g)

(ii) 3BaCl2(aq) + Al2(SO4)3(aq) 3BaSO3(s) + 2AlCl3(aq)(iii) 2Na(s) + 2H

2O( ) 2NaOH(aq) + H

2(g)

Q.3 Write a balanced chemical equation with state symbols for the following reactions.

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphateand the solution of sodium chloride.

(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) reacts withhydrochloric acid solution (in water) to produce sodium chloride solution and water.

Ans. (i) BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

(ii) NaOH(aq) + HCl(aq) NaCl(aq) + H2O( )

Q.4 A solution of a substance 'X' is used for white washing.

(i) Name the substance 'X' and write its formula.

(ii) Write the reaction of the substance 'X' with water.Ans. (i) The substance 'X' is calcium oxide. Its chemical foluma is CaO.

(ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).

CaO(s) + H2O( ) Ca(OH)2(aq)

Calcium oxide Water Calcium hydroxide (Quick lime) (Slaked lime)

Q.5 Why is the amount of gas collected in one of the test tubes is double of the amount collected in theother? Name this gas.

Ans. Water (H2O) contains two parts hydrogen and one part oxygen. Therefore, the amount of hydrogenand oxygen produced during electrolysis of water is in a 2 : 1 ratio. During electrolysis, since hydrogengoes to one test tube and oxygen goes to another, the amount of gas collected in one of the testtubes is double of the amount collected in the other.

Q.6 Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Ans. When an iron nail is placed in a copper sulphate solution, iron displaces copper from copper sulphatesolution forming iron sulphate, which is green in colour.

Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)Iron Copper sulphate Iron sulphate Copper

(Blue colour) (Green colour)

Therefore, the blue colour of copper sulphate solution fades and green colour appears.



Q.7 Give an example of a double displacement reaction other than the one given in Activity 1.10.

Ans. Sodium carbonate reacts with calcium chloride to form calcium carbonate and sodium chloride.

Na2CO3(aq) + CaCl2(aq) CaCO3(s) + 2NaCl(aq)

Sodium Calcium Calcium Sodium

carbonate chloride carbonate chloride

In this reaction, sodium carbonate and calcium chloride exchange ions to form two new compounds.Hence, it is a double displacement reaction.

Q.8 Identify the substances that are oxidised and the substances that are reduced in the followiingreactions.

(i) 4Na(s) + O2(g) 2Na2O(s) + O2(g)

(ii) CuO(s) + H2(g) Cu(s) + H2O( )

Ans. (i) Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.

(ii) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidised to water (H

2O).

Q.9 Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) 2Pb(s) + CO2(g)

(a) Lead is getting reduced.

(b) Carbon dioxide is getting oxidised.

(c) Carbon is getting oxidised.

(d) Lead oxide is getting reduced.

(1) (a) and (b) (2) (a) and (c) (3) (a), (b) and (c) (4) all

Ans. (1) (a) and (b)

Q.10 Fe2O3 + 2Al Al2O3 + 2Fe

The above reaction is an example of a

(1) Combination reaction. (2) Double displacement reaction.

(3) Decomposition reaction. (4) Displacement reaction.

Ans. (4) The given reaction is an example of a displacement reaction.

Q.11 What happens when dilute hydrochloric add is added to iron filings? Tick the correct answer.

(1) Hydrogen gas and iron chloride are produced.

(2) Chlorine gas and iron hydroxide are produced.

(3) No reaction takes place.

(4) Iron salt and water are produced.

Ans. (1) Hydrogen gas and iron chloride are produced. The reaction is as follows:

Fe(s) + 2HCl(aq) FeCl2(aq) + H2

Q.12 What is a balanced chemical equation? Why should chemical equations be balanced ?

Ans. A reaction which has an equal number of atoms of all the elements on both sides of the chemicalequation is called a balanced chemical equation. The law of conservation of mass states that mass canneither be created nor destroyed. Hence, in a chemical reaction, the total mass of reactants should,be equal to the total mass of the products. It means that the total number of atoms of each elementshould be equal on both sides of a chemical equation. Hence, it is for this reason that chemicalequations should be balanced.



Q.13 Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.

(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate ofbarium sulphate.

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Ans. (a) 3H2(g) + N

2(g) 2NH

3(g)

(b) 2H2S(g) + 3O2(g) 2H2O( ) + 2SO2(g)

(c) 3BaCl2(aq) +Al2(SO4)3 (aq) 2AlCl3(aq) + 3BaSO4(s)

(d) 2K(s) + 2H2O( ) 2KOH(aq) + H2(g)

Q.14 Balance the following chemical equations.

(a) HNO3 + Ca(OH)2 Ca(NO3)2 + H2O

(b) NaOH + H2SO4 Na2SO4 + H2O

(c) NaCl + AgNO3 AgCl + NaNO3

(d) BaCl2 + H

2SO

4 BaSO

4 + HCl

Ans. (a) 2HNO3 + Ca(OH)2 Ca(NO3)2 + H2(g)

(b) 2NaOH + H2SO4 Na2SO4 + 2H2O

(c) NaCl + AgNO3 AgCl + NaNO3

(d) BaCl2+ H2SO4 BaSO4 + 2HCl

Q.15 Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxide Calcium carbonate + Water

(b) Zinc + Silver nitrate Zinc nitrate + Silver

(c) Aluminium + Copper chloride Alumiium chloride + Copper

(d) Barium chloride + Potassium sulhate Barium sulphate + Potassium chloride

Ans. (a) Ca(OH)2 + CO2 CaCO3 + H2O

(b)Zn + 2AgNO3 Zn(NO3)2 + 2Ag

(c) 2Al + 3CuCl2 2AlCl3 + 3Cu

(d) BaCl2 + K2SO4 BaSO4 + 2KCl

Q.16 Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium iodide(aq) + Barium iodide(aq) Carbon dioxide(g)

(b) Zinc carbonate(s) Zinc oxide(s) + Carbon dioxide(g)

(c) Hydrogen(g) + Chlorine(g) Hydrogen chloride(g)

(d) Magnesium(s) + Hydrochloric acid(aq) Magnesium chloride(aq) + Hydrogen(g)

Ans. (a) 2KBr(aq) + BaIz(aq) 2KI(aq) + BaBr2(s); Double displacement reaction

(b) ZnCO3(s) ZnO(s) + CO2(g) ; Decomposition reaction

(c) H2(g) + Cl

2(g) 2HCl(g) ; Combination reaction

(d) Mg(s) + 2HCl(aq) MgCl2(aq) + H

2(g) ; Displacement reaction



Q.17 What does one mean by exothermic and endothermic reactions? Give examples.

Ans. Chemical'reactions that release energy in the form of heat, light, or sound are called exothermicreaction.

Example: Mixture of sodium and chlorine to yield table salt

Na(s) + 12

Cl2(g) NaCl(s) + 411 kL of energy

In other words, combination reactions are exothermic.

Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.For example: In the process of photosynthesis, plants use the energy from the sun to convert carbondioxide and water to glucose and oxygen.

6CO2(g) + 6H2O( ) Sunlight C6H12O6(aq) + 6)2(g

Glucose

Q.18 Why is respiration considerd an exothermic reaction ? Explain.

Ans. Energy is required to support life. Energy in our body is obtained from the food we eat. Duringdigestion, large molecules of food are broken down into simpler substances such as glucose. Glucosecombines with oxygen in the cells and provides energy. The special name of this combustion reaction isrespiration. Since energy is released in the whole process, it is an exothermic process.

C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O( ) + Energy

Glucose Oxygen Carbon dioxide Water

Q.19 Why are decomposition reactions called the opposite of combination reactions? Write equations forthese reactions.

Ans. Decomposition reactions are those in which a compound breaks down to form two or more substances.These reactions require a source of energy to proceed. Thus, they are the exact opposite of combina-tion reactions in which two or more substances combine to give a new substance with the release ofenergy.

Decomposition reaction: AB + Energy A + B

2H2O( ) Electrolysis 2H2(g) + O2(g)

Combination reaction: A + B AB + Energy

2H2(g) + O2(g) 2H2O( ) + Energy

Q.20 Write one equation each for decomposition reactions where energy is supplied in the form of heat, lightor electricity.

Ans. (a) Thermal decomposition:

2FeSO4(s) Fe2O3(g) + SO2(g) + SO3(g)

Ferrous sulphate Ferric oxide Sulphur dioxide Sulphur trioxide

(b) Decomposition by light:

2AgCl(s) Light 2Ag(s) + Cl2(s)

Silver chloride Silver Chlorine

(c) Decomposition by electricity:

2Al2O3(aq) Electricity 4Al(s) + 3O3(g)

Aluminium oxide Aluminium Oxygen



Q.21 What is the difference betuJeen dispiacemen[ and double displacement reactions? Write equations forthese reactions.

Ans. In a displacement reaction, a more reactive element replaces a less reactive element from acompound.

A + BX AX + B; where A is more reactive than B

In a double displacement reaction, two atoms or a group of atoms shift places to form new compounds.AB + CD AD + CB

For example:

Displacement reaction:

CuSO4(aq) + Zn(s) ZnSO4(aq) + Cu(s)

Double displacement reaction:

Na2SO4(aq) + BaCl2(aq) BaSO4(s) + 2NaCl(aq)

Q.22 In the refining of silver, the recovery of silver from silver nitrate solutior. involved displacement bycopper metal. Write down the reaction involved.

Ans. 2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag(s)

Silver nitrate Copper Copper nitrate Silver

Q.23 What do you mean by a precipitation reaction? Explain by giving examples.

Ans. A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.

For example:

Na2CO3(aq) + CaCl2(aq) CaCO3(s) + 2NaCl(aq)Sodium carbonate Calcium chloride Calcium carbonate Sodium chloride

In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.Another example of precipitation reaction is:Na2SO4(aq) + BaCl2(aq) BaSO4(s) + 2NaCl(aq)

Sodium sulphate Barium chloride Barium sulphate Sodium chloride

In this reaction, barium sulphate is obtained as a precipitate.

Q.24 Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation (b) ReductionAns. (a) Oxidation is the gain of oxygen.

For example:

(i) CO + H2 2 CO + H O2

Addition of oxygen-oxidation

(ii)2Cu + O2 2 uC O

Gain of oxygen - oxidation

In equation (i), H2 is oxidized to H2O and in equation (ii), Cu is oxidised to CuO.(b) Reduction is the loss of oxygen.

For example:

(i) CO + H2 2 CO + H O2

Removal of oxygen - reduction

(ii) CuO + H2 Cu + H O2

Loss of oxygen - reduction

in equation (i), CO2 is reduced to CO and in equation (ii), CuO is reduced ro Cu.



Q.25 A shiny brown-cloured element 'X' on heating in air becomes black in colour. Name the element 'X' and

the black coloured compound formed.

Ans. ‘X’ is copper (Cu) and the black-coloured ocmpound formed is copper oxide (CuO). The equation of the

reaction involved on heating copper is given below.

2Cu + O2Heat 2CuO

(Shiny brown in colour) (Black in colour)

Q.26 Why do we apply paint on iron articles?

Ans. Iron articles are painted because it prevents them from rusting. When painted, the contact of ironarticles from moisture and air is cut off. Hence, rusting is prevented. Their presence is essential for

rusting to take place.

Q.27 Oil and fat containing food items are flushed with nitrogen. Why?

Ans. Nitrogen is an inert gas and does not easily read with these substances. On the other hand, oxygen

reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed

with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack,

rancidity of oil and fat containing food items is avoided.

Q.28 Explain the following terms with one example each.

(a) Corrosion (b) Rancidity

Ans. (a) Corrosion: Corrosion is defined as a process where materials, usually metals, deteriorate as a

result of a chemical reaction with air, mOisture, chemicals, etc.

For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.

4Fe + 3O2 + nH2O 2Fe2O3.nH2O

Hydrated iron oxide

This hydrated iron oxide is rust.

(b)Rancidity: The process of oxidation of fats and oils that can be easily noticed by the change in

taste and smell is known as rancidity.

For example, the taste and smell of butter changes when kept for long.

Rancidity can be avoided by:

(1) Storing fooo in air tight containers

(2) Storing fooo in refrigerators

(3) Adding antioxidants

(4) Storing food in an environment of nitrogen



Type I- Very Short Answer QuestionsQ.1 Why does not a wall immediately acquire a white

colour when a coating of slaked lime is appliedon it? [C.B.S.E. 2010]

Q.2 What is ruet?

Q.3 What is the difference b/w the following 2

reactions? [C.B.S.E. 2011](a) Mg + 2HCl MgCl2 + H2

(b) NaOH + HCl NaCl + H2O

Q.4 Suggest 2 ways to check the rancidity of foodarticles. [C.B.S.E. 2011, 2012]

Q.5 What is the role of oxidising agent in a reaction? [C.B.S.E. 2010]

Q.6 What is meant by a skeletal chemical equation? [C.B.S.E. 2010]

Q.7 On what basis is a chemical equation balanced? [C.B.S.E. 2010]

Q.8 Balance following chemical equation:-

Pb(NO3)2(s) Heat Pbo(s) + NO2(g) + O2(g)

[C.B.S.E. 2009]

Q.9 Write a balanced chemical equation torepresent the following equation:- Iron reactswith stream to form Iron (II, III) oxide andHydrogen gas.[C.B.S.E. Sample paper 2011]

Q.10 Balance the following chemical equation.(i) FeCl2 + H2S HCl + Fes(ii) HNO3 + Ca(OH)2 Ca(NO3)2 + H2O

[C.B.S.E. 2008]

Q.11 What happens chemically when Quick lime isadded to water? [C.B.S.E. 2010]

Q.12 Give one example of each exothermic reaction

and endothermic reaction? [C.B.S.E. 2010]

Q.13 What is the brown coloured gas evolved when

lead nitrate crystals are heated in a dry testtube? [C.B.S.E. 2010]

Q.14 In the reaction MnO2 + 4HCl MnCl2 + 2H2O+ Cl2. Identify which one is reduced and whichone is oxidized? [C.B.S.E. 2010]

Q.15 Complete the equation:- [C.B.S.E. 2010]

Fe2O3 + 2Al

Q.16 Take a small amount of calcium oxide or quicklime in a beaker and slowly add water to this.Is there any change in temperature?

[C.B.S.E. 2010, 2011]

Q.17 Which chemical process is used for obtaininga metal from its oxide? [C.B.S.E. 2010]

Type II - Short Answer Type Questions

Q.18 Write balance chemical equation “duringrespiration combustion of glucose takes placeproducing carbon dioxide water and energy”.

Q.19 A zinc rod is left for nearly 20 minutes in acopper sulphate solution. What change wouldyou observe in zinc rod?

Q.20 Name a reducing agent that can be used toobtain manganese from manganese dioxide.Write balanced chemical equation for thereaction? [C.B.S.E. Delhi 2009]

Q.21 Give reason, silver articles become black aftersometime when exposed to air?

[C.B.S.E. 2008]

Q.22 What is the role of catalyest in a chemicalreaction? [C.B.S.E. 2007]

Q.23 Name 2 salts which are used in black and white

photography? [C.B.S.E. 2010, 11]

Q.24 State the essential requriement for rusting?

[C.B.S.E. 2013]

BOARD PROBLEMSEXERCISE – I



Type III- Long Answer Type Questions

Q.25 When a water insoluble substance “X” is addedto dil. Hydrochloric acid, a colourless, odourlessgas is evolved. When the gas is passed throughlime water, it turns milky. Write the formula

of gas evolved and balanced chemical equationof the reaction.

Q.26 (a) Write one equation each for decompositionreaction when energy is supplied in the form

of (i) Heat (ii) Light.

(b) Account for following:-

(i) Paint is applied on Iron articles.

(ii) Oil and fat containing food items are flushedwith nitrogen. [C.B.S.E. 2011]

Q.27 A green coloured hydrated salt of Iron losesits water of crystallisation and smell of burning

sulphur is given. Identify the salt and writechemical equation. [C.B.S.E. 2011]

Q.28 (a) Why cannot a chemical change be normallyreversed?

(b) Why is it always essential to balance a

chemical equation?

(c) Why do diamond and graphite, 2 forms ofcarbon evolve different amounts heat oncombustion?

(d) Why does milkness disappear when CO2

is passed throug lime water in excess?

(e) Can rusting of Iron take place in distilledwater?

Q.29 X + YSO4 XSO4 + Y

Y + XSO4 No reaction

and of the 2 elements “X” and “Y” which ismore reactive and why? [C.B.S.E. 2011]

Q.30 (a) Can a combination reaction be an oxidationreaction? [C.B.S.E. 2011]

(b) How will you test whether the gas evolvedin a reaction is hydrogen?

(c) Why does copper not evolve hydrogen onreacting with dilute sulphuric acid?

Q.31 A brown substance “X” on heating in air forms

a substance “Y”. When hydrogen gas is passed

over heated “Y”. It again changes back into

“X”. [C.B.S.E. 2010]

(i) Name the substance X and Y.

(ii) Name the chemical processes occuring

during both changes.

(iii) Write chemical equations?

Q.32 Explain why:- [C.B.S.E. 2011]

(i) Respiration is an Exothermic reaction.

(ii) When blue salt of CuSO4 is heated it

becomes colourless?

Q.33 In electrolysis of water [C.B.S.E. 2012]

(i) Name the gas collected at the cathod and

anode respectively.

(ii) Why is the volume of one gas collected

at one electrode double that at the other?

Name this gas?

(iii) How will you test the evolved gases?

Q.34 Identify the type of reaction[C.B.S.E. 2012]

(i) CuSO4 + Zn ZnSO4 + Cu

(ii) BaCl2 + ZnSO4 BaSO4 + ZnCl2

(iii) NH4Cl Heat NH3 + HCl

(iv) HgCl2 + SnCl2 HgCl2 + SnCl4(v) 2KClO3 Al2O4 + 2Fe

(vi) 2All + Fe2O3 Al2O3 + 2Fe

Q.35 Balance the following equation [C.B.S.E. 2008]

(i) H2SO4(aq.) + NaOH(aq.) Na2SO4(aq.) + H2O (l)

(ii) KCN(aq.) + H2SO4(aq.) K2SO4(aq.) + HCN(g)

(iii) HgCl2 + SnCl2 Hg2Cl2 + SnCl4

(iv) Al2O3 + H2SO4 Al2(SO4)3 + H2SO4

(v) Al2(SO4)3 + NaOH Al(OH)3 + Na2SO4



Q.36 Identify the type of reaction

(i) 2H2O Electrolysis 2H2 + O2

(ii) 2NH3 + H2SO4 (NH4)2SO4

(iii) AgNO3 + Nacl NaNO3 + Agcl

(iv) Zn(s) + 2AgNO3 (aq.) Zn(NO3)2(aq.) + 2Ag(s)

(v) Ni(NO3)2(aq.) + 2NaOH(aq.) Ni(OH)2

+ 2NaNO3(aq.)

(vi) MgO(s) + C(s) CO(g) + Mg(s)

Type IV- Thinking Based/Skill Based Questions

Q.37 The marble statues slowly get carroded whenkept in open for a long time. Give suitableexplanation?

Q.38 (a) Based on reactions given below, arrangethe metals invloved in these reactions indecreasing order of reactivity. Give suitableexplanation.

(i) Zn + CuSO4 ZnSO4 + Cu

(ii) Cu + 2AgNO3 Cu (NO3)2 + 2Ag

(i) Zn + FeSO4 ZnSO4 + Fe

(ii) FE + CuSO4 FeSO4 + Cu

(b) What is the nature of reactions?

Q.39 A, B and C are 3 elements which undergochemical reactions according to following

equations:-

A2O3 + 2B B2O3 + 2A

3CSO4 + 2B B2(SO4)3 + 3C

3CO + 2A A2O3 + 3C

Ans. Following Questions

(a) Which element is more reactive?

(b) Which element is least reactive?

Q.40 You are given following materials:-

(i) Marble chips (ii) Dil. HCl acid (iii) zinc granules

Identify type of reaction when marble chipsand zinc granules are added separately to acidtaken in two tubes. Write chemical equation

in each case.

Q.41 2gm of FeSO4 Crystals were heated in a hardglass test tube and observations recorded.

(a) What was the successive colour change?

(b) Identify liquid droplets collected on cooler

part of test tube.

(c) What type of odour is observed on heatingFeSO4 Crystals?



Q.1 The example of a physical change is

(A) milk is left at room temperature in summers

(B) an Iron is heated

(C) Iron tawa is left emposed to humid air

(D) Food is cooked

Q.2 Which of the following is/are exothermicprocesses

(i) Sublimation of NH4Cl

(ii) Quick lime is added to water

(iii) Evaporation of water

(iv) Dilution of an acid

(A) (i) and (ii) (B) (ii) and (iii)

(C) (iii) and (iv) (D) (ii) and (iv)

Q.3 Fe2O3 + 2Al Al2O3 + 2Fe, is a

(i) combination rxn

(ii) Displacement Rxn

(iii) redox Rxn

(iv) Double displacement Rxn

(A) (i) and (ii) (B) (ii) and (iii)

(C) (iii) and (iv) (D) (ii) and (iv)

Q.4 Silver Bromide, On expourse to sunlight turnsgrey due to

(A) Formation of silver by its decomposition

(B) Oxidation of silver Bromide

(C) Sublimation of silver Bromide

(D) Decomposition of bromine gas from silverbromide

Q.5 Water on electrolysis decomposes to hydrogenand oxygen. the mole ratio of H2 and O2 is

(A) 1 : 2 (B) 1 : 1

(C) 2 : 1 (D) 4 : 1

Q.6 Which of the following gases used for storageof fresh sample of an oil for a long time

(A) Nitrogen and Oxygen

(B) CO2 and Helium

(C) CO2 and oxygen

(d) Nitrogen and Helium

Q.7 50 ml of water was taken in a beaker A, Band C. A small amount of CuSO4, NaOH andNaCl were added to beaker A, B and Crespectively. The temperature of beaker A andB increased where in beaker c decreases. Thecorrect statement (s) is/are(i) In beaker “C” exothermic process has

occurred.(ii) In beaker “A” and “B” exothermic process

has occurred.(iii) In beaker A and B endothermic process

has occurred.(iv) In beaker “C” endothermic process has

occured.(A) (i) and (ii) (B) (ii) and (iii)(C) (iii) and (iv) (D) (ii) and (iv)

Q.8 Example of a chemical change is(A) fermentation of rice(B) breathing(C) curdling of milk(d) all of above

Q.9 Which of the following is a double displacementreaction?(A) 2H2 + O2 2H2O(B) FeSO4 + Zn ZnSO4 + Fe(C) CH4 + 2O2 2H2O + CO2(D) Na2SO4 + Bacl2 BaSO4 + 2Nacl

Q.10 Which of the following is not a decompositionreacion?(A) CaCO3 CaO + CO2(B) 2KClO3 2KCl + 3O2(C) Digestion of food in the body(D) H2 + Cl2 2HCl

Q.11 Which of the following represent a doubledisplacement reaction?(A) 2H2 + O2 2H2O(B) 2Mg + O2 2MgO(C) AgNO3 + NaCl AgCl + NaNO3

(D) H2 + Cl2 2HCl

Q.12 Which of the following is a displacementreaction?(A) CaCO3 CaO + CO2(B) CaO + 2HCl CaCl2 + H2O(C) Fe + CuSO4 FeSO4 + Cu(D) NaOH + HCl NaCl + H2O

OLYMPIAD QUESTIONSEXERCISE – II



Q.13 The reaction H2 + Cl2 2HCl is a –

(A) Decomposition reaction

(B) Combination reaction

(C) Double displacement reaction

(D) Displacement reaction

Q.14 Which of the following is a decompositionreaction?

(A) NaOH + HCl NaCl + H2O

(B) NH4CNO H2NCONH2

(C) 2KClO3 2KCl + 3O2

(D) H2 + I2 2HI

Q.15 Which of the following statement is incorrect?

(A) In oxidation, oxygen in added to a substance.

(B) In reduction, Hydrogen is added to asubstance.

(C) Oxidizing agent in oxidized.

(D) Reducing agent is oxidized.

Q.16 Which of the following is a combustion reaction–

(A) Boiling of water

(B) Melting of wax

(C) Burning of petrol

(D) None of these

Q.17 Which of the following is a redox reaction?

(A) CaCO3 CaO + CO2

(B) H2 + Cl2 2HCl

(C) CaO + 2HCl CaCl2 + H2O

(D) NaOH + HCl NaCl + H2O

Q.18 Which statement is correct about the followingreaction?

ZnO + CO Zn + CO2

(A) ZnO is being oxidized

(B) CO is being reduced

(C) CO2 is being oxidized

(D) ZnO is being reduced

Q.19 The reaction C + O2 CO2 + Heat is a –

(A) Combination reaction

(B) Oxidation reaction

(C) Exothermic reaction

(D) All of the above

Q.20 Conversion of CaCO3 in to CaO as per followingreaction is an example of –

CaCO3 CaO + CO2(A) Decomposition reaction(B) Reduction reaction(C) Oxidation reaction(D) None of these

Q.21 Fe2O3 + 2Al Al2O3 + 2Fe This reactionis an example of –

(A) Combination reaction

(B) Double displacement reaction

(C) Decomposition reaction

(D) Displacement reaction

Q.22 In reaction SO2 + 2H2S 2H2O + 3S thereducing agent is –

(A) SO2 (B) H2S

(C) H2O (D) S

Q.23 What happens when dil hydrochloric acid isadded to iron fillings?

(A) Hydrogen gas and Iron chloride areproduced.

(B) Chlorine gas and Iron hydroxide areproduced.

(C) NO reaction takes place

(D) Iron salt and water are produced.

Q.24 When Iron nails are added to an aquous solutionof copper sulphate, a chemical change occurs,which of the following is not true about thisreaction?

(A) Blue colour of the solution fades.(B) Iron nails becomes brownish in colour.

(C) It is a displacement reaction.

(D) Iron nails dissolves completly.

Q.25 Potassium reacts with bromine to formpotassium bromide. [NTSE]

(A) 2K + Br 2KBr

(B) K2 + Br2 2 KBr

(C) K2 + Br2 KBr2(D) K2 +Br2 KBr



Q.26 A silver spoon on exposure to air reacts withthe sulphur present in air to give a black materialcalled ______. [NTSE]

(A) Silver oxide (B) Silversulphide

(C) Tarnish (D) Coal tar

Q.27 In the decomposition of sulphates by heat,which is the gas formed exclusively along withthe metal oxide? [NTSE]

(A) SO2 (B) SO3

(C) SO3 and SO2 (D) H2SO3

Q.28 Which among the following is not a physicalchange? [NTSE]

(A) Melting of solids to liquids

(B) Vapourisation of liquids to gases

(C) Liquefaction of gases to liquids

(D) Decay of matter

Q.29 Which among the following reactions areexothermic in nature? [NTSE]

(A) Bond formation

(B) Bond breaking

(C) Combustion of carbon

(D) Both (A) and (C)

Q.30 The reaction P4 + 3O2 2P2O3 is ____.

(A) synthesis reaction [NTSE]

(B) displacement reaction

(C) decomposition reaction

(D) combustion

Q.31 PbO2 + 4HCl PbCl2 + 2H2O + Cl2. Thesubstance undergoing oxidation is _____.

[NTSE]

(A) lead dioxide (B) hydrochloric acid

(C) hydrogen (D) lead chloride

Q.32 In the equation FeCl3 + xNaOH yNaCl +Fe(OH)3, the value of x and y, respectively,are _____. [NTSE](A) 3 and 1 (B) 3 and 3

(C) 2 and 3 (D) 3 and 4

Q.33 The rate of a chemical reaction is altered by______. [NTSE](A) nature of reactants(B) changing temperature(C) using a catalyst(D) all the above

Q.34 Which of the following is an example of areversible reaction? [NTSE]

(A) 3Fe + 4H2O 1237 K Fe3O4 + 4H2

(B) CaCO3 CaO + CO2(C) AgNO3 + KCl AgCl + KNO3(D) NaOH + HCl NaCl + H2O

Q.35 Which of the following reaction will not takeplace? [NTSE](A) Zn + FeSO4 ZnSO4 + Fe(B) 2Kl + Cl2 2KCl + I2(C) Zn + MgSO4 ZnSO4 + Mg(D) Mg + CuSO4 MgSO4 + Cu

Q.36 When hydrogen sulphide gas is passed througha blue solution of copper sulphate, a blackprecipitate of copper sulphide is obtained andthe sulphuric acid so formed remains in thesolution. The reaction is an example of(A) a combination reaction [NTSE](B) a displacement reaction(C) a decomposition reaction(D) a double decomposition reaction

Q.37 In the following equationsNa2CO3 + xHCl 2NaCl + CO2 + H2O thevalue of x is: [NTSE](A) 1 (B) 2(C) 3 (D) 4

Q.38 Combustion of fuel is [NTSE](A) displacement reaction(B) double displacement reaction(C) oxidation reaction(D) isomerisation reaction

Q.39 The reaction between acid and base to formsalt and water is an example of [NTSE]

(A) decomposition reaction(B) combination reaction

(C) displacement reaction

(D) double displacement



Q.40 Which of the following reactions are exothermicin nature? [NTSE]

(A) Combustion of Carbon

(B) Bond breaking

(C) Bond formation

(D) Both (A) and (C)

Q.41 Which of the following changes is not a physicalchange? [NTSE]

(A) glowing of filament in bulb

(B) combustion

(C) boiling of water

(D) sublimation

Q.42 The substance that looses electrons is calledas: [NTSE]

(A) oxidizing agent (B) reducing agent

(C) catalyst (D) none of above

Q.43 The process of reduction involves [NTSE]

(A) removal of hydrogen

(B) gain of electrons

(C) addition of oxygen

(D) loss of electrons

Q.44 In the reaction H2S + Cl2 2HCl + S, theoxidizing agent is: [NTSE]

(A) H2S (B) Cl2(C) HCl (D) S

Q.45 Select Redox reaction from the following

(A) Zn + CuSO4 ZnSO4 + Cu [NTSE](B) CaO + 2HCl CaCl2 + H2O

(C) NaOH + 2HCl NaCl2 + H2O(D) CaCO3 CaO + CO2

Q.46 Which of the following reactins is not correct?

[NTSE]

(A) 2AgNO3 + Cu Cu(NO3)2 + 2Ag(B) Cl2 + 2KI 2KCl + I2(C) FeSO4 + Cu CuSO4 + Fe

(D) CuSO4 + Zn ZnSO4 + Cu

Q.47 Consider the reactions [NTSE]

CuSO4 + Fe FeSO4 + Cu

FeSO4 + Zn ZnSO4 + Fe

(A) Zn is most reactive, Fe is least reactive(B) Fe is most reactive and cu is least reactive

(C) Zn is most reactive and cu is least reactive(D) Cu is most reactions, Fe is least reactive

Q.48 Choose the incorrect statement. [NTSE]

(A) physical change is reversible

(B) physical change results information of newsubstances

(C) chemical change is permanent

(D) physical change is accompanied by energychange

Q.49 Which of following is fast reaction? [NTSE]

(A) reaction between H2 and O2 to form H2O(B) reaction between acid and base to formsalt and water

(C) hydrolysis of ester

(D) hydrolysis of sugar to glucose

1. C 2. D 3. B 4. A

5. C 6. D 7. D 8. D

9. D 10. D 11. C 12. C

13. C 14. C 15. C 16. C

17. B 18. D 19. D 20. A

21. D 22. B 23. A 24. D

25. A 26. B 27. B 28. D

29. D 30. D 31. B 32. B

33. D 34. A 35. C 36. D

37. B 38. C 39. D 40. D

41. B 42. B 43. B 44. B

45. A 46. C 47. C 48. B

49. B

ANSWER KEY

NUTRITIONPage # 78


NUTRITIONIt is the method of obtaining nutrients from the environment. It can be defined as the process bywhich the organism ingests, digests, absorbs, transports and utilises nutrients and disposes off theirend products.

NUTRIENTThe different component of food that have distinct functions like providing energy. materials for bodybuilding, maintenance & regulation of metabolism are called nutrient.For exmple-Proteins, Minerals, Vitamin, Carbohydrates, fats.

MODES OF NUTRITIONMode of nutrition

Autotrophic nutrition Heterotrophic nutrition

Holozoicnutrition

Saprotrophicnutrition

Pasrsiticnutrition

(a) Autotrophic NutritionIn this type of nutrition, organisms synthesise the organic materials they require from inorganic sources.All green plants are autotrophic and use light as a source of energy for the synthesis.

AutotrophsThe organisms which make their own food from carbon dioxide and water in the presence of sunlightand chlorophyll are called autotrophs. These organisms are also called producers and include greenplants and some bacteria.

PHOTOSYNTHESISIt is the process by which green parts of the plant synthesise organic food in the form of carbohydratesfrom CO2 and water in the presence of sunlight.

6CO2 + 6H2O lchlorophyl

light C6H12O6 + 6O2

In plants and most algae it occurs in the chloroplasts and there are two principal reactions:(i) Light reaction (light-dependent) requires the presence of light energy from sunlight which is obtainedby photosynthetic pigments, i.e., chlorophyll and used to bring about the photolysis of water.

H2O 2H+ + 2e-

(ii) Dark reaction (light-independent) i.e., this reaction is not dependent on light and during thisreaction carbon dioxide is reduced to carbohydrate in a metabolic pathway known as the Calvin cycle.

1. NUTRITION

The whole process by which an organismobtains its food is referred to as nutrition.

NUTRITION Page # 79


Difference between light and dark reactions

Features Light reaction Dark reactionRequirement of light Required Not required

Takes place inside Grana part of the chloroplastThe stroma region of chloroplast

ATP and NADPH2

ATP and NADPH2 are producedby the conversion of light energyinto chemical energy

ATP and NADPH2 formedduring light reaction areused for the fixation ofCO2 into carbohydrate

Sugar formation No sugar formation takes placeSugar formation takesplace

Release of oxygen Oxygen is released No oxygen is released

VARIOUS COMPONENTS OF PHOTOSYNTHESISVarious components necessary for the process of photosynthesis are :1.Chlorophyll2. Carbon dioxide3. Sunlight4. WaterThis can be demonstrated with the help of various experiments.

1. ChlorophyllChlorophyll is green pigment present in the green leaves.

Activity-1.1SCIENCE COMES ALIVETo prove that chlorophyll is essential for photosynthesis.

ApparatusPlant with variegated leaves, Apparatus for starch test i.e., iodine solution, beaker, test tubes.

NON-GREEN

GREEN(CHLOROPHYLL)

BLUE BLACK(STARCH)

COLOURLESS(NO STARCH)

Fig. 1 Apparatus to show that chlorophyll is essential for phtosynthesis

Procedure

1. A potted plant with variegated leaf (Coleus, Croton) is kept in darkness for two days to make theleaves starch-free.

2. A plant is then kept in sunlight for few hours.3. A leaf is removed from the plant and tested with iodine for starch, after decolourising it first with

water and then alcohol.

ConclusionIt is seen that the portions of leaves which are devoid of chlorophyll remain colourless (starch free)whereas the rest of the leaf turns blue-black due to the presence of starch.

PRACTICE ZONE 1.1

1. Why do plants need magnesium ?2. What type of the plants do we use in the experiment to prove that chlorophyll is necessary for

photosynthesis.3. What substance does a plant need to be able to convert glucose into proteins ?

NUTRITIONPage # 80


2. Carbon-Dioxide

Photosynthesis has been found to takes place in a very wide range of CO2 concentration.Within the range the rate of photosynthesis will decrease or increase with decrease or increase inCO2 concentration, provided other factors are not limiting.Relatively high concentration of CO2, reduces the rate of photosynthesis and if given for aconsiderable period of time, has detrimental effect on the process itself.

Activity-1.2SCIENCE COMES ALIVETo prove that carbon dioxide is necessary for the process of photosynthesis.

Apparatus

Two healthy potted plants, Potassium hydroxide (KOH), 2 bell jars, watch-glass, vaseline, 2 glassplates, Iodine solution, H2O and alcohol.

Procedure1. Take two healthy potted plants of same size.2. Destarch them by keeping in a dark room for 3-4 days.3. Now place these potted plants on separate glass sheets.4. Place watch glass containing KOH by the side of one of the plants. KOH has the property to absorb

carbon dioxide.5. Now cover these potted plants with bell jars.6. To make the apparatus air tight use vaseline to seal the botton of the jars to glass plates.7. Keep this experimental setup in sunlight for 3 to 4 hours.8. Pluck one leaf from each plant.

POTTED PLANT

GLASS SHEET

NO WATCH-GLASSCONTAINING KOH

BELL JAR

WATCH-GLASSCONTAINING

KOHA B

BELL JAR

Fig. 2 Apparatus to show that CO2 is necessary for the process of photosynthesis

9. Perform starch test for both the leaves by decolourizing leaf first in water, then in alcohol andfinally testing with iodine solution.

10. Leaf which was within bell jar with KOH solution gives a negative test whereas other one givespositive test.

ConclusionThe experiment clearly proves the fact that carbon dioxide is absolutely essential for photosynthesis.The part of the leaf which could not show iodine test positive or manufacture starch had all therequirements for photosynthesis except CO2, which was absorbed by KOH in the bottle.

ONYOURTIPS

The light intensity where in the photosynthesising organs neither takes

CO nor release the same is calledcompensation point.

2

NUTRITION Page # 81


3. Sunlight

Activity-1.3SCIENCE COMES ALIVETo prove that light is necessary for photosynthesis-Starch Printing Test.

ApparatusGanong's light screen or two strips of black paper. A destarched plant, Apparatus for starch test.

Procedure1. Take a Ganong's light screen. It has a small metallic box with ventilating holes. To the is attached

a spring handle, bearing a lid at its one end which fits over the metallic box lightly.The lid has a design within its centre. You can even use two black paper strips to cover the leaf.

2. A potted plant is kept in the dark for two days to make the leaves starch free.3. A leaf is partly covered with a piece of black paper or by a Ganong's light screen.4. The pot is then kept in the sunlight for few hours.5. The leaf is then tested with jodine solution for starch.

ConclusionIt is seen that the starch is formed only in the exposed portion of the leaf whereas covered portionremains starch-free because light was not available to such patches for photosynthesis.

STARCH FORMED

BLACK PAPERNO STARCHFORMATION

Fig. 3 Apparation to show that light is required for phtosythsis

PRACTICE ZONE 1.1

1. Plants need magnesium to make chlorophyll.2. Desarched potted plants with variegated leaves eg. Croton and Pothos.3. Nitrogen.

4. Water

Plants absorb water from the soil with the help of root system. The effect of water deficiency onthe rate of photosynthesis is indirect one.Decrease in H2O content of the leaves may cause partial or complete closure of stomatal opening,and hence a reduction in the rate of diffusion of CO2.A partial drying of the cell walls cause decrease in its permeability to CO2, Another indirect effect ofwater deficiency is that the accumulation of sugar within the cells increases the rate of respirationand thus decreases apparent photosynthesis

(b) Heterotrophic Nutrition

The type of nutrition in which organisms derive their food (nutrients) from other living organisms. Inheterotrophic nutrition, the energy is derived from the intake and digestion of the organic substances,normally of plant or animal tissue. Heterotrophic mode of nutrition are of different types :(i) Saprotrophic NutritionIt refers to the mode of nutrition in which organisms obtain nutrients from the dead and decayingorganic matter, e.g., fungi, yeast and bacteria are called saprophytes.(ii) Parasitic NutritionIt refers to the mode of obtaining food synthesised by others. The organism which obtains food iscalled the ‘parasite’ and the organism from which food is absorbed is called the ‘host’. This nutrition isobserved in fungi, bacteria, a few plants like Cuscata and some animals like Plasmodium and roundworm.(iii) Holozoic NutritionIt refers to the mode of nutrition in which the complex organic matter in the form of solid food isingested, digested and then absorbed into the cells and utilised, e.g. amoeba, frog, human beings.

HeterotrophsThe organisms which cannot make their food and depend directly or indirectly on autotrophs for theirsurvival are called heterotrophs. These organisms include animals and fungi.

NUTRITIONPage # 82


TYPE OF HETEROTROPHIC NUTRITION

1. Saprophytic or Saprotrophic Nutrition :It is a mode of heterotrophic nutrition in which food is obtained from organic remains like deadorganisms, excreta, fallen leaves, broken twigs, food articles, etc. Organisms performing saprophyticnutrition are called saprophytes.

2. Parasitic Nutrition : · It is a mode of hetrotrophic nutrition in which a living organisms flourishes by obtaining food from

another living organism. The lving organisms which obtains food and shelter from another organism iscalled parasite. The organism which provides food and shelter to a parasite is known as host. Anexternal plant parasite is Cuscuta (Amarbel). It is a non-green plant that sends haustroria or suckingroots into host plant for obtaining food and water.

3. Holozoic Nutrition :

It is a mode of heterotrophic nutrition which involves intake of solid pieces of food. Since solid food istaken in, holozoic nutrition is also called ingestive nutrition. The food may consist of another animal,plant or its parts. Depending upon the source of food, holozoic organisms are of three types –Herbivores, carnivores, omnivores.

Herbivores :

(L.herba-plant, vorare-to eat)

They are holozoic organisms which feed on plants or plant parts, e.g., Cow, Buffalo, Deer, Goat, Rabbit,Grasshopper, Elephant, Squirrel, Hippopotamus.

Carnivores :

They are animals which feed on other animals. Carnivores are also called predators they hunt, kill andfeed on their preys, e.g. Lion, Tiger, Leopard, Snake, Hawk.

Omnivores :

(L.omnis-all, vorare-to eat)

They are holozoic organisms which feed on both plant and animal materials, e.g. Cockroach, Ant, Pig,Crow, Rat, Bear, Dog, Humans.

NUTRITION IN AMOEBA

Protozoan protests carry out holozoic nutrition through intracellular digestion.

Fig. - 4 Nutrition in Amoeba

ONYOURTIPS

Free-living platyhelminthes (e.g., planaria) possess bothkinds of digestion. Humanshave extracellular digestion.

NUTRITION Page # 83


Some protests can ingest food particle from any point on the surface (e.g., Amoeba) while others havefixed points for the same (e.g., Paramoecium). Protozoans like Amoeba capture food with the help oftemporary finger-like processes called pseudopodia. Protozoans like (Paramoecium have small hair-likeprocesses called cilia.) Beating of cilia creates current in water that pushes food particle throughcytostome or cell mouth. The process of ingestion of solid food particle by a cell or unicellular organismis called phagocytosis.

As soon as Amoeba comes in contact with a food particle or prey, it throws pseudopodia all around thesame. The tips of encircling pseudopodia fuse and the prey comes to lie in a vesicle or phagosome. Thismethod of intake of food is called circumvallation. Amoeba can also ingest food by other methods likeimport, circumfluence and invagination.

DIGESTIVE SYSTEM OF HUMAN

The organs which are responsible for ingestion, digestion, absorption, assimilation and egestion constitutethe digestive system. The digestive system comprises of the alimentary canal and associated digestiveglands.

Digestive system

Alimentary canal Digestive Glands

Mouth Buccalcavity

Oesophagus Stomach Intestine

Small Intestine Large Intestine

Duodenum Jejunum lluemCaecum

ColonRectum

(A) Alimentary canal

The alimentary canal is basically a long tube extending from the mouth to the anus.

It is differentiated into following parts.

(i) Mouth

It is a transverse slit bounded by movable lips. The lips serve to close and open mouth. holding thefood in between and also help in speaking.

The floor of the buccal cavity has a tongue bearing taste buds. Man possess teeth on both the jaws.There are 32 teeth of four different types, namely incisors, canines, premolars and molars.

Digestion may be intracellular (Paramoecium) or extracellular (multicellular animals).

The process of digestion starts in the mouth cavity and continues upto the intestine.

In the mouth, food gets mixed up with saliva secreted by salivary glands.

Saliva contains an enzyme ptyalin which breaks polysaccharide starch into disaccharide maltose.

Maltose Starchamylase)Salivary (

Ptyalin

The food from the mouth cavity passes into the stomach through the oesophagus.

ONYOUR

TIPS

Apart from the presence of food,the sight, smell or even touch ofone's favourite food can initiate

secretion of gastric juices.

NUTRITIONPage # 84


(ii) Pharynx

It is a short, conical region that lies after the mouth cavity. The pharynx are divided into two parts —the nasopharynx which lies behind the nasal cavities and the oropharynx which lies behind the mouth.

(iii) Oesophagus (food pipe)

It is a long, narrow, muscular tube which leads to the stomach, The oesophagus is a collapsible musculartube leading from pharynx to stomach. There are no digestive glands but mucus glands are present.

(iv) Stomach

It is a thick, muscular and J shaped sac present on the left side of upper part of abdomen. Gastricglands are present in the wall of stomach. These releases gestric juice or digestive juice, whichcontains mucus. hydrochloric acid and a protein digesting enzyme called pepsin.

Mucus lubricated the food and protects the inner linning of the stomach from the action of HCl.

HCl creates an acidic medium, which facilitates the action of enzyme pepsin and kills the bacteriapresent in food.

Pepsin breaks down proteins into peptides.

Sphincter muscles regulate the exit of food from stomach into intestine due to peristaltic waves ofstomach.

Fig. -5 Human alimentary canal(v) Intestine

It is the largest part of alimentary canal which is fitted into a compact space because of extensivecoiling. It is distingushed into small intestine and large intestine.

Small intestine

The small intestine is the site of the complete digestion of carbohydrates. proteins and fats.It receives the secretions of the liver and pancrease for digestion.

Food is mixed with three digestive juices (bile juice, pancreatic juice and intestinal juice)

Bile juice (from the liver) provide alkaline medium and emulsifies fats (conversion of larger fat globulesinto smaller fat droplets) but it is non enzymatic digestive juice so has no chemical action on food.

Pancreatic juice (from the pancreas) contains trypsin, pancreatic amylase and pancreatic lipaseenzymes which digest the peptons, starch and fats into peptides, maltose and fatty acids and glycerolrespectively.

The wall of intestine secretes intestinal juice which contains enzymes for complete digestion of proteinsinto amino acids, carbohydrates into glucose and fat into fatty acid and glycerol.

The inner lining of the small intestine has numerous finger like projections called villi which increase thesurface area for absorbtion of digested food.

These are richly supplied with blood vesseles.

NUTRITION Page # 85


Large Intestine

It is much shorter and wider than small intestine and is differentiated into three regions viz., caecum,which is small rounded blind sac from which vermiform appendix arises; colon is the inverted U-shapedtube and the rectum opens to exterior through anus.

(vi) Anus

The rest of the material is removed from the body via anus. The exit of waste material is regulated byanal sphincter.

(B) Digestive Glands

Various glands associated with alimentary canal are :

Fig. -6 Salivary glands of man

ONYOURTIPS

On eating food of our interest, wateringstarts in our mouth. This water is basically the saliva which is secretedby salivary glands that get activatedby eating and even seeing or thinking of good food.

(i) Salivary Glands

The salivary glands secrete the first of the digestive juices, the saliva. There are three pairs of salivary

glands, namely the parotids, sub-maxillary and sublingual glands.

(ii) Gastric Glands

They are branched tubular glands which lie in the mucus membranes of the stomach. They secrete

gastric juice, which is clear, acidic containing HCl, enzymes and mucus.

(iii) Liver

It is the largest gland in man and lies below diaphragm in the right upper part of abdomen. Liver comprises

of two lobes, right and left, where the right lobe is much larger than the left lobe. The cells of liver, i.e.,

hepatic cells produce bile juice which flows out of liver through hepatic ducts forming common bile duct

and opens into duodenum. Bile juice then flows into gall bladder through the cystic ducts.

NUTRITIONPage # 86


Fig. -7 Liver and Pancreas and their ducts(iv) PancreasIt is a soft lobulated gland present in between the loops of duodenum. It secretes pancreatic juicecontaining enzymes which is poured into duodenum with the help of pancreatic duct.

Table: Summary of the digestive enzymes of various glands with their secretions and end products ofDigestion in Man

Secretion

ONYOURTIPS

It is the tooth decay which involves destruction of the enamel layer of thetooth by acids produced by the actionof bacteria on sugar. If dental caries isnot treated, it can spread to the dentineand pulp of the tooth, causing inflammationa nd i n fe c t io n o f t h e to o th .

NUTRITION Page # 87


N.C.E.R.T TEXT BOOK SOLUTIONQ.1 Why is diffusion insufficient to meet the oxygen requirement of multicellular organisms like humans?

Ans. In humans, the body organisation is multicellular and complex. The living cells are not in direct constantwith environment because they are generally covered by dead cells. Air containing intracellular spacesare also absent so quick diffusion cannot occur. Cell to cell diffusion is very slow process and if it takesplace in humans then passage of oxygen in whole body will take about years. Thus, diffusion isinsufficient to deliver oxygen to all parts of a multicellular organisms like humans.

Q.2 What criteria do we use to decide whether something is alive?

Ans. The main criterion that is used to decide whether something is alive, is movement. Movements may beof different types like locomotion (running, walking), moving body parts, breathing movements, growthmovements and movement of molecules in various metabolic reactions. Besides movements, otherqualities found in living beings are self-built body organisation, presence of protoplasm, self repair,various vital life processes like metabolism, growth, nutrition, respiration, excretion and reproduction.

All living organisms have a definite lifespan and particular life cycle.

Q.3 What processes would you consider essential for maintaining life?

Ans. The processes essential for maintaining life are nutrition, metabolism, respiration, circulation/transpor-tation and excretion.

Q.4 What are the differences between autotrophic nutrition and heterotrophic nutrition?

Ans. In autotrophic mode of nutrition, organisms (green plants, some protists and bacteria) prepare theirown food from inorganic raw materials with the help of energy obtained from sunlight whereas inheterotrophic mode of nutrition, organisms obtain food prepared by autotrophs or from other organicsources as they cannot synthesise their own food. Heterotrophic nutrition may be saprophytic,parasitic and holozoic.

Q.5 Where do plants get each of the raw materials required for photosynthesis?

Ans. The raw materials required for photosynthesis are carbon dioxide and water. Plants obtain water fromthe soil through roots and carbon dioxide from the atmosphere through stomata present on leaves.

Q.6 What is the role of the acid in our stomach?

Ans. Hydrochloric acid (HCl) is secreted inside the stomach. The main functions of HCl are to

(i) stop the action of salivary amylase

(ii) kill the microbes present in the food

(iii) provide acidic medium necessary for the activation of the enzyme pepsin

(iv) make food soft

(v) convert pepsinogen and prorennin into active forms of pepsin and rennin.

Q.7 What is the function of digestive enzymes?

Ans. Digestive enzymes are hydrolytic in nature which help in digestion of carbohydrates, proteins and fats.They bring about hydrolytic splitting of complex organic substances into simple soluble and absorbablesubstances. For example, by the action of digestive enzymes, proteins are converted into amino acids.

Q.8 How is the small intestine designed to absorb digested food?

Ans. Small intestine is a long, tubular structure. Its inner wall is lined by epithelium which possess numerousfinger-like projections called villi. These villi not only increase the surface area for absorption but alsoreach deep into the lumen of intestine for maximum absorption of digested food. Villi possess bloodcapillaries and lymph vessels (lacteals) for quick transport of absorbed food.

NUTRITIONPage # 88


EXERCISE – I PRACTISE FOR FORMATIVE ASSESSMENT

Q.1 CO2 and O2 balance in atmosphere is due to

(A) Photorespiration (B) Photosynthesis (C) Respiration (D) Leaf anatomy

Q.2 During photosynthesis the oxygen in glucose comes from

(A) Water (B) Carbon dioxide

(C) Both from water and carbon dioxide (D) Oxygen in air

Q.3 With regards to natural eating habits, a human is

(A) An herbivore (B) A carnivore (C) An omnivore (D) A Granivore

Q.4 Muscular contractions of alimentary canal are

(A) Circulation (B) Deglutition (C) Peristalsis (D) Churning

Q.5 Which of the following regions of the alimentary canal of man does not secrete a digestive enzyme ?

(A) Oesophagus (B) Stomach (C) Duodenum (D) Mouth

Q.6 Saliva has the enzyme

(A) Pepsin (B) Ptyalin (C) Trypsin (D) Rennin

Q.7 Pepsin digests

(A) Proteins in stomach (B) Carbohydrates in duodenum

(C) Proteins in duodenum (D) Fats in ileum

Q.8 If the stomach did not produce any hydrochloric acid, which enzyme will not function ?

(A) Ptyalin (B) Trypsin (C) Pepsin (D) Collagenase

Q.9 Chief function of bile is

(A) To digest fat by enzymatic action

(B) To emulsify fat for digestion

(C) To eliminate waste product

(D) To regulate process of digestion

Q.10 Where is bile produced ?

(A) In gall bladder (B) In blood (C) In liver (D) In spleen

Q.11 Largest gland in human body is

(A) Liver (B) Pancreas (C) Pituitary (D) Thyroid

Q.12 The original function of the vertebrate stomach was

(A) Storage (B) Digestion

(C) Enzyme secretion (D) Absorption

NUTRITION Page # 89


FILL IN THE BLANKS

1. The whole process by which an organism obtains its food is referred to as .............

2. Other term for autotrophic nutrition is ..............

3. .................. manufacture their food from inorganic substances in the presence of energy derivedfrom the oxidation of simple inorganic compounds of iron, sulphur etc.

4. The process of utilization of absorbed food is known as ..............

5. Those organisms which depend on faecal matte of other organisms are known as ...............

6. Ligth reaction is also known as ............. phase.

7. The light intensity, at which the photosynthetic intake CO2 is called .............. .

8. Ingestion of food in Amoeba takes place by the process of ............

9. ................ is the type of digestion that occurs inside the lumen of digestive tract.

10. ................ are known as suicide bags of the cell.

ANSWER KEY

1. B 2. A 3. C 4. C 5. A 6. B 7. A

8. C 9. B 10. C 11. A 12. A

FILL IN THE BLANKS

1. Nutrition 2. a 3. Chemoautotrophs

4. Assimilation 5. Coprozoic heterotrophs

6. Photochemical phase 7. Compensation point 8. Phagocytosis

9. Intercellualr 10. Lysosomes

NUTRITIONPage # 90


EXERCISE – II PRACTISE FOR SUMMATIVE ASSESSMENT

Very Short Answer Type Questions

Q.1 Define heterotrophic nutrition.

Q.2 What are heterotrophs ?

Q.3 Which types of organisms are called consumers ?

Q.4 What is saprophytic nutrition ?

Q.5 Define saprophyte.

Q.6 Define a hervivore.

Q.7 What is carnivore ?

Q.8 Which type of animal is called omnivore ?

Q.9 What is the mode of nutrition in Amoeba ?

Q.10 What type of digestion occurs in Paramoecium ?

Short Answer Type Questions

Q.11 How do saprophytic organisms obtain their nourishment ?

Q.12 What is the importance of saprophytes ?

Q.13 What is the action of hydrochloric acid of gastric juice ?

Q.14 Name a digestive juice that has no enzymes. What is the role of this juice ?

Q.15 Name the various parts of large intestine. What is the role of large intestine ?

Long Answer Type Questions

Q.16 Explain the mechanism of nutrition of Amoeba with the help of suitable diagram.

Q.17 Describe the various types of heterotrophic nutrition.


Page # 91REAL NUMBERS

REAL NUMBERS1.1 BASIC CONCEPTS AND IMPORTANT RESULTS

(a) Natural numbers : Counting numbers are called natural numbers. We start counting from 1, so 1is the smallest natural number. A set of natural numbers is denoted by N. Thus,

N = {1, 2, 3, ...up to the numbers as possible as we can count}

(b) Whole numbers : Natural numbers together with zero are called whole numbers. A set of wholenumbers is denoted by W. Thus,

W = {0, 1, 2, 3, .....}

All natural numbers are whole numbers but all whole numbers are not natural numbers. Only thedifference between whole numbers and natural numbers is the number zero (0).

(c) Integers : All positive and negative natural numbers together with zero are called integers. A setof integers denoted by Z or I. Thus,

Z = {.... – 6, – 5, – 4, –3, – 2, –1, 0, 1, 2, 3, 4, 5, 6 ....}

(d) Rational numbers : A number of the form qp

, where p and q are integers and q 0 is called a

rational number. For example, 72

, 83

, 2, 0, etc., are rational number..

The decimal expansion of a rational number is either terminating or non-terminating repeating one.

(e) Irrational numbers : A number which is not a rational number, i.e., which cannot be written in

the form qp

, p and q Z or I and q 0, is known as an irrational number. For example,

2 , – 3 , 57 , 21

, 1 + 6 , etc., are irrational numbers.

The decimal expansion of an irrational number is non-terminating and non-repeating one.

(f) Real numbers : All rational and irrational numbers together make up a collection, called realnumbers.

Note : All natural numbers, integers, rational numbers and irrational numbers are real numbers.

1.2 EUCLID’S DIVISION ALGORITHM OR EUCLID’S DIVISION LEMMA

For any two given positive integers a and b, there exist unique whole numbers q and r such that:

a = b × q + r, where 0 r < b

52 2 41

Here, a is called the dividend, b the divisor, q the quotient and r is called the remainder. For example,when we divide 5 by 2, we get 2 as quotient and 1 as remainder

Here 5 = 2 × 2 + 1

Dividend = Divisor × Quotient + Remainder


Page # 92 REAL NUMBERS

Properties of Euclid’s Division Lemma :

(i) If an integer c be a divisor of each of the two given integers a and b, then we say that c is acommon factor of both a and b.

(ii) Let P be a prime number and if a,b, are integers such that abP

, then either aP

or bP

is a factor..

Note : If a prime number divides a product of integers, then it necessarily divides either of theintegers.

Obtaining HCF by Euclid Division Lemma :

Let a and b be two positive integers. If a = b × q + r, 0 r < b

Then HCF (a, b) = HCF (b, r)

where HCF(a, b) = Common division of a and b and

HCF (b, r) = Common division of b and r.

1.3 FUNDAMENTAL THEOREM OF ARITHMETIC

Every composite number can be expressed as a product of primes and this factorization is unique,apart from the order in which the prime factors occur.

Note : Any number of the form an will end with the digit zero if prime factors of an would contain5 and 2 as a prime factor, where n W.

1.4 THEOREMS ON RATIONAL NUMBERS

(i) Let x be a rational number whose decimal expansion terminates. Then x can be expressed in the form

qp

, where p and q are co-prime, and the prime factorization of q is of the form 2n5m, where n, m are

non-negative integer.

(ii) Let x = qp

be a rational number, such that the prime factorization of q is of the form 2n5m , where n,

m are non-negative integers. Then x has a decimal expansion which terminates.

(iii) Let x = qp

be a rational number such that the prime factorization of q is not of the form 2n5m, where

n, m are non-negative integers. Then x has a decimal expansion which is non-terminating repeating(recurring).

Note : HCF(p, q, r) × LCM(p, q, r) (p × q × r), where p, r and q are positive integers.

LCM(p, q, r) = p× q×r.HCF(p,q,r)

HCF(p,q).HCF(q,r).HCF(p,r)

HCF(p, q, r) = p×q×r.LCM(p,q,r)

LCM(p,q).LCM(q,r).LCM(p,r)



SOLVED PROBLEMSEx.1 Show that any positive odd integer is of the form 6q + 1, or 6q + 3 or 6q + 5, where q is some integer.Sol. Let us start with taking a, where a is any positive odd integer. We apply the division algorithm, with a

and b = 6. Since 0 r < 6, the possible remainders are 0, 1, 2, 3, 4, 5. That is, a can be 6q or 6q + 1,or 6q + 2, or 6q + 3, or 6q + 4, or 6q + 5, where q is the quotient. However, since a is odd, we do notconsider the cases 6q, 6q + 2 and 6q + 4 (since all the three are divisible by 2). Therefore, anypositive odd integer is of the form 6q + 1, or 6q + 3, or 6q + 5.

Ex.2 If a = 10 and b = 3. Then find q and r such that a = bq + r, o r < b.Sol. Clearly 10 = 3 × 3 + 1

q = 3 and r = 1 are required numbers.

Ex.3 Use Euclid’s division algorithm to find the HCF of 135 and 225.Sol. We start with the larger integer, that is, 225. Then by Euclid’s division algorithm we get:

225 = 135 × 1 + 90Now, consider the divisor 135 and the remainder 90 and apply the division algorithm again,we get :

135 = 90 × 1 + 45Now, consider the divisor 90 and the remainder 45 and apply the division algorithm again, we get.

90 = 45 × 2 + 0Notice that the remainder has become zero and we cannot proceed any further. The HCF of 90 and 45is 45 and we claim that the HCF of 225 and 135 is also 45.

Ex.4 An army contingent of 616 members is to march behind an army band of 32 members in a parade. Thetwo groups are to march in the same number of columns. What is the maximum number of columns inwhich they can march?

Sol. Hint : Find HCF of 616 & 32

Ex.5 Use Euclid's division lemma to show that the square of any positive integer is either of the form 3m or3m + 1 for some integer m.

Sol. Let a be any odd positive integer. We apply the division lemma with a and b = 3.Since 0 r < 3, the possible remainders are 0, 1 and 2. That is, a can be 3q, or 3q + 1, or3q + 2, where q is the quotient.Now, (3q)2 = 9q2

which can be written in the form 3m, since 9 is divisible by 3.Again, (3q + 1)2 = 9q2 + 6q + 1 = 3 (3q2 + 2q) + 1which can be written in the form 3m + 1 since 9q2 + 6q, i.e., 3(3q2 + 2q) is divisible by 3.Lastly, (3q + 2)2 = 9q2 + 12q + 4 = (9q2 + 12q + 3) + 1 = 3(3q2 + 4q + 1) + 1which can be written in the form 3m + 1, since 9q2 + 12q + 3, i.e., 3(3q2 + 4q + 1) is divisible by 3.Therefore, the square of any positive integer is either of the form 3m or 3m + 1 for some integer m.

Ex.6 Express each number as product of its prime factors :(i) 140 (ii) 156(iii) 3825 (iv) 5005 (v) 7429

Sol. (i) 140 (ii) 156

140

2

2

5

70

35

7

156

2

2

3

78

39

13

So, 140 = 2 × 2 × 5 × 7 = 22 × 5 × 7 So, 156 = 2 × 2 × 3 × 13 = 22 × 3 × 13(Rest Try your self)



Ex.7 Find the LCM and HCF of the following pairs of integers and verify that LCM × HCF = product of twonumbers.(i) 26 and 91 (ii) 510 and 92 (iii) 336 and 54

Sol. (i) 26 and 91

26

2 13

So, 26 = 2 × 13

91

7 13

So, 91 = 7 × 13Therefore, LCM (26, 91) = 2 × 7 × 13 = 182

HCF (26, 91) = 13Verification LCM × HCF = 182 × 13 = 2366 and 26 × 91 = 2366i.e., LCM × HCF = product of two numbers. (Rest Try your self)

Ex.8 Find the LCM and HCF of the following integers by applying the prime factorisation method.(i) 12, 15 and 21 (ii) 17, 23 and 29 (iii) 8, 9 and 25

Sol. (i) 12, 15 and 2112

2

2

6

3So, 12 = 2 × 2 × 3 = 22 × 3

15

3 5

So, 15 = 3 × 5

21

3 7

So, 21 = 3 × 7Therefore, HCF (12, 15, 21) = 3 ; LCM = (12, 15, 21) = 22 × 3 × 5 × 7 = 420

(Rest Try your self)Ex.9 Given that HCF (306, 657) = 9, find LCM (306, 657).

Sol. LCM (306, 657) = 306×657 306×657

=HCF (306, 657) 9 = 22338.

Ex.10 Prove that square of any odd integer is of the form 8k + 1, k an integer.Sol. For any odd integer is of the form 2m + 1 and (2m + 1)2 = 4m2 + 4m + 1

= 4 m (m + 1) + 1Now, m (m + 1) is alwyas even, say 2k, hence 4m(m + 1) = 4 × 2k

(2m + 1)2 = 8k + 1

Ex.11 Check whether 6n can end with the digit 0 for any natural number n.Sol. If the number 6n, for any natural number n, ends with digit 0, then it would be divisible by 5. That is,

the prime factorisation of 6n would contain the prime number 5. This is not possible because6n = (2 × 3)n = 2n × 3n ; so the only primes in the factorisation of 6n are 2 and 3 and the uniquenessof the Fundamental Theorem of Arithmetic guarantees that there are no other primes in the factorisationof 6n. So, there is no natural number n for which 6n ends with the digit zero.



Ex.12 Explain why 7 × 11 × 13 + 13 and 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5 are composite numbers.Sol. (i) 7 × 11 × 13 + 13 = (7 × 11 + 1) × 13

= (77 + 1) × 13= 78 × 13= (2 × 3 × 13) × 13 [ 78 = 2 × 3 × 13]= 2 × 3 × 132

Since, 7 × 11 × 13 + 13 can be expressed as a product of primes, therefore, it is a composite number.(Rest Try your self)

Ex.13 Prove that 5 is irrational.

Sol. Let us assume, to the contrary, that 5 is rational.So, we can find coprime integers a and b ( 0) such that

5 = ab

5 b = aSquaring on both sides, we get

5b2 = a2

Therefore, 5 divides a2.Therefore, 5, divides aSo, we can write a = 5c for some integer c.Substituting for a, we get

5b2 = 25c2

b2 = 5c2

This means that 5 divides b2, and so 5 divides b.Therefore, a and b have at least 5 as a common factor.But this contradicts the fact that a and b have no common factor other than 1.This contradiction arose because of our incorrect assumption that 5 is rational.

So, we conclude that 5 is irrational.Ex.14 There is a circular path around a sports field. Sonia takes 18 minutes to drive one round of the field,

while Ravi takes 12 minutes for the same. Suppose they both start at the same point and at the sametime, and go in the same direction. After how many minutes will they meet again at the starting point?

Sol. [Hint : Take LCM of 18 and 12]

Ex.15 Prove that 3 + 2 5 is irrational.Sol. Let us assume, to the contrary, that 3 + 2 5 is rational.

That is, we can find coprime integers a and b (b 0) such that 3 + 2 5 = ab

Therefore, ab

– 3 = 2 5

a–3bb

= 2 5

a–3b= 5

2b

a 3–

2b 2 = 5

Since a and b are integers, we get a 3–

2b 2 is rational, and so a – 3b 5

2b is rational.

But this contradicts the fact that 5 is irrational. This contradiction has arisen because of our

incorrect assumption that 3 + 2 5 is rational.

So, we conclude that 3 + 2 5 is irrational.



Ex.16 Show that 5 – 3 is irrational.

Sol. Suppose 5 – 3 is a rational number (say p)

Then 5 – 3 = p

5 – p = 3

Since p is a rational number and 5 is a rational

5 – p being the difference of two rational numbers is a rational number because the set of rationalnumbers are closed w.r.t. the operation of subtraction.

3 is a rational number But, it is an irrational number

Our supposition is wrong. Hence 5 – 3 irrational .

Ex.17 Prove that the following are irrationals :

(i) 12

(ii) 7 5 (iii) 6 2

Sol. (Try yourself)

Ex.18 Without actually performing the long division, state whether the following rational numbers will have aterminating decimal expansion or a non-terminating repeating decimal expansion.

(i) 13

3125(ii)

178

(iii) 64

455(iv)

151600

(v) 29

343

(vi) 3 2

232 5 (vii) 2 7 5

1292 5 7 (viii)

615

(ix) 3550

(x) 77

210

Sol. (i)13

3125= 5

135

Hence, q = 55, which is of the form 2n 5m (n = 0, m = 5). So, the rational number 13

3125 has a

terminating decimal expansion.

(ii)178

= 3172

Hence, q = 23, which is of the form 2n 5m (n = 3, m = 0). So, the rational number 178 has a terminating

decimal expansion.

(iii)64

455=

645 7 13

Hence, q = 5 × 7 × 13, which is not of the form 2n 5m. So, the rational number 64

455 has a

non-terminating repeating decimal expansion. (Rest Try your self)



Ex.19 Write down the decimal expansions of those rational numbers in Question 1 above which have terminatingdecimal expansions.

Sol. (i)13

3125

= 5

5 5 5

13 13×2=

5 5 ×2 = 5

416=

100.00416

(ii) 3

17 178 2

= 3 3

3 3 3

17×5 17×5=

2 ×5 10= 3

212510

= 2.125 (Rest Try your self)

Ex.20 The following real numbers have decimal expansions as given below. In each case, decide whether

they are rational, or not. If they are rational, and of the form pq , what can you say about the prime

factors of q?

(i) 43.123456789

(ii) 0.120 1200 12000 120000....

(iii) 43.123456789

Sol. (i) 43.123456789

Since, the decimal expansion terminates, so the given real number is rational and therefore of the form

pq . 43.123456789

= 431234567891000000000

= 9

4312345678910

= 9

43123456789(2×5)

= 9 9

431234567892 5

Hence, q = 29 59

The prime factorization of q is of the form 2n 5m, where n = 9, m = 9.

(ii) 0.120 1200 12000 120000....

Since, the decimal expansion is neither terminating nor non-terminating repeating, therefore, thegiven real number is not rational. (Rest Try your self)



Q.1 Prove that 2 is not a rational number or

there is no rational whose square is 2.

Q.2 Prove that 3 3 is irrational.

Q.3 Prove that 2 + 3 is irrational.

Q.4 Prove that 2+ 3 is irrational.

Q.5 Use Euclid's division lemma to show that the

square of any positive integer is either of the

form 3m or 3m +1 for some interger m.

Q.6 Show that one and only one out of n, n + 2 or

n + 4 is divisible by 3, where n is any positive

integer.

Q.7 Use Euclid's algorithm to find the HCF of 4052

and 12576.

Q.8 Find the HCF of 1848, 3058 and 1331.

Q.9 Using Euclid's division, find the HCF of 56, 96

and 404

Q.10 Find the L.C.M and H.C.F. of 1296 and 2520

by applying the fundamental theorem of

arithmetic method i.e. using the prime

factorisation method.

Q.11 Given that H.C.F. (336, 54) = 6. Find L.C.M.

(336, 54)

Q.12 Given that L.C.M. (150, 100) = 300, find H.C.F.

(150, 100).

Q.13 State Euclid's division lemma.

Q.14 State fundamental theorem of Arithmetic.

Q.15 For any two positive integers, state the relation

between the numbers, their H.C.F. and L.C.M.

Is this result true for three positive integers?

Q.16 Explain why 7 × 11 × 13 + 13 is a composite

number

Q.17 If qp

is a rational number (q 0), what is the

condition on q so that the decimal

representation of qp

is terminating?

Q.18 Write a rational number between 2 and 3 .

Q.19 Complete the missing entries in the following

factor tree?

23

7Box 2

Box 1

Q.20 Find the prime factors of 560.

Q.21 Find the missing numbers in the following

factorisation :

(box 4)

(box 3)

(box 2)

(box 1)

2

2

3

5 5

Q.22 Find the H.C.F. and L.C.M. of 17, 23, 37 by

applying prime factorisation method.

Q.23 Given that H.C.F. (14, 35) = 7, find L.C.M.

(14, 35).

UNSOLVED PROBLEMSEXERCISE – I



Q.24 Without performing long division, state

whether the number 45584 will have a

terminating or a non-terminating but repeating

decimal representation.

Q.25 Write down the decimal representation of

21077

.

Q.26 The following real numbers have decimal

expansion as given below. In each case

decide whether it is rational or not. If rational,

what can be said about the prime factors of

denominator.

(i) 4.59

(ii) 0.13013001300013000013……

(iii) 60120.0

Q.27 Find two irrational numbers between 0.1 and

0.12.

Q.28 Find a rational number and also an irrational

number between the numbers.

a = 0.101001000100001……,

b = 0.1001000100001……

Q.29 Show that any positive odd integer is of the

form 4q + 1 or 4q + 3, where q Z+.

Q.30 Without actually performing the long division,

state whether the rational number 160017 will

have terminating or non-terminating but

repeated decimal representation.

Q.31 Examine whether the following numbers are

rational or irrational :

(i) 2

32 (ii) 2

32

(iii) 3333 (iv) 3

32

Q.32 Show that p2 – 1 is divisible by 8, where p is

an odd positive interger.

Q.33 Prove that 5 is an irrational number..

Q.34 Use Euclid's division lemma to show that the

cube of any positive integer is of the form 9m,

9m + 1 or 9m + 8.

Q.35 Check whether 7n can end with digit 0, for any

natural number n.

Q.36 If H.C.F. (65, 117) is expressed in the form

65m + 117n, then find the value of m.

Find the g.c.d. of the following pairs of polynomials

Q.37 4(x – 3) 2 (x – 1) (x + 1)3 and 6(x – 1)2

(x + 1)2 (x + 7)

Q.38 (x – 2)2 (x + 3) (x – 4) and (x – 2) (x + 2) (x –

5)

Q.39 (2x – 7) (3x + 4) and (2x – 7)2 (x + 3)

Q.40 (3x – 2)2 (2x + 3)3 (x – 1) and (3x – 2)3 (2x +

3) (x – 1)3

Q.41 (x – 1) (x + 1)3 and (x – 1)3 (x + 1)



Q.42 (x + 4)2 (x – 3)3 and (x – 1) (x + 4) (x – 3)2

Q.43 24(x – 3) (x – 2)2 and 15(x – 2) (x – 3)3

Q.44 16 – 4x2 and x2 + x – 6

Q.45 xy – y and x4y – xy

Q.46 2x2 – 7x + 3 and 3x2 – 7x – 6

Q.47 x3 + 64 and x2 – 16

Q.48 x3 + 2x2 – 3x and 2x3 + 5x2 – 3x

Q.49 22x(x + 1)2 and 36x2(2x2 + 3x + 1)

Q.50 3 + 13x – 30x2 and 25x2 – 30x + 9

Q.51 (x3 – y3) and (x4 + x2y2 + y4)

Q.52 2x2 + 7xy + 3y2 and 2x2 + 6xy + x + 3y

Q.53 56(x6y2 – x2y6) and 72(x5y3 + 3y5x3 + 2y7x)

Q.54 54(x3 + 8y3) and 90(x3 + 7x2y + 16xy2 + 12y3)

Q.55 (4x4 + y4) and (2x3 – xy2 – y3)

Q.56 x3 – y3; x3 y – y4 and y2(x – y)2 (x2 + xy + y2)

Q.57 (2x2 – 3xy)2; (4x – 6y)3 and (8x3 – 27y3)

Q.58 (4x4 + y4); (2x3 – xy2 – y3) and (2x2 + 2xy + y2)

Q.59 x4 – x3 + x – 1 and x4 + x2 + 1

Q.60 (8x6 – 32x5 + 128x3 – 128x2) and (12x6 – 36x5 +

48x3)

Q.61 (x3 – x2 – x + 1) and (x4 – 2x3 + 2x – 1)

Q.62 2x2y(x2 – y2) and 35 xy2(x – y)

Q.63 (x2 + 4x – 21) and (x3 + 7x2 – 9x – 63)

Q.64 (6x4 – 13x3 + 6x2) and (8x4 – 36x3 + 54x2 – 27x)

Q.65 (x3 – x2 – x – 2) and (x3 + 3x2 – 6x – 8)

Q.66 (4x5 + 16x4 – 44x2 – 24x) and (2x5 – 6x3 + 2x)

Q.67 (3x3 – 14x2 + 9x + 10) and (15x3 – 34x2 + 21x – 10)

Q.68 4x2(x2 – a2) and 9x2(x3 – a3)

Q.69 2(a2 – b2) and 3(a3 – b3)

Q.70 (x2 + 3x – 4) and (x3 – 2x2 – 2x + 3)

Q.71 12(x4 – 25) and 8(x4 + 4x2 – 5)

Q.72 Find the values of a and b so that the polynomial

x3 + ax2 + bx – 42 is divisible by x2 – x – 6.

Q.73 Find the values of a and b so that the polynomial x3

+ ax2 + bx – 6 is completely divisible by x2 – 4x – 3.

Q.74 Find the values of a and b so that the polynomial

f(x) = 3x3 + ax2 – 13x + b is divisible by x2 – 2x – 3.

Q.75 Find the GCD of the polynomials

(i) 12(x3 + x2 + x + 1) and 18(x4 – 1).

(ii) 12(3x4 – 14x3 – 5x2) and 30(3x5 + 4x4 + x3)

Q.76 Find the GCD of the polynomials :

(i) x3 + 2x2 – 3x and 2x3 + 5x2 – 3x

(ii) 4(x4 – 1) and 6(x3 – x2 – x + 1)

Q.77 If x2 – x – 6 is the GCD of the expressions (x + 2)

(2x2 + ax + 3) and (x – 3) (3x2 + bx + 8).

Find the values of a and b.


2(x4 – y4), 3(x2 + 2x2y – xy2 – 2y3).



Q.79 If (x2 – x – 2) is the GCD of the expressions

(x – 2) (2x2 + ax + 1) and (x + 1) (3x2 + bx + 2),

find the values of a and b.


(i) p(x) = 45(2x4 – x3 – x2) and q(x) = 75(8x5 + x2).

(ii) p(x) = 36(3x4 + 5x3 – 2x2) and q(x) = 54(27x4 – x).

(iii) p(x) = 42(2x3 – 5x2 – 3x) and q(x) = 60(8x4 + x).

Q.81 (x + 1) (x – 4) is the g.c.d. of the polynomials

(x – 4) (2x2 + x – a) and (x + 1) (2x2 + bx – 12).

Find a and b.

Q.82 (x – 3) is the g.c.d. of x3 – 2x2 + px + 1 and

x2 – 5x + q. Find the 6p + 5q.

Q.83 For what value of k, the g.c.d. of x2 + x –

(2k + 2) and 2x2 + kx – 12 is x + 4 ?

Q.84 If G.C.D. of (x – 5) (x2 – x – a) and (x – 4)

(x2 – 2x – b) is (x – 4) (x – 5), find the values

of a, b.

Q.85 Find the values of k for which the g.c.d. of

x2 – 2x – 24 and x2 – kx – 6 is x – 6.

Q.86 Find the H.C.F. of x4 – 1 and x3 + x2 + x + 1.

Q.87 Find the value of a and b so that the

polynomials P(x) and Q(x) have (x + 1)

(x – 2) as their HCF :

P(x) = (x2 + 3x + 2) (x2 + x + a)

Q(x) = (x2 – 3x + 2) (x2 – 3x + b)

Q.88 Find the values of a and b such that the

polynomials. P(x) and Q(x) have (x + 3)

(x – 2) as their HCF :

P(x) = (x2 – 4x – 21) (x2 – 4x + a)

Q(x) = (x2 – 5x + 6) (x2 – 4x + b)

Q.89 If (x ) is the GCD of ax2 + bx + c and

bx2 + cx + a, prove that either

a = 0 or a3 + b3 + c3 = 3abc.

Q.90 If (x ) is the GCD of ax2 + bx + c and

cx2 + bx + a, prove that

a + b + c = 0 or a – b + c = 0

Q.91 If the polynomials x2 – 4mx + 2 and

3x2 – 2mx – 4 have a common linear factor,

find the values of m.

Q.92 If (x ) is the HCF of px2 + qx + c and ax2 + bx

+ c, prove that (p a) = (b – q).

Q.93 Find the HCF (GCD) of the polynomials :

(i) (x – 3) (x + 5)2, (x + 5) (x + 7)2 and (x + 2)

(x + 5)3

(ii) 2(x – 7) (x + 7)2, 4(x – 7)2 (x + 8) and

8(x2 – 49)

(iii) x2 – 1, x4 – 1 and (x – 1)2

(iv) 4(x + 2), 8(x + 3) and 16(x + 4)

(v) 3(x + 3), 5(x + 3) (x + 5) and 7(x + 4)

Q.94 Fine what value(s) of k is the HCF of x2 + x –

(2k + 2) and 2x2 + kx – 12, (x + 4) ?



Q.95 If the HCF of the polynomials

f(x) = (x – 1) (x2 + 3x + a) and,

g(x) = (x + 2) (x2 + 2x + b) is (x – 1) (x + 2)

find a and b.

Q.96 Find a and b so that the polynomials

f(x) = (x2 + 3x + 2) (x2 + 2x + a)

and g(x) = (x2 + 7x + 12) (x2 + 7x + b) may

have (x + 1) (x + 3) as their HCF.

Q.97 If (x – 2) is a factor of x2 + ax + b and

a + b = 1, find the values of a and b.

Q.98 If (x + 3) (x – 2) is the GCD of f(x) = (x + 3) (2 x2

– 3x + a) and, g(x) = (x – 2) (3x2 + 10x – b)

find the values of a and b.

7. HCF = 4 8. HCF = 11 9. HCF = 4

10. HCF = 72, LCM = 45360 11. LCM = 3024

12. HCF = 50 15. HCF × LCM = a × b, No

16. More than 2 factors

17. Factors of q are in the form of 2m or 5n or 2m × 5n

18. 1.5 19. 21, 42

20. 24 × 5 × 7 21. 25, 75, 150, 300

22. 1,14467 23. 70 24. Non-terminating

25. 0.3 6

26. (i) Rational (ii) Not Rational (iii) Rational

27. 0.101001000...., 0.1121231234....

28. 0.1002, 0.100212112111....

30. Terminating

31. (i) Irrational (ii) Irrational

(iii) Rational (iv) Irrational

35. Not 36. m = 2, n = –1

37. 2(x – 1) (x + 1)2 38. (x – 2)

39. (2x – 7) 40. (3x – 2)2 (2x + 3) (x – 1)

41. (x – 1) (x + 1) 42. (x + 4) (x – 3)2

43. 3(x – 3) (x – 2) 44. (x – 2)

45. (x – 1)y 46. (x – 3) 47. (x + 4)

48. x(x + 3) 49. 2x(x + 1) 50. (5x – 3)

51. x2 + xy + y2 52. x + 3y

53. 8xy2(x2 + y2) 54. 18(x + 2y)

55. 2x2 + 2xy + y2 56. x3 – y3 57. 2x – 3y

58. 2x2 + 2xy + y2 59. x2 – x + 1 60. 4x2(x – 2)

61. (x – 1)2 (x + 1) 62. xy(x – y)

63. (x + 7) (x – 3)2 64. x(2x – 3) 65. (x – 2)

66. 2x(x2 – x – 1) 67. (3x – 5) 68. x2(x – a)

69. (a – b) 70. (x – 1) 71. 4(x2 + 5)

72. a = 6, b = 13 73. a = 6, b = 11

74. a = 4, b = 6

75. (i) 6(x + 1) (x2 + 1) (ii) 6x2(3x + 1)

76. (i) x(x + 3) (ii) 2(x2 – 1)

77. a = 7, b = 10 78. x2 – y2 79. a = 3, b = 7

80. (i) 15x2(2x + 1) (ii) 18x (3x – 1) (iii) 6x(2x + 1)

81. a = 1, b = 5 82. 10 83. k = 5

84. a = 12, b = 15 85. k = 5 86. (x + 1) (x2 + 1)

87. a = 6, b = 4 88. a = 4, b = 21

91. m = ±1

2

93. (i) x + 5 (ii) 2(x – 7) (iii) x – 1 (iv) 4 (v) 1

94. 5 95. a = 2, b = 3

96. a = 3, b = 6 97. a = 3, b = 6

98. a = 2, b = 3.

ANSWER KEY



Questions Carrying 1 Mark

Q.1 If pq

is a rational number (q 0), what is

condition of q so that the decimal representation

of pq

is terminating? [Delhi-2008]

Q.2 Write a rational number between 2 and 3 . [AI-2008]

Q.3 Complete the missing entries in the followingfactor tree : [Foreign-2008]

2

3

7

Q.4 The decimal expansion of the rational number

4 3

432 ·5

, will terminate after how many places

of decimals? [Delhi-2009]

Q.5 Find the [HCF × LCM] for the numbers 100and 190. [AI-2009]

Q.6 Find the [HCF × LCM] for the numbers 105and 120. [AI-2009]

Q.7 Write whether the rational number 51

1500 will

have a terminating decimal expansion or a non-terminating repeating decimal expansion.

[Foreign-2009]

Q.8 The HCF and LCM of two numbers are 9 and360 respectively. If one number is 45, writethe other number. [Foreign-2009]

Questions Carrying 3 Marks

Q.9 Show that 5 – 2 3 is an irrational number.. [Delhi-2008]

Q.10 Show that 2 – 3 is an irrational number.. [Delhi-2008]

Q.11 Show that 5 + 3 2 is an irrational number.. [Delhi-2008]

Q.12 Prove that 3 is an irrational number..[Delhi -2009/AI-2008]

Q.13 Use Euclid's Division Lemma to show that thesquare of any positive integer is either of theform 3m or 3m + 1 for some integer m.

[Foreign-2008/AI-2008]

Q.14 Prove that 2 is an irrational number..[Delhi-2009/AI-2008]

Q.15 Prove that 5 is an irrational number..[Delhi-2009/AI-2008]

Q.16 Prove that 3 + 2 is an irrational number.. [AI-2009]

Q.17 Prove that 3 + 5 2 is an irrational number.. [AI-2009]

Q.18 Show that the square of any positive oddintegers is of the form 8m + 1, for some integerm. [Foreign-2009]

Q.19 Prove that 7 + 3 2 is not a rational number..[Foreign-2009]

BOARD PROBLEMSEXERCISE – II

ANSWER KEY

1. q = 2n × 5m, where n and m are whole

numbers.

2. 2 = 1.41......., 3 = 1.73.....

One rational no. between 2 and 3 is 1.5.

3.

2

3

7

42

21

4. After 4 decimal; 4 3

432 ·5

= 43

2000 = 0.0215

5. HCF × LCM = 100 × 190 = 19000

6. HCF × LCM = 105 × 120 = 12600

7.51 17

1500 500; 500 = 22 × 53 (2m · 5n). So, it

has terminating expansion.

8. Other number = 9 360

7245



MULTIPLE CHOICE QUESTIONSEXERCISE – IIIQ.1 A rational number between

41 and

31 is

(A) 247

(B) 0.29

(C) 4813 (D) all the above

Q.2 An irrational number is(A) a terminating and nonrepeating decimal(B) a nonterminating and non repeating decimal(C) a terminating and repeating decimal(D) a nonterminating and repeating decimal

Q.3 Which of the following statements is true(A) Every point on the number line represents

a rational number(B) Irrational numbers cannot be represented

by points on the number line

(C) 722

is a rational number

(D) None of theseQ.4 The set of real numbers does not satisfy the

property of(A) multiplicative inverse

(B) additive inverse(C) multiplicative identity(D) none of these

Q.5 If m is an integer, then square of any positiveinteger is of the form :

(A) 2m + 1 (B) 2 m or 3m(C) 3m or 3m + 1 (D) 2m + 1 or 3m + 1

Q.6 If 'm' is an irrational number then '2m' is(A) a rational number(B) an irrational number(C) a whole number(D) a natural number

Q.7 The value of 3 is(A) 0.414 (B) 2.256(C) 1.732 (D) none

Q.8 The sum of a rational and an irrational number.(A) an irrational number(B) a rational number(C) an integer(D) a whole number

Q.9 The product of two irrationals is(A) a rational number(B) an irrational number

(C) either A or B(D) neither A nor B

Q.10 The value of 21.434.1 is

(A) 99133 (B) 90

371

(C) 9905169

(D) 9905411

Q.11 Which of the following statements is false?(A) Every fraction is a rational number(B) Every rational number is a fraction(C) Every integer is a rational number(D) All the above

Q.12 An irrational number is :(A) a terminating and non-repeating decimal(B) a non-terminating and non-repeating

decimal(C) a terminating and repeating decimal(D) a non-terminating and repeating decimal

Q.13 7 × 11 × 13 + 13 and 7 × 6 × 5 × 4 × 3 ×2 × 1 + 5 are(A) composite numbers(B) whole number(C) prime numbers(D) none of these

Q.14 HCF of two numbers is 113, their LCM is 56952.If one number is 904, the other number is :(A) 7719 (B) 7119(C) 7791 (D) 7911

Q.15 For what least value of n (where n is a naturalnumber), (24)n is divisible by 8?(A) 0(B) –1(C) 1(D) no value of x possible

Q.16 is(A) a rational(B) an irrational(C) both (A) and (B)(D) sometimes rational, sometimes irrational

Q.17 Expressing 583.0 as a rational number, we get :

(A) 100358 (B) 999

358

(C) 990355 (D) None of these

Q.18 Which of the following numbers has theterminating decimal representation ?

(A) 71 (B) 3

1

(C) 53 (D) 6

17



Q.19 Missing numbers in the following factor treeare : x

2 y

2 y

(A) x = 34, y = 68 (B) y = 34, x = 68(C) y = 34, x = 34 (D) y = 68, x = 68

Q.20 A lemma is an axiom used for proving :(A) other statement(B) no statement(C) contradictory statement(D) none of these

Q.21 If 223

1b ,223

1a , then the value of

a2 + b2 is :(A) 34 (B) 35(C) 36 (D) 37

Q.22 The set of all irrational number is closed for(A) addition (B) multiplication(C) division (D) none of these

Q.23 The additive inverse of ba is

(A) ba (B) a

b

(C) ab

(D) ba

Q.24 Multiplicative inverse of '0' is

(A) 01

(B) 0

(C) does not exist (D) none of these

Q.25 If 5 = 2.236 and 3 = 1.732, then the value

of 35

735

2 is

(A) 14 (B) 14.39(C) 14.392 (D) 16

Q.26 A rational number can be expressed as aterminating decimal if the denominator hasfactors(A) 2 or 5 (B) 2, 3 or 5(C) 3 or 5 (D) none of these

Q.27 Express 0.75 as rational number.

(A) 9975 (B) 90

75

(C) 43 (D) None

Q.28 Express 75.0 as rational number..

(A) 9075 (B)

3325

(C) 43 (D) None

Q.29 Express 583.0 as rational number

(A) 1000358 (B)

999358

(C) 990355 (D) All

Q.30 Which of the following statements is true?

(A) 1311

119

97

75

(B) 75

97

119

1311

(C) 119

97

1311

75

(D) 97

1311

119

75

Q.31 ______ is a series of well defined steps, whichgives a procedure for solving a type of problem.(A) Theorem (B) Statment(C) Algorithm (D) None of these

Q.32 Euclid's division algorithm can be applied to :(A) only positive integers(B) only negative integers(C) all integers(D) none of these

Q.33 Expressing 0.625 as a rational number, we get :

(A) 1000

5.62 (B) 85

(C) 100625 (D) None of these

Q.34 A rational number in its standard from can beexpressed as a terminating decimal, if thedenominator has factors :(A) 2 or 5 (B) 2, 3 or 5(C) 3 or 5 (D) None of these

Q.35 63.0 as a fraction in the simplest form is :

(A) 9036

(B) 10036

(C) 3011 (D) 90

33



Q.36 542.0 as a fraction in the simplest form is

(A) 5514 (B) 1000

254

(C) 16542 (D) 495

126

Q.37 Representation of 6.3 as a fraction in thesimplest form is :

(A) 1311 (B) 3

11

(C) 1036

(D) 113

Q.38 65 is :

(A) a rational number(B) an irrational number(C) can't say(D) both (A) and (B)

Q.39 16.0 as rational number in the simplest form is :

(A) 100016

(B) 9916

(C) 10016 (D) 50

8

Q.40 0.1010010001 …… is :(A) a rational number(B) a repeating decimal number(C) an irrational number(D) both (A) and (C)

Q.41 The value of 4 –

412

13

11

5 is

(A) 3140

(B) 94

(C) 81

(D) 4031

Q.42 The sum of the additive inverse andmultiplicative inverse of 2 is

(A) 23

(B) 23

(C) 21 (D) 2

1

Q.43 If 6 = 2.449 then the value of 3223

is close

to(A) 1.225 (B) 0.816(C) 0.613 (D) 2.449

Q.44 The value of 5555 is

(A) 0(B) 5(C) can't be determined(D) none

Q.45 The greatest among the following is

I. 3 728.1 II. 1313

III. 2

21 IV. 8

17

(A) I (B) IV(C) II (D) III

Q.46 Which of the following is not a rational number?

(A) 2 (B) 4

(C) 9 (D) 16Q.47 Set of natural numbers is a subset of

(A) set of even numbers(B) set of odd numbers(C) set of composite numbers(D) set of real numbers

Q.48 The quotient of )323()323( is :

(A) a rational(B) an irrational(C) both (A) and (B)(D) either (A) or (B)

Q.49 Which of the following is a rational number

(A) 5 (B) 6

(C) 8 (D) 9Q.50 The sum of two rational number is always

(A) an irrational number(B) a rational number(C) a fraction(D) none of these

Q.51 The product of a rational and an irrationalnumber is always :(A) a irrational number(B) a rational number(C) a fraction(D) none of these

Q.52 The sum of a rational number and an irrationalnumber is always :(A) an irrational number(B) a rational number(C) an integer(D) a whole number



Q.53 The product of two irrational number is :

(A) a rational number

(B) an irrational number

(C) either (A) or (B)

(D) neither (A) nor (B)

Q.54 21

is :

(A) a rational

(B) an irrational

(C) both (A) and (B)

(D) none of these

Q.55 If q is some integer, then any positive oddinteger is of the form :

(A) q – 1

(B) 2q

(C) 4q + 1 or 4q – 1

(D) 4q + 1 or 4q + 3

Q.56 If p : All integers are rational number and q :Every rational is an integer, then which of thefollowing statements is correct?

(A) p is false and q is true

(B) p is true and q is false

(C) both p and q are true

(D) both p and q are false

Q.57 For any two rational number x and y, which ofthe following properties are correct?

(i) x < y (ii) x = y (iii) x > y

(A) only (i) and (ii) are correct

(B) only (ii) and (iii) are correct

(C) only (ii) is correct

(D) All (i), (ii), (iii) are correct

Q.58 If A : Every whole number is a natural numberand R : 0 is not a natural number, then whichof the following statement is true?

(A) A is false and R is the correct explanation of A

(B) A is true and R is the correct explanation of A(C) A is true and R is false

(D) both A and R are true

Q.59 If x = )83( , then the value of 22

x1x is :

(A) 24 (B) 25(C) 30 (D) 34

Q.60 The numbre 26 26 is

(A) rational (B) irrational(C) can't say (D) none

Q.61 In a morning walk three persons step off together.Their steps measures 80 cm, 85 cm and 90 cmrespectively. The minimum distance each shouldwalk so that they can cover the distance incomplete step is.(A) 122 m 40 cm (B) 132 m 60 cm(C) 125 m 31 cm (D) 120 m 40 cm

Q.62 The number 2

32 is

(A) rational number(B) irrational number(C) can't say(D) none

Q.63 The number yx yx ,

where x, y > 0 is(A) rational (B) irational(C) both (D) none

Q.64 Two irrational numbers between2 and 3 are :

(A) 41

21

6 ,2 (B) 61

41

3 ,3

(C) 41

81

3 ,6 (D) none of these

Q.65 Two tankers contain 850 litres and 680 litresof petrol respectively. The maximum capacityof a container which can measure the petrolof either tanker in exact number of times is :(A) 160 litres (B) 168 litres(C) 170 litres (D) 180 litres

Q.66 Rational number between 2 and 3 is

(A) 232 (B) 2

32

(C) 1.5 (D) 1.8Q.67 The irrational number between 2 and 3 is

(A) 2 (B) 3

(C) 5 (D) 11

Q.68 The number 3333 is

(A) rational (B) irrational(C) both (D) can't say

Q.69 The rational number between 21 and

31 is

(A) 52

(B) 51

(C) 53

(D) 54



Q.702323

2323 is equal to :

(A) 15 (B) 16(C) 10 (D) 24

Q.71 463

1008 is equal to :

(A) 1 (B) 2(C) 4 (D) 6

Q.72 7 5 is :

(A) an irrational(B) a rational(C) neither (A) nor (B)(D) all of the above

Q.73 )26( is :

(A) a rational (B) an irrational(C) an integer (D) not real

Q.74 The greatest number of 6 digits exactly divisibleby 24, 15 and 36 is :(A) 999998 (B) 999999(C) 999720 (D) 999724

Q.75 523 732121

is

(A) a terminating decimal number(B) a non-terminating repeating decimal(C) a rational number(D) both (B) and (C)

Q.76 The largest number of four digits exactlydivisible by 12, 15, 18 and 27 is :(A) 9720 (B) 9820(C) 9920 (D) 9930

Q.77 251

561

671

781

831

is

(A) 0 (B) 1(C) 2 (D) 5

Q.78 If a = 2 and b = 3, then a

b1

a1 is equal to :

(A) 94

(B) 3625

(C) 17 (D) 1731

Q.79 The domain of the function

ƒ(x) = 5x4x + |x| + x2

(A) R – {4} (B) R – {4, 5}(C) [5, ) (D) R

Q.80 The equivalent rational form of 6.17 is

(A) 3

53 (B) 5

88

(C) 2544

(D) none

Q.81 If p : Every fraction is a rational number andq : Every rational number is a fraction, thenwhich of the following is correct?(A) p is true and q is false(B) p is false and q is true(C) Both p and q are true(D) Both p and q are false

Q.82 Which of the following is a rational number(s) ?

(A) 92 (B)

74

(C) 173

(D) All the three

Q.83 03 is a ____ .

(A) positive rational number

(B) negative rational number(C) either positive or negative rational number

(D) neither positive nor negative rationalnumber

Q.84 If x, y, z be rational number such that x > yand z < y then .......

(A) z > x (B) z < x(C) y < z (D) y > x

Q.85 If A : The quotient of two integers is always a

rational number and R :01 is not rational, then

which of the following statement is true(A) A is true and R is the correct explanation of A(B) A is false and R is the correct explanation of A(C) A is true and R is false(D) Both A and R are false

Q.86 For what least value of n, where n is a naturalnumber, 5n is divisible by 3?(A) 1 (B) 0(C) 2 (D) no value of n is possible

Q.87 Which one is the correct alternative of thedecimal representation of an irrational number ?(A) non - terminating, non-repeating(B) terminating(C) termiating, repeating(D) non-terminating, repeating



1. D 2. B 3. D 4. D

5. C 6. B 7. C 8. A

9. C 10. D 11. B 12. B

13. A 14. B 15. C 16.

17. C 18. C 19. B 20. A

21. 22. D 23. A 24. C

25. C 26. A 27. C 28. B

29. C 30. A 31. C 32. C

33. B 34. A 35. C 36. A

37. B 38. B 39. B 40. C

41. C 42. B 43. A 44. B

45. D 46. A 47. D 48. B

49. D 50. B 51. A 52. A

53. C 54. B 55. D 56. B

57. D 58. A 59. D 60. A

61. A 62. B 63. A 64. C

65. C 66. C 67. C 68. B

69. C 70. C 71. B 72. A

73. B 74. C 75. D 76. A

77. D 78. B 79. C 80. A

81. A 82. D 83. D 84. B

85. B 86. D 87. A 88. B

89. B 90. B 91. D 92. C

93. D 94. D

ANSWER KEY

Q.88 The value of 21.434.1 is

(A) 990133 (B) 290

371

(C) 9905169 (D) 990

5411

Q.89 Which of the following numbers is the fourthpower of a natural number? [NTSE 2013]

(A) 6765207 (B) 6765201

(C) 6765206 (D) 6765209

Q.90 Two candles are of different lengths andthicknesses. The short and the long onescan burns respectively for 3.5 h and 5 h.After burning for 2 h, the lengths of thecandles become equal in length. Whatfraction of the long candle’s height was theshort candle initially? [NTSE 2013]

(A) 27

(B) 57

(C) 35

(D) 45

Q.91 I left home for bringing milk between 7 amand 8 am. The angle between the hour handand the minute hand was 90°. I returnedhome between 7 am and 8 am. Then, alsothe angle between the minute hand andhour hand was 90°. At what time (nearestto second) did I leave and return home?

[NTSE 2013]

(A) 7 h 18 min 35 s and 7 h 51 min 24 s(B) 7 h 19 min 24 s and 7 h 52 min 14 s(C) 7 h 20 min 42 s and 7 h 53 min 11 s(D) 7 h 21 min 49 s and 7 h 54 min 33 s

Q.92 The square of an odd integer must be of theform [NTSE 2013]

(A) 6n + 1

(B) 6n + 3

(C) 8n + 3

(D) 4n + 1 but may not be 8n + 1

Q.93 2 2a b b a is [NTSE 2013]

(A) always zero

(B) never zero

(C) positive if and only, if a > b

(D) positivel only, if a b

Q.94 Which of the following is an irrationalnumber? [NTSE 2013]

(A) 41616

(B) 23.232323

(C)

3 31 3 1 3

3

(D) 23.10100100010000.....

WORK, LIFE AND LEISUREPage # 110


CHARACTERISTICS OF THE CITYTown and cities that first appeared along river valleys, such as Ur, Nippur and Mohenjodaro, were largerin scale than other human settlements. Ancient cities could develop only when an increase in foodsupplies made it possible to support a wide range of non-food producers. Cities were often the centresof political power, administrative network, trade and industry, religious institutions, and intellectualactivity, and supported various social groups such a artisans, merchants and priests.Cities themselves can vary greatly in size and complexity. They can be densely settled modern-daymetropolises, which combine political and economic functions for a entire region, and support verylarge populations. Or they can be smaller urban centres with limited functions.

1. The industrialisation and the rise of the Modern city in England:The early industrial cities of Britain such as Leeds and Manchesterattracted large number of migrants to the textile mills set up in thelate eighteenth century. In 1851, more than three-quarters of theadults living Manchester were migrants from rural areas.Now let us look at London. By 1750, one out of every nine peopleof England and Wales lives in London. It was a colossal city with apopulation of about 675000. Over the nineteenth century. Londoncontinued to expand. Its population multiplied fourfold in the70 years between 1810 and 1880, increasing 1 million to about 4million.

The growth of London, a map showing its population

in four different years.

2. The city of London : The city of London was a powerful magnetfor migrant populations, even though it did not have large factories.‘Nineteenth century London’, says the historian Gareth StedmanJones, ‘was a city of clerks and shopkeepers, of small masters andskilled artisans, of growing number of semi skilled and sweatedoutworkers, of soldiers and servants, of casual labourers, streetsellers, and beggar’. Apart from the London dockyards, five majortypes of industries employed large numbers clothing and footwear,wood and furniture, metals and engineering, printing and stationary,and precision products such as surgical instruments, watches,and objects of precious metal. During the First World War(1914-18) London began manufacturing motor cars and electricalgoods, and the number of large factories increased until theyaccounted for nearly one-third of all jobs in the city.In the mid-nineteenth century. Henry Mayhew wrote several volumes on the land on labour andcompiled long lists of those who made living from crime. Many of whom he listed as ‘criminals’ were infact poor people who lived by stealing lead from roofs, food from shops, lumps of coal, and clothesdrying on hedges. There were others who were more skilled at their trade, expert at their jobs.They were cheats and tricksters, pickpockets and petty thieves crowding the streets of London.In an attempt to discipline the population, the authorities imposed high penalties for crime and offeredwork to those who were considered the ‘deserving poor’.With technological developments, women gradually lost their industrial jobs, and were forced to workwithin household. The 1861 census recorded a quarter of million domestic servants in London of whomthe vast majority were women, many of them recent migrants. A large number of women used theirhomes to increase family income by taking in lodgers or through such activities as tailoring, washing ormatchbox making. However, there was a change once again in the twentieth century.As women got employment in wartime industries and offices, they withdraw from domestic service.Large numbers of children were pushed into low-pad work, often by their parents. Andrew Means, aclergyman who wrote The Bitter Cry of outseast London in the 1880s, showed why crime was moreprofitable than labouring in small underpaid factories. A child seven years old is easily known to make10 shillings 6 pence a week from thieving ... Before he can gain as much as the young thief (a boy)must make 56 gross of matchboxes a week, or 1,296 a day. It was only after the passage of thecompulsory Elementary Education Act in 1870 and the factory acts beginning from 1902, that childrenwere kept out of industrial work.

WORK, LIFE & LEISURE

WORK, LIFE AND LEISURE Page # 111


3. Housing : For a while the better-off city dwellers continued to demand that slums simply be clearedaway. But gradually a larger and larger number of people began to recognise the need for housing forthe poor. What were the reasons for this increasing concern ?

A Stranger's Home, The Illustrated London New, 1870.First, the vast mass of one-room houses occupied by the poor were seen as a serious threat to publichealth; they were overcrowded, badly ventilated lacked sanitation.Second, there were worries about fire hazards created by poor housing.Third, there was a widespread fear of social disorder, especially after the Russian Revolution in 1917.Workers mass housing schemes were planned to prevent London poor from turning rebellious.

Rat-trap seller, cartoon by Rowlandson, 1799

A London slum in 1889.

For the poor, the street often was the only place for rest, leisure and fun. The IllustratedLond News, 1856.



4. Clearing London : The congestion in the nineteenth-centuryindustrial city also led to a yearning for clean country air. Manywealthy resident of London were able to afford a holiday home inthe countryside. Demands were made for new ‘lungs’ for the city,and some attempts were made to bridge the difference betweencity and countryside through such ideas as the Green Belt aroundLondon.

New Earswick, a garden suburb

Between two world wars (1919-39) the responsibility for housingthe working classes was accepted by the British state, and amillion houses, most of them single-family cottages, were built bylocal authorities. Meanwhile, the city had extended beyond the

range where people could walk to work, and the development ofsuburbs made new forms of mass transport absolutely necessary.

5. Transport in the City : The very first section of the Undergroundin the world opened on 10 January 1863 between Paddington and

Farrington Street in London. On that day 10,000 passengers werecarried, with trains running every ten minutes. By 1880 the expandedtrain service was carrying 40 million passengers a year. At firstpeople were afraid to travel underground. This is what onenewspaper reader warned :To make approximately two miles of railway, 900 houses had to be destroyed. Thus the London tuberailway led to a massive displacement of the London poor, especially between the two world wars.Yet the Underground eventually became huge success. By the twentieth century, most large metropolisessuch as New York, Tokyo and Chicago could not do without their well functioning transit system.As a result, the population in the city became more dispersed. Better planned suburbs and good railwaynetwork enabled large number to live outside central London and travel to work.

Railway lines being laid in London, Illustrated Times, 1868.

Cows on the streets of London, The Graphic, 1877

SOCIAL CHANGE IN THE CITYTies between members of households loosened, and among the working class the institution of marriage

tended to break down. Women of the upper and middle classes in Britain, on the other hand, facedincreasingly higher levels of isolation, although their lives were made easier by domestic maids who

cooked, cleaned and cared for young children on low wages.Women who worked for wages had some control over their lives, particularly among the lower social

classes. However, many social reformers felt that the family as an institution had broken down, andneeded to be saved or reconstructed pushing these women back into the home.



1. Men, Women and Family in the City : Men and women did not have equal access to this new urban

space. As women lost their industrial jobs and conservative people railed against their presence inpublic spaces, women were forced to withdraw into their homes. The public space became increasinglya male preserve, and the domestic sphere was seen as the proper place for women. Most political

movements of the nineteenth century, such as Chartism (a movement demanding the vote for all adultmales) and the 10-hour movement (limiting hours of work in factories), mobilised large numbers of men.Only gradually did women come to participate in political movements for suffrage that demanded theright to vote for women, or for married women’s rights to property (from the 1870s).

By the twentieth century, the urban family had been transformed yet again, partly by the experienceof the valuable wartime work done by women, who were employed in large numbers to meet war

demands. The family now consisted of much smaller units.2. Leisure and Consumption : For wealthy Britishers, there had long been an annual ‘London Season’.

Several cultural events, such as the open the theatre and classical music performances were organised

for a elite group of 300-400 families in the late eighteenth century. Meanwhile, working classes met inpubs to have a drink, exchange news and sometimes also to organise for political action.Many new types of large-scale entertainment for the common people came into being, some madepossible with money from the state. Libraries, art galleries and museums were established in the

nineteenth century to provide people with a sense of history and pride in the achievements of theBritish. At first, visitors to the British Museum in London numbered just about 15,000 every year.

A famous London resort, painting by T.E. Turner, 1923

POLITICS IN THE CITYIn the severe winter of 1886, when outdoor work came to a standstill, the London poor exploded in a

riot, demanding relief from the terrible conditions of poverty. Alarmed shopkeepers closed down theirestablishements, fearing the 10,000 strong crowd that was marching from Deptford to London. Themarchers had to be dispersed by the police. A similar riot occurred in late 1887; this time, it was

brutally suppressed by the police in what came to be known as the Bloody Sunday of November 1887.Two years later, thousands of London’s dockworkers went on strike and marched through the city.According to one writer, ‘thousands of the strikers had marched through the city without a pocketbeing picked or window being broken....’ The 12-day strike was called to gain recognition for thedockworkers’ union.



THE CITY IN THE COLONIAL INDIAThe pace of urbanisation in India was slow under colonial rule. In the early twentieth century, no morethan 11 percent of Indians were living in cities. A large proportion of these urban dwellers wereresident of the three Presidency cities. These were multi-functional cities, they had major ports,warehouses, homes and offices, army camps, as well as educational institutions, museums and libraries.Bombay was the premier city of India. It expanded rapidly from the late nineteenth century,its population going up from 644,405 in 1872 to nearly 1,500,000 in 1941.

A bustling sreet in Null Bazaar, Bombay,photograph by Raja Deen Dayal, latenineteenth century.

1. Bombay the Prime city of India ? : Bombay was a group of seven islands under Portuguese control.In 1661, control of the islands passed into British hands after the marriage of Britain’s King Charles II tothe Portuguese princess. The East India Company quickly shifted its base from Surat, its principalwestern port, to Bombay.

Later in the nineteenth century, the city functioned a port through which large quantities of rawmaterials such as cotton and opium would pass. Gradually, it also became an important administrativecentre in western India, and then, by the end of the nineteenth century, a major industrial centre.

A view of Bombay, 1852.

2. Work in the City : The city quickly expanded. With the growth of trade in cotton and opium, largecommunities of traders and blankers as well as artisans and shopkeepers came to settle in Bombay.The establishment of textile mills led to fresh surge in migration.



The first cotton textile mill in Bombay was establish in 1854. By 1921, there were 85 cotton mills withabout 146,000 workers. Only about one-fourth of Bombay’s inhabitants between 1881 and 1931 wereborn in Bombay the rest came from outside. Large numbers flowed in from the nearby district ofRatnagiri to work in the Bombay mills.

Women formed as much as 23 per cent of the mill workforce in the period between 1919 and 1926.After that, their numbers dropped steadily to less than 10 per cent of the total workforce, By the late1930s, women’s jobs were increasingly taken over by machines or by men.

A map pf Bombay in the 1930sshowing the seven islands and the reclamations.

3. Housing and Neighbourings : Bombay was a crowded city. While every Londoner in the 1840senjoyed an average space of 155 square yards, Bombay had a mere 9.5 square yards. By 1872, whenLondon has a average of 8 persons per house, the density in Bombay was a high as 20. From its earliestdays. Bombay did not grow according to any plan, and houses, especially in the Fort area, were

interspersed with gardens. The Bombay First area which formed the heart of the city in the early 1800swas divided between a ‘native’ town, where most of the Indians lived, and European or ‘white’ section.

Many families could reside at a time in a tenement. The Census of 1901 reported that the mass of theisland’s population or 80 per cent of the total, resides in tenements of the one room; the averagenumber of occupants lies between 4 and 5 ....’ High rent forced workers to share homes, either withrelatives or caste fellows who were steaming into the city. People had to keep the windows of theirrooms closed even in humid weather due to the ‘close proximity of filthy guttes, privies, buffalo stablesetc.’ Yet though water was scarce, and people often quarrelled every morning for a turn at the tap,observers found that houses were kept quite clean.

The homes being small, streets and neighbourhoods were used for a variety of activities such ascooking, washing and sleeping. Liquor shops and akbaras came up in any empty spot. Streets werealso used for different types of leisure activities. Parvathibai Bhor recalled her childhood years in theearly twentieth century this way. ‘There was an open space in the middle of our four charts. There themagicians, monkey players or players or acrobats used to regularly perform their acts. The Nandi bullused to come. I used to be especially afraid of the Kadaklakshmi. To see that they had to beatthemselves on their naked bodies in order to fill their stomachs frigntened me’. Finally, chawls were alsothe place for the exchange of news about jobs-strikes riots or demonstrations.

Caste and family groups in the mill neighbouring were headed by someone who was similar to a villageheadman. Sometimes, the jobber in the mills could be the local neighbourhood leader.

He settled disputes, organised food supplies or arranged informal credit. He also brought importantinformation on political developments.



Chawl on Kalbadevi Road built in the early twentieth century.

4. Land Reclamation in Bombay : The need for additional commercial space in the mid-nineteenthcentury led to the formulation of several plans, both by government and private companies, for thereclamation of more land from the sea. Private companies became more interested in taking financialrisks. In 1864, the Back Bay Reclamation Company won the right to reclaim the western foreshore fromthe tip of Malabar Hill to the end of Colba. Reclamation often meant the levelling of the hills aroundBombay. By the 1870s, although most of the private companies closed down due to the mounting cost,the city had expanded to about 22 square miles. As the population continued to increase rapidly in theearly twentieth century, every bit of the available area was built over and new areas were reclaimed

from the sea.

5. Bombay as the City of Drams : The world of Cinema and culture : Many Bombay films deal with thearrival in the city of new migrants, and their encounters with the real pressures of daily life. Somepopular songs from the Bombay film industry speak of the contradictory aspects of the city. In the filmCID (1956) the hero’s buddy sings, ‘Ai dil hai muskil jeena yahan : zara hatke zara bachke ye haiBomaby meri Jaan’ (My heart, it is difficult to live here ! more over a little, take care of yourself this isBombay my love). A slightly more disillusioned voice sings in Guest house (1959); Jiska juta usika sar, dilhai choota bada shahar, ye hai tumahri Bombay; (Bombay, you city what a place ! Here one getsbeaten with one’s own shoes ! The city is big but people’s hearts are small).

Most of the people in the film industry were themselves migrant who came from cities like Lahore,Calcutta, Madras and contributed to the national character of the industry. Those who came from

Lahore, then in Punjab, were especially important for the development of the Hindi film industry. Manyfamous writers, like Ismat Chughtai and Saadat Hasan Manto, were associated with Hindi cinema.

CITIES AND THE CHALLENGES OF THE ENVIRONMENTThe widespread use of coal in homes and industries in nineteenth century. England raised seriousproblems. In industrial cities such as Leeds, Bradford and Manchester, hundreds of factory chimneysspewed black smoke into the skies. People joked that most inhabitants of these cities grew up believingthat the skies were grey and all vegetation was black ! Shopkeepers, homeowner and other complainedabout the black fog that discended on their towns, causing bad tempers, smoke-related illnesses,and dirty clothes.



When people first joined campaigns for cleaner air, the goal was to control the nuisance throughlegislation. This was not at all easy, since factory owners and stead engine owners did not want to

spend on technologies that would improve their machines. By the 1840s, a few towns such as Derby,Leeds and Manchester had laws to control smoke in the city. But smoke was not easy to monitor ormeasure, and owners go away with small adjustments to their machinery that did nothing to stop thesmoke. Moreover, the Somke Abatement Act of 1847 and 1853, as they were called, did not alwayswork to clear the air.

Calcutta had a long history of air pollution. Its inhabitants inhaled grey smoke, particularly in thewinter. Since the city was built on marshy land, the resulting fog combined with smoke to generatethick black smog. High levels of pollution were a consequence of the huge population that depended ondung and wood as fuel in their daily life. But the main polluters were the industries and establishmentsthat used steam engines run on coal.

IMPORTANT TERMS

1. Many decades after the beginning of the industrial revolution, most western countries were largelyrural till 1850.

2. More than three quarters of the adults living in Manchester were migrants from rurals areas till 1851.

3. One out of every nine people of England and Wales lived in London by 1750.

4. The population of London multiplied four fold between 1810-80.

5. The compulsory Elementary Education Act was passed in 1870.

6. The factory Acts beginning from 1902.

7. The responsibility for housing the working class was accepted by the British state in 1919-39.

8. ‘Charls Dickens wrote about the massive destruction in the process of construction in 1848.

9. The London poor exploded in riot demanding relief in 1886.

10. A similar riot occurred in late 1887.

11. One fifth of the streets of Paris were Haussmann’s creation by 1870.

12. Bankim Chandra Chattopadhyay wrote short sketches on urban life in Calcutta in 1962.

13. After the marriage of Britain’s King Charles II to the Portuguese princess the control of Bombay wastransferred to Britishers in 1661.

14. Bombay became the capital of Bombay Presidency in 1819.

15. About 1/4 of Bombay’s inhabitants were born in Bombay, the rest came from outside between 1881 and1931.

16. Bombay was built a dry dock between 1914-18.

17. The film industry employed 520,000 people by 1987.

18. Calcutta became the first city to get smoke nuisance legislation in 1863.

19. The smoke abatement Act of 1847 and 1853.



A. VERY SHORT ANSWER TYPE QUESTIONS

Q.1 What is metropolis ? Give an examples of

metropolis in India.

Q.2 Name two industrial cities in England in 19th

century.

Q.3 Mention two steps taken by the London

authorities to discipline its population.

Q.4 Why were the slams considered to be threat

to public for London ?

Q.5 Why were the slums considered to be threat

to public health ?

Q.6 Name two Acts passed in England to keep the

children out of industrial world.

Q.7 When by whom was the first movie made in

Bombay ? What did the movie depict ?

Q.8 Name the first proper Hindi movie. By whom &

when was this movie made ?

Q.9 Mention the problems raised in England in 19th

century due to widespread use of coal in

industrial cities.

Q.10 Which two stations of London were connected

by the first underground railways ?

Q.11 When was the Rent Act passed in Bombay ?

What was its out come ?

Q.12 Under what circumstances were the ancient

cities developed ?

Q.13 Name four industries which employed largest

member of people is London in early 20th

century ?

Q.14 What is meant by temperance movement ?

What was its main aim ?

Q.15 When was the Bombay Improvement Trust

established ? What was its immediate

achievement ?

Exercise - I UNSOLVED PROBLEMSB. SHORT ANSWER TYPE QUESTIONS

Q.1 Examine the historical processes involved in

the development of cities.

Q.2 Mention the steps taken to clean up London.

Q.3 Explain the evolution of Bombay as one of the

major cities of India.

Q.4 Describe the Bombay fort area.

Q.5 What is referred to as Chawls in Bombay ?

With which kind of London housing can these

be compared ? How are these similar ?

Q.6 Examine the effects of air pollution on Calcutta.

Q.7 By whom was the concept of a Garden city

first developed ? What were the main features

of the proposed Garden city ?

Q.8 Examine the difficulties faced by people due to

construction of underground railways.

Q.9 How was the family life transformed in an

industrial city of London ?

Q.10 What were the mode of entertainment in the

18th century England ?

Q.11 Examine the new types of large scale

entertainment for the common people

introduced in 19th century.

Q.12 Why was the expansion of the city of Bombay

difficult ? Mention any one way adopted to

develop the city.

Q.13 How does urbanisation pose a threat to

environment ?

Q.14 When did Bombay film industry make its first

appearance ?

Q.15 Why police was worried for the law and order

of London ?



Q.16 Mention various measures which were taken

to decongest London in the 19th and 20th

centuries. [Delhi 2009]

Q.17 How far was the underground railway able to

solve trasnport problems as well as housing

crisis in London in the nineteenth century?

[O.I. 2008]

Q.18 Why is Mumbai (Bombay) known as the city of

dreams? Give three reasons. [Delhi 2010]

C. LONG ANSWER TYPE QUESTIONS

Q.1 “London was powerful magnet for largest

population”. Explain.

Q.2 How were women employed in London beyond

19th century ? How did the situation change

after 20th century.

Q.3 What were the reasons for concern behind

providing housing for poor in London ?

Q.4 What were chartist movement and Ten Hour

Movement ?

Q.5 How do we distinguish between cities on the

one hand and towns and villages on the other?

Q.6 Explain the life style of workers of the

mid-nineteenth century in Britain. [A.I. 2010]

Q.7 How did the development of cities influence

the ecology and environment in late 19th

century? Explain by giving an example of

Calcutta. [Delhi 2011]

Q.8 Explain any three reasons for the increasing

concerns about the need for housing for the

poor in London after the Industrial Revolution.

[A.I. 2011]

Q.9 Describe in brief the development of Bombay

(Mumbai) as the 'Prime City' of India.

[A.I. 2012]

Q.10 How is urban development directly related to

the cost of ecology and environment? Explain,

giving examples of industrial cities of England

in the nineteenth century. [Delhi 2008]

Q.11 Explain any three reasons for which the

population of the London City expanded over

the nineteenth century. [O.I. 2009]

Q.12 Explain the social changes which led to the

need for the underground railways in London.

[A.I. 2007]

Q.13 What was the tradition of 'London Season'?

Explain different forms of entertainment that

came up in nineteenth century England to

provide leisure activities for the people.

[A.I. 2011]

Q.14 Describe the means of entertainment available

in England in the Nineteenth Century.

[RBSE 2013]



Q.1 What was not a reason for providing mass

housing schemes for the workers ?

(A) Concern for the poor

(B) Fear of Social disorder

(C) Threat to public health

(D) All the above

Q.2 Which movie did Dada Sahab Phalke make ?

(A) CID

(B) Guest house

(C) Raja Harishchandra

(D) Tezab

Q.3 Bombay was first under whose control ?

(A) Portuguese (B) English

(C) French (D) Dutch

Q.4 Which of the following is not a Presidency city?

(A) Madras (B) Bombay

(C) Calcutta (D) Lucknow

Q.5 Which of the following cities has developed

in a planned manner ?

(A) Delhi (B) Madras

(C) Signapore (D) Lucknow

Q.6 When was the first movie made in India ?

(A) 1886 (B) 1887

(C) 1888 (D) 1889

Q.7 When was the Rent Act passed in Bombay ?

(A) 1910 (B) 1918

(C) 1920 (D) 1922

Q.8 Who developed the concept of a Garden city?

(A) Ebenezer Howard

(B) Clive

(C) Pluto

(D) John Mill

Q.9 Name the Industrial city of England in 19th

century -

(A) London (B) Leeds

(C) Washington (D) None of these

Exercise - II NTSE/OLYMPIAD PROBLEMSQ.10 The city of Bombay improvement trust was

established in -

(A) 1996 (B) 1897

(C) 1898 (D) 1900

Q.11 The compulsory Elementary Education Act was

passed in -

(A) 1860 (B) 1870

(C) 1880 (D) 1890

Q.12 ................ became the first city to get smoke

nuisence legislation in 1863.

(A) Delhi (B) Bombay

(C) Jaipur (D) Calcutta

Q.13 Bombay was built a ............... between

1914-18

(A) Harbour (B) Capital

(C) Seaport (D) Dry dock

Q.14 The film industry employed .............. people

by 1987.

(A) 500000 (B) 520,000

(C) 540,000 (D) 560,000

Q.15 Bombay became the capital of Bombay

Presidency in -

(A) 1817 (B) 1818

(C) 1819 (D) 1820

Q.16 What is the meaning of urbanization?

(A) Development of a city or town

(B) People migrating from rural to urban

(C) Expansion of city

(D) All these

ANSWER KEY1. A 2. C 3. A 4. D

5. C 6. A 7. B 8. A

9. B 10. C 11. B 12. D

13. D 14. B 15. C 16. D

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