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M. Salman Khan
Chapter-3
Scalars & Vector
Q1. Differentiate between Scalars and Vectors.
Scalars VectorsPhysical Quantities which can be
completely specified by a number with a
suitable unit with out mention of
direction are known as Scalars.
Physical Quantities which can be
completely specified by a number with a
suitable unit and direction are called
Vectors.
Mass, Volume, Density, Temperature,
Energy, Electric Potential, Charge, Time
and Distance are the examples of Scalar
Quantities.
Acceleration, Force, Velocity,
Displacement, Momentum and Electric
Intensity are the examples of Vector
Quantities.
Scalars can be added, subtracted,
multiplied and divided by simple
arithmetical rules.
Vectors can be added, subtracted,
multiplied and divided by vector
algebra.
As the scalars are the simple numbers
therefore they do not have any special
representation like vectors.
A vector quantity is represented by an
arrow, length of the arrow is
proportional to magnitude of the vector
quantity, the direction of the arrow
represent the direction of vector
quantity.
Q2. Define the following :1. Head to Tail Rule
2. Negative of a vector
3. Null vector
4. Resultant vector
I. HEAD TO TAIL RULE To add two or mote vectors by this method they are drawn on a suitable scale such that the
head of one vector coincides with the tail of other and so no. The resultant vector is obtained by
joining the tail of the first vector to the head of the last vector. It is directed from the tail of the
first vector to the head of the last vector. It is directed from the tail of the first vector to the head
of the last vector. The magnitude and the direction of the resultant are found by using ruler and
protractor.
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II. NEGATIVE OF A VECTOR Suppose we have a vector A, then its negative is define as
A vector having the same magnitude as that of given “Vector A” but opposite in direction
is called the negative vector of A and is denoted by “-A”.
III. NULL VECTOR
It is a vector having zero magnitude and orbiting direction. It is denoted by O.
IV. RESULTANT VECTOR When two or more than two vectors are added we get a single vector which has the same
effect as the combined effect of all the vectors to be added. This single vector is known as
the resultant vector.
The resultant of A and B is R. symbolically we can write as
R = A + B
Q3. Write note on the following Subtraction of vectors.
SUBTRACTION OF VECTORSThe subtraction of two vectors is just like addition of vectors. In order to subtract a A from
B, the negative of A (i.e. -A) is added to B, and the resultant vector R of –A and B is found
which gives the difference between B and A.
Q4. Explain graphically method of addition of vectors.
GRAPHICAL METHOD OF VECTOR’S ADDITION Addition of Vectors:
The process of combining two or more vectors to produce a single vector
(called resultants) is known as addition.
Graphical Method of Vector’s Addition
In this method the magnitude and direction of a resultant vector is found by ruler and protractor.
We can explain the given procedure as follows
1. First we chose a system of reference
2. Draw the second vector with suitable scale keeping in view its magnitude and
direction.
3. Draw the second vector using the same scale by placing the tail of second vector on
the Head of the first vector.
4. Join the “head” of the second vector with the tail of the first vector. The straight line
joining the tail of the first vector to the head of the second vector represented the
“Resultant Vector”2
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When three of more vectors to be added two vectors are added first, then the next one and
so on. This procedure could be extended to any number of vectors involved. Symbolically
R = A + B + C ……………………
Q5. Define resolution of a vector. Describe a method of resolving a vector in to its
rectangular components.
RESOLUTION OF VECTORThe process of splitting up of a single vector into a number of vectors is called “Resolution of
Vectors”.
RECTANGULAR COMPONENTSThe components of a vectors which are at right angles to each other are called rectangular
components.
RESOLVING A VECTOR INTO ITS COMPONENTS
1. Consider a vector A which makes an angles “O” with the x-axis, the vector A is
drawn by placing its tail at the origin of rectangular co-ordinate system.
2. From the head of the vector A perpendicular lines are drawn to the axis and drawn to
the axis and Ax and Ay are so formed are regarded as the components of A, By
parallelogram law of vector addition.
A = Ax + Ay
Ax is acting along the x-axis
Ay is acting along the y-axis
MAGNITUDES OF Ax and AyFor Ay
Consider right angled triangle OPQ Perp / Hyp = Sin
or Ay / A = Sin
or Ay / = A Sin
or Ay = A Sin
For Ax
Base / Hyp = Cos
or Ax / A = Cos
or Ax = A Cos
or Ax = A Cos
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Q6. Explain addition of two vector perpendicular to each other. (Addition of rectangular
component method).
Suppose these are two forces F1 and F2 are acting on a body and making an angle of 90o
with each other. We have to find the resultant force.
In the above figure OA and AB represent F1and F2 respectively and OB is the resultant
vector of these forces. OAB is and right angled triangle and we can use Pythagoras Theorem.
Hence,
(OB)2 = (OA)2 + (OB)2
or R2 = F12 + F22
or R = F12 + F22
The direction of “R” can be calculated by using trigonometric ratios.
Tan = F2/ F1 (Tan = Perp./Base)
= tan-1 F2/F1
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Chapter-4
Kinematics
Q1. Define the following: Rest
Motion
Translatory Motion
Rotatory Motion
Vibratory Motion
Displacement
RESTA body is said to be at rest when it does not change its position with respect to its
surrounding objects.
EXAMPLE OF RESTExamples of position of Rest are given below.
1- A book lying on a table.
2- A bird sitting on a wall.
MOTIONA body is said to be in motion when it changes its position with respect to its surrounding objects.
EXAMPLES OF MOTION Examples of position of Motion are given below.
1- A book lying on a table.
2- A bird sitting on a wall.
TRANSLATORY MOTIONIt is the motion which is associated with bodies moving in a straight line, e.g.; The motion of a car
on a straight road, the flying of an aeroplane, the falling of brick etc.
VIBRATORY MOTIONTo and for motion of an object about a mean position is called vibratory motion or oscillatory
motion. Motion of a swing, motion of the string of sitar or violin are the examples of vibratory
motion.
ROTATORY MOTIONWhen a body moves such that its distance from a fixed point remains constant, its motion is
said to be rotatory motion.
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Motion of the wheel of cycle, hands of clock and wing of a fan are the examples of rotatory
motion.
DISPLACEMENTIt is a vector quantity which signified the least distance between two points in a particular
direction.
Q2. Write note on the following: Speed
Velocity
Uniform and Variable Velocity
Acceleration
Deceleration
Uniform Acceleration
Acceleration due to Gravity
SPEED“Rate of change of distance is called speed”. It is measured by the distance traveled by a
body in unit time. If covered distance denoted by “S” and time taken by “t” and speed by “v” then
Speed = Distance Covered / Time
or Vav = S/ t S.I unit of speed is meter/second
or m/s or ms-1
VELOCITY“Rate of change of displacement is called velocity”
or
“Speed of a body in specified direction is called velocity
The average velocity of a moving body is given by the displacement divided by the time elapsed.
Average Velocity = Displacement / Time Elapsed
or Vav = d / t
S.I. unit velocity is meter/second or ms-1
UNIFORM VELOCITYThe velocity of a body is said to be uniform if it covers equal distance in equal intervals of
time in a specified direction.
VARIABLE VELOCITYThe value of velocity may change due to a change in magnitude or change in direction or in both.
Thus a body is said to posses a variable velocity if its speed or its direction changes continuously.
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ACCELERATION“Rate of change of velocity is called acceleration”. The word change may imply an alteration in
direction or in magnitude or in both.
Suppose Vi is the initial velocity and Vf is the final velocity, then (Vf )
Change in velocity = Vf -Vi
If this change occurs in time “t” then
Rate of change of velocity = a = (Vf - Vi ) / t a = ( Vf - Vi ) / t
or aav = V / t
unit of acceleration m/s2 or ms-2
DECELERATIONIf the rate of change of velocity is negative then it called deceleration or retardation.
UNIFORM ACCELERATION If velocity changes uniformly in equal intervals of time, however short the interval may be, in a
straight line the acceleration so produced is called uniform acceleration.
ACCELERATION DUE TO GRAVITYAll bodies irrespective of their masses, while falling freely under gravity experience the same
acceleration called acceleration due to gravity. Average value of this acceleration is found to be 9.8
ms-2. It is denoted by “g”.
Q3. Drive the following Vf = Vi + at
S = Vit + ½ at2
2as = Vf2 - Vi
2
Answer :
S = Vit + ½ at2
PROOF :Suppose initial velocity of a body = Vi
Final velocity of a body = Vf
Average velocity Va = (Vi + Vf ) / 2
Distance covered by a body in time “t”
S = Vav x t (1)
From equation of motion Vf = Vi + at, Substituting the value of Vf in eq.1
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S = ( Vi + Vi + at ) / 2 x t
or S = ( 2Vi + at ) / 2 x t
or S = 2Vit + at2 / 2
or S = 2 Vit/2 + at2/ 2
S = Vit + ½ at2
2as = Vf2 - Vi
2
Suppose initial velocity of a body = Vi
Final Velocity of a body = Vf
Average Velocity = Vav = ( Vf + Vi )/2
Let the body moves with average velocity till the time “t” then covered distance
S = Vav x t (1)
Substituting the value of Vav in eq. (1)
S = ( Vf + Vi ) / 2 x t (2)
From equation of motion Vf = Vi + at,
Substituting the value of “t” in eq. (2)
S = ( Vf + Vi ) / 2 x ( Vf - Vi ) / a
S = (Vf ) 2 - (Vi) 2 /2a
or 2as = Vf 2 - Vi 2
2as = Vf 2 - Vi 2
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Chapter -6
Static
Q1. Write a note on “Torque”.
Definition:“The turning effect of a force about the axis of rotation is called torque or moment of that force”.
We can measure it by the product of force and moment arm.
Mathematical Representation:The torque is represented by a Greek letter Tau () symbolically
= F x r
where “r” is the moment arm.
Magnitude of torque = = F r Sin
or = Fr Sin
Where “” is angle between F and r.
UNITS OF TORQUEForce is measured in Newton and moment arm in meter, then unit of torque is “Newton
Meter” or “Nm”.
DIRECTION OF TORQUEThe direction of torque is always normal to the plane formed by F and r. The torque causing
anticlockwise rotation is regarded as a vector directed along the axis outward from the page.
Similarly torque causing clockwise rotation is regarded as vector directed along the axis into
the page and conventionally taken to be -ve.
MOMENT ARMThe perpendicular distance b/w the line of action of force and axis of rotation is called moment
arm.
FACTORS UPON WHICH THE TORQUE DEPENS Torque depends upon the following factors.
a) Magnitude of the force. Torque and magnitude of force are directly proportional to each other.
b) Magnitude of the moment arm. Torque and moment arm also directly proportional to each other.
POSITIVE TORQUEThe torque which tends to rotate a body in counter clockwise rotation is given a positive sign.
NEGATIVE TORQUE The torque which tens to rotate a body is clockwise rotation is given as negative.
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Counter Clockwise Rotation
is out of the paper.
is taken positive.
Clockwise Rotation
is into the paper.
is taken negative.
MINIMUM & MAXIMUM VALUES OF TORQUETorque is zero when
Moment arm is zero i.e. r = 0
Angle b/w F and r is zero i.e. = 0
= F r Sin = F r x 0 = 0
Torque is maximum when
Maximum force is applied
Maximum possible length of moment arm.
Angle b/w F and r is a right angle i.e. ( = 90o)
Q2.a) Define centre of gravity?
b) Find the centre of gravity of the fall Objects sphere, Uniform Road, Circular Plate, Plate
(Square, Rectangular, Parallelogram Shaped)
c) Explain how would you locate the centre of gravity of an irregular piece of metal shape?
a) CENTRE OF GRAVITY “The point inside or outside the body, where the whole weight of body appears to act is
called centre of gravity”.
b) CENTRE OF GRAVITY OF SOME OBJECTS
S.No. Name Of Object Position Of Centre Of Gravity
1. Sphere Centre Of Sphere
2. Uniform Rod Centre Of Rod
3. Circular Plate Centre Of Plate
4. Plate ( Square, Rect., or
Parallelogram in Shape
Interaction Of Diagonals
5. Triangular Plate Intersection Of Medians
6. Cylinder Mid Point Of Axis
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c) CENTRE OF GRAVITY OF AN IRREGULAR SHAPED BODY The centre of gravity of an irregular shape body cannot be found by simple geometrical
method, but a simple experiment can help to determine it.
To find the centre of gravity of an irregular shaped body drill a small hole “A” near the edge of
the cardboard.
Use this hole to hang the cardboard from a nail.
With the help of plumb line draw a line “Aa” on the cardboard.
Repeat this experiment using the holes “B” & “C” respectively, and draw Bb and Cc. These lines
intersect each other at a point “G”. The centre of gravity lies at their point of interaction “G”.
Q3.a) Define equilibrium
b) State the two conditions of equilibrium
c) Define the types of equilibrium.
d) Distinguish the three types of Equilibrium.
a) EQULIBRIUM When two or more than two forces act on a body simultaneously in such a manner that there is no
change, either in it’s translational motion on in it’s rotational motion, the body is said to be in
Equilibrium.
b) FIRST CONDITION OF EQULIBRIUMAccording to this condition if the resultant of all forces acting on a body is zero, the body is in
equilibrium.
i.e. F = O ( Sigma, stands for summation)
In general case, the forces are resolved into rectangular components i.e. x-components and y-
components. If forces are resolved into their components, then according to first condition.
If the sum of all forces acting along the x-axis is zero, the body is in equilibrium i.e. Fx = 0.
If the sum of all forces acting along the y-axis is zero, the body is in equilibrium i.e. Fy = 0.
If a body satisfies first condition of equilibrium, it’s translational acceleration is zero and the body is
said to be in Translational Equilibrium.
SECOND CONDITION OF EQULIBRIUMConsider a body which can rotate about a fixed point and there are some forces acting upon it,
then if the algebraic sum of all the torque on the body is zero, then it is in equilibrium.
If the second condition of equilibrium is satisfied then there is no angular acceleration and the
body is said to be in Rotational Equilibrium.
d) STATES OF EQULIBRIUM
STABLE EQULIBRIUM UNSTABLE
EQULIBRIUM
NEUTRAL
EQULIBRIUM
Centre of gravity of the Centre of Gravity of the Centre of Gravity of the
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body lies below the point
of support or suspension.
body lies above the point
of support or suspension.
body lies at point of
support or suspension
If we give a slight jerk, to
the body , the centre of
gravity rises.
If we give a slight jerk to
the body, the centre of
gravity of the body is
lowered.
If we give a slight jerk to
the body, it’s centre of
gravity neither rises nor
lowered.
If a book is lifted from one
edge and then allowed to
fall, it will come back to
it’s original position.
If a pencil standing
vertically is slightly
distributed from it’s
position, it will not come
back to it’s original
position.
If a ball is pushed slightly
to roll, it will neither come
back to it’s original
position nor it will gain a
new position.
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Chapter-5
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Force And Motion
Q1. Define the following:
Force, Inertia, Coefficient of friction unit of force (Newton)
FORCEForce is that agent which changes or tends to change the state of rest or of uniform velocity of a
body.
INERTIAThe property of matter by virtue of which a body is incapable of changing its state of rest or of
uniform motion along a straight line.
COEFFICIENT OF FRICTIONIt is the ratio between limiting friction and normal reaction. It is denoted by
= Limiting friction / Normal reaction
= F / R
Unit Of Force (Newton):
One Newton is that amount of force which is required to produce an acceleration of 1m/s2 in a
body of mass 1 Kg.
Q2.a) State Newton’s first law of motion.
b) Explain the law and give the definition of force.
c) Give at least two examples from the daily life which explain the Newton’s first law.
a) STATEMENT“Every body continues in the state of rest or of uniform motion in a straight line unless it is
compelled to change that state by an external force.”
b) THIS LAW CONSIST OF TWO PARTSThe first part state that “A body at rest will remain at rest unless it is compelled to change that
state by an external force”. It is very easy to understand, it is our common observation that a book
lying on a table will continue to remain there until we displace it, This means an external
force is needed to change the state of rest. The second part state that, “A body in motion in a
straight line with a uniform velocity until it is acted upon by an external force”. According to
second part,
If we roll a ball on the ground, with some velocity it some keep on rolling forever.
If a bullet is fired from a short gun, it should keep on moving forever.
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But common observation seems to contradict these statements, we know that a ball rolling on the
ground and a bullet fired from a gun, stop after some time actually
there are three forces which stops the motion of bodies, these forces are the force of friction, force
of gravity and air resistance. Rolling ball stops due to force of gravity and air resistance. Moving
bullet stops due to force of gravity, air resistance. This means that if we could get rid of all these
forces the bodies will continue moving in a straight line.
c) EXAMPLES 1. The fireman in a railway engine, Swiftly moves the coal rod near the furnace and suddenly
stop the rod, in this process the rod comes to rest suddenly and coal already in motion
continues to move in the same direction and falls into the furnace.
2. A boy riding a push bike along a level road does not comes to rest immediately when he stop
pedaling. The push bike continues to move forwards, but eventually it comes to rest as the
result of opposing action of the air resistance and road friction.
Q3. State Newton’s Third Law Of Motion and give at least three examples
from your daily life.
STATEMENT“If one body exert a force on the second body, the second body exert an equal but opposite
force on the first”.
OR
“To every action there is an equal and opposite reaction”.
MathematicallyF . action = - F. reaction
The minus sign indicates that the two forces are acting in opposite directions.
Examples The birds while flying, push the air downward with their wings (action). The air exert an equal
and opposite force on the birds in the upward direction (reaction).
The swimmer pushes the water in the backward direction with a certain force (action), water
pushes the man forwards with an equal and opposite force (reaction).
The blades of the helicopter revolve in horizontal direction and pushes the air downwards
(action). The air lifts the helicopter vertically upward (reaction).
Q4. Define Inertia and give at least two examples from your daily life.
INERTIA“The property of matter by virtue of which a body is incapable of changing its state of rest
or of uniform motion in a straight line on its own accord is describe as Inertia”.
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A passenger in a bus falls backward when the bus suddenly starts moving, when the bus
starts moving the lower portion of the body share the motion of the bus, where the upper portion
is still at rest. Due to this reason passenger falls backward when the bus start.
A passenger falls forward when the bus in motion suddenly stops. When the bus in motion
the passenger sharing the motion of the bus, when bus stop the lower portion of the bus comes to
rest. The upper portion of the body is in motion, hence he fall forward.
Q5. Differentiate b/w Mass and Weight
MASS WEIGHT
The quantity of matter in a body is
called mass.
Weight is the force with which earth
attracts a body towards its centre.
It is the property of a body which
determines the acceleration produce in it
under the influence of a gravitational
force i.e. a= F/m
It is the measurement of gravitational force
between earth and the body
i.e. W=mg
It is a non-directional quantity. It is a directional quantity, and always
directed towards centre of the earth.
The mass of a body remain constant
every where.
The value of weight is different at different
distances from the centre of the earth.
Mass can be determined by ordinary
balance.
Weight is often measured by a spring
balance.
6/5
Q6. State Newton’s second law of motion and prove that F = ma.
STATEMENTWhenever a net force acts on an object it produces an acceleration in its own direction which is
directly proportional to net force and inversely proportional to mass of the object.
ExplanationIt is our common observation that if there is no change in the mass of the object, acceleration will
increase with the increase of net force on the object mathematically we can write it as
a F (mass is constant)
Similarly if the applied force remains the same, there by increasing mass of the object the
acceleration will decrease, mathematically we can write it as
a 1 / m (for a constant force)
By combining the above two relations
a F/m
or a = k F/m
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If 1 N force is applied on an object of mass 1 kg which produces an acceleration of 1 m/s2, then by
substituting these values we get.
1 = k 1/1
or k = 1
Substituting the value of ‘k’ in e.g.
a = k F/m
or a = (1) F/m
a = F/m
F = ma
Q7. Define momentum and
a) Write its Mathematical Form
b) State law of conservation of momentum and give it mathematical form
MOMENTUMA physical quantity that decides how easy or difficult it will be to stop a moving body is known as
momentum of the body.
Mathematically it can be calculated by the product of mass and velocity.
So momentum = mass x velocity
If momentum is denoted by ‘P’ then
P = mV
UnitAs mass is measured in ‘kg’ and velocity in m/s, therefore unit of momentum is Kg m/s or Ns
STATEMENT OF LAW OF CONSERVATION OF MOMENTUMIn an isolated system total momentum before and after collision remains the same.
ExplanationConsider an isolated system in which two bodies ‘A’ and ‘B’ are moving with the velocities ‘U1’
and ‘U2’ respectively suppose ‘U1’ > ‘U2’ and both are moving in the same line and same direction.
Momentum of body A = m1u1
Momentum of body B = m2u2
Total momentum of the system = m1u1 + m2u2
Suppose after time t they collide with each other, and their velocities becomes ‘V1’and ‘V2’
After collision momentum of body A = m1v1momentum of body
B = m2v2
Total momentum of the system after collision = m1v1 = m2v2
According to law of conservation of momentum
Momentum before collision = Momentum after collision
So,
m1u1 + m2u2 = m1v1 + m2v2
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Q8.
a) Define friction, give its mathematical form
b) Define the following
Coefficient of friction
Rolling friction
c) Advantages and Disadvantages of friction,
d) Methods of reducing the friction.
a) FRICTIONWhen a body slides or rolls on a surface it experience a force in a direction opposite to its motion.
Which resist the motion of the body. This resisting force is called Force Of Friction.
ExplanationSuppose a body of weight ‘W’ placed on a surface is drag by Force ‘F’. It experiences a force in a
direction opposite to its motion, when we increase the amount of applied force the value of
frictional force also increases up to some extent . From the experiments its is proved that force of
friction has the ability to increase its value with the increase of applied force till reaches the
maximum value. Due to this strange nature, force of friction is called self adjusting force. The
maximum value of friction is called limiting friction. When the applied force is exceed from the
limiting friction the body starts sliding. Experiments show that the limiting friction is proportional
to weight of the body. i.e. f w
or w = R
Therefore f R where “R” is the normal reaction
f = R
Here “” is the coefficient of friction, and it is dimension less constant.
b) CO-EFFICIENT OF FRICTION Coefficient of friction is the ratio b/w limiting friction and normal reaction, i.e.
= f / R
It depends upon nature of the surface and as it is dimension less constant.
c) Rolling FrictionIf we rolled a heavy spherical ball on smooth surface, an opposing force which try to stop the
motion of rolling ball is called Rolling friction.
DISADVANTAGES OF FRICTION Wear and tear of the machinery is due to excessive friction.
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A large amount of power is wasted in over coming friction and the efficiency of machine
decreases considerably.
ADVANTAGES OF FRICTION Without friction between feet and ground it is not possible to walk.
In the absence of friction, the brakes of motor car can not work.
METHODS OF REDUCING THE FRICTIONFriction can be reduced by the following methods:
The various part of the machine which are moving over one another are properly lubricated.
In machine the sliding of various parts is usually replaced by rolling and its is done by casing
ball bearing.
Where sliding is unavoidable a thick layer of greasing material is used between the sliding
surfaces.
The front part of fast moving objects is cars and aeroplanes are made obliged to decrease air
friction.
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Chapter -6
CIRCULAR MOTION AND GRAVITATION
Q 1. Define centripetal acceleration and give its mathematical form and on what
factors it depends.
DefinitionWhen a body moves in a circle, its direction changes continuously due to which an
acceleration is produce which is directed towards the centre of the circle. This
acceleration is called centripetal acceleration.
MATHEMATICAL FORMCentripetal acceleration = ac = v2/r
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Where ‘V’ is the speed of the body and ‘r’ is the radius of circle in which body
is moving.
Q2. a) Define Centripetal force.
b) Derive Fc =m2/r
c) On what factors Centripetal force depends.
d) Give some examples of Centripetal force from your daily life.
a) DefinitionWhen a body moves in a circle with uniform speed, the force required to keep it moving in
a circular path is called Centripetal force. This force is always directed towards the centre of the
circle.
b) MATHEMATICAL FORMSuppose a body of mass ‘m’ is moving in a circular path of radius ‘r’ with a
speed of “V m/s”.
According to Newton’s second law of motion
F = ma
or Fc = m ac
As we know that ac = v2/r
therefore Fc = mv2/r
Hence
Centripetal force Fc = mv2/r
c) FACTORS UPON WHICH CENTRIPETAL FORCE DEPENDSCentripetal force depends upon the following factor
Mass of the object Fc m Centripetal force is increases with the increase of mass of the
body and decreases by decreasing mass of the body.
Velocity of the object Fc x v2 Centripetal force is directly proportional to square of
the velocity. It increases with the increase of velocity.
Radius of circular path Fc x 1/r If radius of the circle in which body is moving increase,
Centripetal force will decrease.
EXAMPLES OF CENTRIPETAL FORCE FROM DAILY LIFE When a car moves along a round track, the force of friction between tyres and road provide
necessary centripetal force and keep the car on the curved path.
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Gravitational force between moon and earth provide centripetal force and keep the moon on a
circular path.
Q 3. Define centrifugal force and give some examples of centrifugal force from the
daily life.
CENTRIFUGAL FORCE Such a force which is produced by virtue of centripetal force is called centrifugal force.
It is a force of reaction of centripetal force. In case of motion of a stone whirled
in a circle, centripetal force acts on the stone and centrifugal force act on the hand.
MATHEMATICAL FORM As centrifugal force is the force of reaction, therefore its mathematical
representation is same as centripetal force but with negative sign.
Centrifugal force = - mv2/r
EXAMPLES FROM DAILY LIFE When we whirl a stone tied at the end of a string, we experiences an outward force on our
hand. This is centrifugal force.
Centrifuge system helps in separating honey from bees wax.
Q 4. State Newton’s law of gravitation and prove that F = G m1m2/d2.
STATEMENTEverybody in this universe l attracts every other body with a force which is directly
proportional to the product of their masses and inversely proportional to the square of the
distance between their centers.
MATHEMATICAL REPRESENTATIONSuppose two bodies A and B of masses ‘m1’ and ‘m2’ respectively and ‘d’ is
the distance between their centres.
As force of attraction between the bodies is directly proportional to product of their
masses, i.e. F m1 m2 -------- 1
This force is inversely proportional to square of the distance between their centres,
i.e. F 1/d2------- 2
Combining the relations 1and 2 we got
F = G x m1 m2 /d2
OR F = G m1 m2 /d2
When G is the gravitational constant.
Its value is G = 6.67x 10-11 N m2/kg2
Q 4. Derive an equation for mass of the earth, by applying law of gravitation.20
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Consider a body of mass ‘m’ place on the surface of the earth.
Suppose mass of the earth is Me then the force of attraction between the body and
earth is given by gravitational law
F = G m Me / Re2 -- 1
(Neglecting the distance between centre of the body and earth’s surface).
But we know that the force with witch earth attracts a body towards its centre is
weight i.e. F = W = mg ---- 2
By comparing 1 and 2 we get
mg = G m Me / Re2
or mg Re2 /Gm = Me
or gRe2/G = Me
or Me = gRe2 /G
With the help of above relation we can calculate the value of mass of the earth..
Q5. Calculate Mass of the earth.
With the help of gravitational law, we have derived a relation for mass of the earth,
i.e. Me = Re2g / G
We know that in S.I. Units Re = 6.4x106 m
g = 9.8 m/s2
G = 6.67x10-11 N m2/kg2
Substituting the values , we got
Me = (6.4x106)2 x 9.8 / 6.67 x 10-11
Me = 40.96 x 1012 x9.8 / 6.67 x 10-11
= 401.40 x 1012 + 11 / 6.67
= 60.1 x 1023
= 6.01 x 1024
Me = 6 x 1024 kg
Q6. Differentiate between g and G.
g GIt is the acceleration due to gravity It is gravitational constant
In S.I. units its value is 9.8 m/ s2 In S.I. units its value is 6.67 x 10-11 Nm2 /
Kg2
Its value increases by decreasing altitude
and vice versa
Its value is constant for whole universe
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Q7. Explain the variation of “g” with altitude.Value of “g” is not a constant gravity, its value depends upon the distance of the body from the centre
of the earth. The value of “g” varies inversly as the square of this distance, i.e.
g 1 / r2
Where “r” is the distance b/w centre of considering body and centre of the earth.
Therefore, at the earth, value of “g” is less at equator then pole because equatorial distance is more at
poles.
Differentiate b/w centripetal and centrifugal forces.
CENTRIPETAL FORCE CENTIFUGAL FORCE
It is a centre seeking force. It is centre fleeing force.
This force acts on the body making
circular motion
This force acts on the body providing
centripetal force
This force is a force of action This force is a force of reaction
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Chapter-8
WORK ENERGY & POWER
Q1.a) Define work and it’s units?
b) Evaluate work when force and displacement are not in one direction?
a) WORK Work is said to be done when a force “F” causes a displacement “d” in the body on which it
acts.
EXPLANATIONIf the displacement of the body takes place under the action of a constant force in the
direction of force, the work done is given by the product of the magnitude of force and that of the
displacement.
MATHEMATICAL FORMWork = ( Force ) ( Displacement )
or W = F S
UNITS OF WORKJOULE:
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In S.I units, the unit of work is Joule. It is defined as “the work done by a force of one
Newton in moving a body through a distance of one meter in the direction of force.
ERG:
In C.G.S. system the unit of work is ERG. It is defined as “the work done by a force of one
dyne while moving a body through a distance of one centimeter in the direction of force”.
FOOT POUND:
In British Engineering system the unit of work is Foot Pound. It is defined as “the work
done when a force of one pound moves a body through a distance of foot in a direction of force.
EVALUATE WORK WHEN FORCE AND DISPLACEMENT ARE NOT IN ONE
DIRECTIONIf force makes an angle with the direction of displacement then we calculate work by resolving
force into two components “Fx”, which acts along the direction of displacement “Fy”, which acts
perpendicular to the ground .
then, Fx = F Cos
Fy = F Sin
As the body is moving along the horizontal direction therefore the component Fx is doing
work, whereas the component Fy is not effective because no work is done along this direction
therefore.
Work = ( Fx ) (d)
or Work = (F Cos ) (d)
or Work = F d Cos
FACTORS ON WHICH WORK DEPENDS Displacement ( d )
Angle Between Force And Displacement
Q2. Define Potential Energy, Derive a formula of Potential Energy?
POTENTIAL ENERGYPotential Energy of a body is define as the energy due to position of a body.
Gravitational Potential EnergyIf a body is lifted to a position higher than it’s initial position in the gravitational field of
the earth, the work is done on it. This work is stored in this body as
potential energy. Such potential energy is called Gravitational Potential Energy. This energy is
recovered if the body is allowed to fall..
Magnitude Of P.E:
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Suppose a body of mass ‘m’ is situated at some point in a gravitational field of the earth. It
is lifted with very small speed vertically through a distance ‘h’. The force required to raise the
body is just equal and opposite to its weight (W=mg) of the body.
This work done on the body is, therefore, given by
Work = Force x Displacement
Work = W x h
Work = mgh
This work is equal to potential energy
P.E = mgh
Factors On Which Potential Energy DependsPotential energy depends upon the following factors.
Mass of the body
Height from initial point.
Value of acceleration due to gravity
Potential Energy is directly proportional to mass and height .
Q3. Define Kinetic Energy and derive the formula K.E =1/2 mv2 .
DEFINITION Energy possessed by a body by virtue of its motion is called the Kinetic Energy.
EXPLANATION It is the energy possessed by a moving body. A moving body is capable of doing work. The
work which a moving body can do is equal to its Kinetic Energy..
This energy has many practical application.
1) Generation of electricity from moving water is used to drive turbines.
2) Wind mills.
MAGNITUDE OF KINETIC ENERGYSuppose a body of mass “m” placed on a horizontal friction less table. Suppose force “F” is
applied on the body which accelerates the body in the direction of force, then according to
Newton’s Second law of motion, applied force
F = ma
Suppose the body starts its motion from rest and after covering “S” its final velocity
becomes “V”.
Using the equation of motion 2aS = Vf2 – Vi
2
Substituting the values, we get
2aS = V2 - 02
2aS = V2
S = V2 / 2a
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Work Done by the force
W= F x S
Or W= (ma) (V2 / 2a)
W= mv2 / 2
This work is appeared in the form of Kinetic Energy
Therefore K.E. =1/2 mv2
FACTORS ON WHICH K.E. DEPENDSKinetic Energy depends upon two factors.
1) MASS OF THE BODY
2) VELOCITY OF THE BODY
Kinetic Energy is directly proportional to mass of the body.
Kinetic Energy is directly proportional to square of the velocity.
Q: State the law of conservation of energy and explain this law for a freely
falling body.
LAW OF CONSERVATION OF ENERGY“Energy can neither be created nor it can be destroyed but it can changed from one form of energy to
another form of energy”.
EXPLANATIONConsider a body of mass ‘m’ lying at a height ‘h’ from the ground. When we release this body it will move
towards the ground and its potential energy decreases but Kinetic energy increases at the same time.
During this motion from A to C its potential energy changes into K.E. we will calculate P.E and K.E
at different points and total energy.
AT POINT A:K.E = 0 (body is at rest therefore, its velocity = 0)
P.E = mgh
Total Energy = P.E. + K.E.
= mgh + 0 = mgh
Total energy = P.E + K.E.
= mgh + 0 = mgh
AT POINT C:Distance covered by the body from A to C = x
Height from the ground = h-x
P.E at C = mg (h-x)
Initial velocity at A = vi =0
Final velocity at C = vf = v
By using the equation of motion.
2gh = Vf2 -Vi
2
2gx = V2 -(0)2
2gx = V2
K.E at C = ½ m V2
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= mgx
Hence total energy at C = E = P.E + K.E
E = mg (h-x) + mgx
E = mgh - mgx + mgx
E = mgh.
AT POINT B:P.E = 0 (h =0)
K.E = mgh
E = mgh + 0
E = mgh
During the motion from A to B potential energy is converted into Kinetic energy and Kinetic
energy is converted into potential energy, but total energy remains the same.
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Chapter-9
MACHINEQ1. Define the following.
Effort
Load
Mechanical advantage
Out put
Input
Efficiency.
EFFORT ‘P’It is a force directly applied to a machine for ding work. It is denoted by ‘P’.
LOAD ‘W’ The weight lifted or resistance overcome by a machine is known as weight and it is denoted by
‘W’.
MECHANICAL ADVANTAGEIf a weight ‘W’ is raised by a machine when an effort ‘P’ is applied, the ratio of load and effort is
called mechanical advantage of the machine, Hence
Mechanical Advantage = Weight or resistance overcome by a machine
Force applied on machine
M.A. = W P
INPUT If an effort ‘P’ acts through a distance ‘d’ then work done on machine is called Input, Thus
Input = effort x distance through which the effort acts.
Input = Pd
OUT PUTIf a machine moves a load ‘W’ through a distance ‘h’ then useful work done by machine is called out
put, thus
Out put = Load x distance through which the load moves
Out put = Wh
EFFICIENCY27
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The ratio between useful work done by the machine to the work done on the machine is called the
efficiency of the machine.
It is denoted by a Greek letter ‘’ (eta).
Efficiency = = useful work done by the machine
useful work done on the machine
Efficiency always expressed in percentage.
= Output x 100
Input
or = W x h x100
p x d
Q2.
Define lever.
On what principle it works.
Calculate its mechanical advantage.
Write down the types with some example.
a) DEFINITION :Lever is a straight rigid ban which can rotate about a fixed point. This point is called
Fulcrum.
b) ON WHAT PRINCIPE LEVER WORKSLever works on principle of moment i.e.
Moment of effort = moment of weight
OR effort x effort arm = weight x weight arm
c) MECHANICAL ADVANTAGEAs a lever works on principle of moment, therefore we can calculate the mechanical
advantage with the help of this principle i.e.
effort x effort arm = Weight x Weight
OR P X OA = W X OB
OR OA / OB = W / P
OR M.A. = W/P = OA / OB
M.A. = Effort Arm / Word Arm
Mechanical advantage of lever can be increased by increasing effort arm or by decreasing load arm,
to a minimum possible limit.
d) TYPES OF LEVER Lever is divided into three classes depending on different positions of fulcr relative to the point of
application of the force and resistance or weight.
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1. Lever Of The First Kind
In the lever of the first kind, fulcrum ‘F’ is in between effort ‘P’ and weight ‘W’.
Examples: Common balance, pair of scissors, Sea-Saw are the examples of the first kind of
lever.
2. Lever Of The Second Kind
In the lever of the second kind, weight ‘W” is in between Fulcrum ‘F’ and effort ‘P’.
Examples: Wheel barrow, nut crackers are the examples of second kind.
3. Lever Of Third Kind
In the third kind of lever, effort ‘P’ is in between weight ‘W’ and fulcrum ‘F’
Examples: Human arm and fire tongue are its examples.
Q: Write note on the following.
Pulley
Inclined plane
Wedge
Screw Jack
Wheel and axle.
PULLEYConstruction :
It consist of a grooved wheel which can carry a string, rope or chain passing round it.
The wheel mounted on an axle which is fixed to a frame work called Block.
The pulley used in two ways.
Fixed pulley
Moveable pulley
Fixed Pulley
If the block of the pulley is fixed it is called fixed pulley.
Working:
Load is attached at one end and effort is applied on the other end in downward direction to lift the
load.
Mechanical Advantage:If we ignore the weight of the rope and force of friction between the rope and wheel then from
principle of lever.
Effort x Effort arm = Weight x Weight arm
P x OA = W x OB
OA / OB = W / P
MA =W / P = OA / OB = r / r (where ‘r’ is the radius of wheel)
M.A. = 1
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Such pulleys used to change the direction of force. The advantage of fixed pulley is the force can
be applied in downward direction, which is more convenient.
Moveable pulleyArrangement And Working:
In this pulley, one end of the rope which is passing round the pulley is tied to a firm support ‘O’
and effort ‘P’ is applied at its other end. The load ‘W’ to be lifted, is hung from the hook of the block.
Mechanical Advantage:In each segment of the rope tension is equal to applied effort. As the weight is supported by the
two segments of the rope, the upward effort acting on weight ‘W’ is ‘2P’.
For equilibrium condition position.
W = 2P OR W/P = 2 OR MA = 2
INCLINED PLANE
Definition Inclined plane is a plane surface making a certain angle with the horizontal.
Use: It is used up to help us in raising heavy loads.
Mechanical Advantage:
Suppose AB is an inclined plane having length ‘l’’ height ‘h’ and the angle of inclination is
.
Suppose weight ‘W’ is being pulled up by a force ‘P’ parallel to plane surface. As
the weight ‘W’ is acting vertically downward, therefore it is resolved into its components.
W Cos which is balanced by normal reaction R.
W Sin which tend to pull the body parallel to plane surface. The force ‘P’ acting against
this force. If force of friction is neglected then for an equilibrium.
W Sin = P
OR W / P = 1/Sin ---- (1)
IN ABC,
Sin = h / l
Substituting this value in (1)
W / P = 1
h / l
OR M.A. = l / h
OR M.A. = length of inclined plane
height of inclined plane
M.A. of inclined plane can be increased by increasing length or by decreasing
height of inclined plane.
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WEDGE:DefinitionWedge is a simple machine made up of two inclined planes.Use.
Used as fulcrum in levers.
Used to split wood into small pieces.
Mechanical Advantage
Suppose a wedge is penetrated into a wooden log by a force ‘P’ . R1, R2 are two
reacting forces acting normally on the inclined planes.,
Consider the equilibrium position of Wedge and neglecting the frictional force.
R1, R2 and ‘P’ forms a triangle XYZ. Such that XY, YZ and XZ show P,
R1 and R2 respectively. As ABC and XYZ are two similar triangles therefore
ZX / XY = AC/BC (Ratio of the sides of similar triangles are equal)
OR R/P =AC/BC (ZX =R, XY =P) (R1 =R2 =R)
We know that
M.A. = Weight or resistance /Effort.
Is M.A. = R/P = length of inclined plane / Thickness of Wedge
CONCLUSIONM.A. of a wedge can be increased by increasing length of inclined plane and by
decreasing thickness of wedge.
SCREW
DefinitionScrew is a simple machine consists of a threaded rod with a circular head, called screw head.
UseIt is used to hold different parts of machines together.
Construction
It consist of two main parts.
A cylinder on which continuous threads are wrapped/
A circular grooved head on the top of a screw.
The distance b/w two consecutive threads is called pitch, and it is denote by “h”.
WorkingWhen an effort “P” is applied on the head of the screw, It completes one revolution and
moves through a distance equal to pitch of the screw.
Mechanical Advantage
When the screw completes one revolution, the effort “P” is applied for one
complete revolution and covered a distance equal to circumference of the circular head i.e. 2r
Where ‘r’ is radius of circular head; so the Input = P x 2r .
Where the screw moves for wand, It may be used to raise weights or over come
resistance applied to its ends a distance equal to pitch of the screw.
Therefore out put = W x h
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For an ideal condition,
Out put = Input
W x h = Px2r
W/P = 2r/h
Or MA = 2r/h
Hence MA can be increased by increasing radius of circular head or by decreasing
pitch of the screw.
Screw JackA Screw Jack is a simple machine usually used to lift car or other heavy automobile
when need arise.
ConstructionIt consist of a long Screw rod passing through a threaded block ‘B’ and a handle it
to turn the threaded block ‘B’.
WorkingWhen the effort is applied to the handle ‘H’ and the handle covers a distance equal to
circumference of the circle of radius ‘r’ where ‘r’ is equal to length of the handle. Due to this
effort the block moves equal to pitch of the screw and raised a load ‘W’.
Mechanical Advantage
For an ideal Screw Jack
Input = out put
P x 2r = W h
Or W/P = 2r / h
For a large mechanical advantage pitch of the screw should be small as compared to length
of the rod.
Wheel and AxleIt is a very simple machine used for lifting heavy loads, such as pulling bucket of water
from well.
ConstructionIt consist of two wheels, one is large having radius ‘R’ and the other wheel is small
having radius ‘r’. Both the wheels are fixed on the same shaft and are called wheel and axle.
WorkingThe effort is applied on the rim of the wheel and load is raised by a string wound round the
axle.
If effort ‘P’ is applied for one complete rotation of larger wheel having radius equal to ‘R’
then Input = P x 2R
Load is raised through a distance equal to circumference of axle, then Output = W x 2r
For an ideal condition
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Input = Out put
P x 2R = W x 2 r
Or W/P = 2R / 2r
Or W/P = R/r
M.A = R/r
M.A of wheel and axle is increased by increasing R or by decreasing r.
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Chapter-16
REFRACTION OF LIGHTQ1. Define refraction of light and state the laws of refraction?
REFRACTION:Refraction is the bending of light which occurs when it passes from one transparent medium
(material) to another.
i = angle of incidence. (angle b/w incident ray and normal)
r = angle of refraction (angle b/w refracted ray and normal)
e = angle of emergence (angle b/w emergent ray and normal)
LAWS OF REFRACTION:
First Law :
The incident ray, refracted ray and the normal at the point of incidence all lie in the same plane.
Angle of Deviation :
The angle with which incident ray deviates from its original path is called Angle of Deviation.Angle of Minimum Deviation :
The last value of angle of deviation after which it increases with the increase of angle of incidence is called Angle of Minimum Deviation.Second Law :
For light rays passing from one transparent medium to another, the sine of angle of incidence and
the sine of angle of refraction are in constant ratio. This constant is known as ‘Refractive Index’
and denoted by a Greek Symbol ‘’.
Mathematically = Sin i / Sin r
i = 20o Sin < i = 0.34 ‘n’ = Sin i / Sin r = 1.5
r = 13o Sin < r = 0.22
i = 30o Sin < i = 0.50 ‘n’ = Sin i / Sin r = 1.5
r = 19o Sin < r = 0.33
i = 40o Sin < i = 0.64 ‘n’ = Sin i / Sin r = 1.5
r = 25o Sin < r = 0.42
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Q2. Define refractive Index ? Describe different methods by which you can
calculate the refractive index of a medium ?
REFRACTIVE INDEX:It is the bending ability of a light ray in the second medium with respect to first, and it is different
in different medium. It is denoted by Greek symbol ‘n’.
Refractive index can be calculated by following different methods.
Refractive index is the ratio between sine of angle of incidence to sine of angle of refraction
Mathematically ‘n’ Sin i / Sin r
Refractive index can be calculate by dividing the speed of light in air to speed of light in second
medium
If V1 = Speed of light in air.
V2 = Speed of light in second medium (sup glass)
Then Refractive Index = ‘n’ = Sin i / Sin r
The refractive index of glass by prism can be calculated by the formula.
n = Sin (A+Dm) / 2
Sin A / 2
Where ‘A ‘ is the angle of prism.
‘Dm’ is the angle of minimum deviation.
The refractive index of a medium can be calculated by the formula n = 1/Sin C
Where ’C’ is the critical angle of that medium.
Q3) Define critical angle.
Define total internal reflection.
Explain the phenomena of total internal reflection?
Find a relation between the critical angle and the refractive index of the medium?
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CRITICAL ANGLE:
We know that when a ray of light passes from a denser medium to a rarer medium , the
refracted ray bends away from the normal. If now the angle of incidence “i” is slowly increased
the angle of refraction becomes 90o, then the refracted ray grazes along the boundary of the
media. This particular angle of incidence for which the angle of refraction become 90o is called
critical angle.
TOTAL INTERNAL REFLECTION:
When light passes from a denser medium to rarer medium it bends away from the normal
and having a small angle of incidence “i” and a weak internally reflected ray is produced as well
as a refracted ray . The angle of refraction is greater than the angle of incidence “i”. It follows that
if the angle of incidence is increased it will reach the critical value where the angle of refraction is
equal to 90o.
If the angle of incidence is further increased, become grater than the critical angle (i > c) it is
impossible for the angle of refraction to exceed 90o. Now no light emerges and the light is totally
internally reflected, The inside surface of denser medium behaves like a perfect mirror. This
phenomena is known as Total Internal Reflection.
Conditions For Total Internal Reflection:There are two conditions for total internal reflection.
The ray of light should incident from a denser medium to a rarer medium.
The angle of incidence should be greater than the critical angle.
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Q5. Write note on the following: Total reflecting prism.
Periscope.
TOTALLY REFLECTING PRISM:
A prism with one 90o corner and two 45o corners can be used to turn a ray of light through
90o. In fig. ray PQ is totally internally reflected, because the angle of incidence “i” = 45o is greater
than the critical angle for glass to air, angle C=42. The ray is deviated by 90o.
Use:
Totally reflecting prism is used in some periscope in preference to a plane mirror because there is
no exposed silvered surface to become damaged and no multiple reflections.
PERISCOPE:Introduction:
It is an optical instrument which is used to see the objects on the surface of the sea by an observer
in a submarine under water.
Construction:
It consist of two right angled triangle prism and three convex lenses. The first is fixed at the top
and the second prism P2 is fixed at the bottom of a vertical tube which bent at right angle at the
lower end. There is also a lens system in the tube.
Working:
The rays from the distant objects are reflected at right angles by the upper prism into the vertical
tube. The rays pass through a system of lenses and fall on the second prism P2. This prism bends
rays again and the rays then fall on an eye piece that forms a final enlarged image which can be
viewed by the observer.
Q6. Explain in detail the refraction of light through prism ?
INTRODUCTION:Prism is a transparent refracting medium bounded by two triangular and three rectangular
surfaces. Triangular section of the prism is called
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“Principle Section”. The angles of the triangle is called “Angle Of the Prism”.
Let PQ is the ray incident on the face “AB” of the prism at “Q”, refraction at Q takes place from
air to glass , the refracted ray QR bends towards the normal, when QR
reaches “R” refraction takes place again from glass to air, So the refracted ray bends away from
the normal “OM” at “R”. This ray is called a emergent ray.
Here refraction takes place two times, firstly when light ray enter into the prism, secondly when
light travel from glass to air.
Q8. Describe the changes in the position, nature and size of the image formed by convex lens
when the object is brought from infinity to optical centre of the lens. Draw the ray
diagram?
Case I : When An Object Placed At Infinity:
When an object is at infinity, the image is formed at principal focus. It is real, inverted and
extremely diminished.
Case II : When An Object Placed Beyond “2F” :
When an object is beyond “2F”, the image is formed between principal focus and “2F”. It is real,
inverted and smaller in size.
Case III : When An Object Placed At “2F” :
When an object placed at “2F” the image is formed at “2F”. This image will be real, inverted and
same in size.
Case IV : When An Object Placed b/w “F” and “2F” :
When an object placed b/w “F” and “2F”. This image will be real, inverted and magnified.
Case V: When An Object Placed At “F” :When an object is placed at “F” it’s image will be formed at infinity. This image will be real,
inverted and highly magnified.
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Case VI : When An Object With In The Focal Length:
When an object is placed within the focal length, it’s image is formed on the same side of the
object. This image is erect, virtual and magnified.
Q9: Draw a labelled diagram showing the structure of eye. Explain the functions of different
parts of the eye?
SCLEROTIC:It is the opaque coating of the eye.
CORNEA: The front portion of the sclerotic is slightly more convex than the rest of the eye ball, and is called
the Cornea.
CHOROID:
Inside the sclerotic is a blank opaque membrane called Choroid.
IRIS:
The front portion is a coloured diaphragm, called the iris.
PUPIL OF THE EYE: The iris contains a central aperture called the Pupil Of The Eye.
RETINA:The third coating inside the eye is called Retina.
OPTIC NERVES:This nerve carries the impression to the brain where it is translated into the mysterious
phenomena called “sight”.
LENS OF THE EYE:It is a convex lens, made of hard transparent gelatinous water.
AQUEOUS HUMOR:It is transparent matter filled b/w cornea and lens.
VITROUS HUMOR:It is highly transparent matter filled b/w lens and rating.
CILLARY MUSCLES:These muscles perform an important role. These muscles control the lens in
adjustment for seeing far off or a near by objects.
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Functions Of Parts Of Eye:SCLEROTIC:
It is hard coating to protect the eye
CHOROID:
It is a layer of tissue which supplies blood to the eye and also contains black colouring which
reduces reflection of light with in the eye.
RETINA:
It contains light sensitive cello and nerves fibres. Light falling on the retina produces chemical
changes in the cells which then send electrical impulses along the nerve fibres via optic nerve to
the brain.
LENS:
The lens forms a real, inverted and diminished image on the retina.
CILIARY MUSCLES:
It controls the shape of the lens. These muscles contract or relax so the thickness of the lens
changes
IRIS:
The iris is a coloured ring, which has a circular hole in it’s centre called the pupil, By adjusting
the size of the pupil, the iris can control the amount of light reaching the retina.
AQUEOUS AND VITREOUS HUMOR:
The eye is roughly spherical and keeps it’s shape due to liquid inside it called Aqueous And
Vitreous Humour.
Q10. What are the main defects of the eye? How are they removed? Following are the main
defects of the eye Short-Sightedness or Mypia
Long Sightedness or Hypermetropia
Astigmatism
Presbypia
Short-Sightedness Or Myopia:If a person cannot see distant objects but can see near objects, he is suffering from disease called
short sightedness.
Cause :In this case the eye ball of the person is too converging or the eye ball is too long as a result
of the image of distant objects is formed in front of the rating.
Removal:
This defect of the eye is corrected by using a concave lens of suitable focal.
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Long Sightedness:If a person cannot see near objects, but can see clearly the distant objects, he is said to be suffering
from long sightedness.
Cause:
In this case the eye ball of the person in less converging or the eye-ball is too short. For such a
person the rays from near objects are focussed beyond the retina.
Removal:
In order to bring the image at the retina a convex lens of suitable focal length is used which is in
front of the eye.
Q11. Write a note on Compound Microscope ?
COMPOUND MICROSCOPE:It is an optical instrument by which a small object can be seen very much large.
Construction:
It consists of two convex lenses of short focal length at one end of two tubes, one of these tubes can
be moved into the other, so that the distance between the lenses can be changed. The lens near the
object is called objective and the other near the eye is called Eye-Piece.
Objective:
This lens faces the object; it has short focal length or high power or small aperture.
Eye Piece:This lens faces the eye-piece. It has large focal length as compared to objective. It has large
aperture.
Working:The small object AB is viewed is placed in front of the objective at a distance slightly greater than
the focal length of the objective “O”, So that a real, inverted and enlarged image A’ B’ is formed.
The eye-piece is moved forward or backwards. So that A’ B’ falls within the focal length and final 41
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image A” B” is formed by the lens (eye- piece) at a distance of least district vision. A” B” is
inverted, virtual and magnified image of AB.
Q12. What do you know about magnifying glass Describe the function of magnifying glass?
MAGNIFYING GLASS OR SIMPLE MICROSCOPE:
When a convex lens is placed near a small object such that the distance between the lens and the
object is less than its focal length, a magnified erect and virtual image of the object is seen through
the convex, which is said to act as a simple microscope or magnifying glass.
Consider an object AB placed in front of a convex lens within the focal length. A ray which is
parallel to principal axis after passing through the lens, passes through the convex, another ray of
light which passes through optical centre undeviated. When these rays are produced backward
meet and formed an image A”B” where the object is placed.
This image on the same side of the lens, large in size, virtual and erect.
Q13. Write down the construction and working of an Astronomical Refracting Telescope?
Construction :
An Astronomical Telescope is comprised of two convex lenses. The lens facing the object is called
objective. It has a large focal length and wide aperture. The lens which is placed close to the eye is
called eye-piece. It has a short focal length.
Working :As these heavenly bodies are at a very large distance from the earth, so the rays coming from then
will be parallel so they are focused by the objective at its principal focus and image of the star is
formed. The image is real, inverted and small in size. The eye-piece is adjusted in such a way so
that the image formed by the objective is focussed within the focal length of eye-piece. The image
formed by eye-piece is virtual image which is highly magnified. This final image is inverted with
respect to real object but for astronomical objects it does not make any difference.
Used:It is used by Astronomer for seeing heavenly bodies
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Q14. Write down the construction and working of a photo graphic camera.
PHOTO GRAPHIC CAMERA:A photographic camera is comprised of a light proof box which has been blackend from the inside
so that stray light may be absorbed. In an ordinary camera a convex law is fitted on the front side
but in costly cameras a combination of lenses is used. The function of lens or combination of lenses
is to produce a real and inverted image of the object at the other end on light sensitive film or
plate. If we want to get a sharp image then the lens should be moved in or out with the help of
mechanical device. There is an arrangement of a diaphragm and shutter for controlling the light
which is allowed to enter the camera. A shutter of variable speed and a diaphragm of changing
aperture control the lens and amount of light entering into the camera when the camera is not in
use, the shutter remains closed. The shutter s allowed opening for a fraction of second when we
press the button for taking the photograph.
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Chapter-13
REFLECTION OF LIGHTREFLECTION:When a ray of light travelling in one medium meets the surface of another medium obliquely
some or all the light may be turned back into the first medium.
This is called “Reflection of Light”.
LAW OF REFLECTION:
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The two laws of reflection are.
The incident ray, the reflected ray and the normal at the point of incidence all lie in one plane.
The angle of incidence is equal to angle of reflection.
Q2. Differentiate between regular and irregular reflection?
Regular Reflection Irregular Reflection
Reflection of light from a smooth
surface is called regular reflection.
Reflection of light from a rough
surface is called irregular reflection.
All parallel rays of light reflected in
the same direction.
All parallel rays of light are
randomly reflected in different
directions.
Due to the regular reflection images
are formed.
Due to the irregular we can see non-
luminous object.
Reflecting surface is not visible. Reflecting surface is visible.
Q3. What are the importance of irregular reflection?Irregular reflection plays an important role in nature.
It is due to the irregular reflection that we are able to see the non-luminous objects.
It is due to this fact that sunlight reach us before sun rise and persists for some time even after
the sun set.
Q4. Describe the characteristics of an image formed by a plane mirror?
CHARACTERISTICS OF AN IMAGE FORMED BY A PLANE MIRROR:
Image formed by a plane mirror is erect and virtual.44
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Size of image formed by a plane mirror is equal to the size of the object.
Image formed by a plane mirror is laterally.
Image formed by a plane mirror is as far behind the mirror as the object in front of it.
Q5. Define the following? Spherical mirror, concave mirror, convex mirror, pole, radius of curvature, principal focus,
focal length & aperture
SPHERICAL MIRROR:
A spherical mirror is a portion of the surface of a polished hollow sphere.
CONCAVE MIRROR:
If the spherical mirror is polished from outside then this mirror is called concave mirror.
The centre of curvature lies in front of reflecting surface.
It converges the rays of light, therefore formed a real image.
CONVEX MIRROR:
If the spherical mirror is polished from inside then this mirror is called Convex Mirror.
Centre of curvature lie behind the reflecting surface.
It diverges the rays of light, therefore it is called diverging mirror.
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POLE:
The centre of the reflecting surface of the mirror is called “Pole” of the mirror.
CENTRE OF CURVATURE:
It is the centre of sphere of which the mirror is a part is called “Centre of Curvature”.
RADIUS OF CURVATURE:
Radius of that sphere of which the mirror is a part is called “Radius Of Curvature” .
PRINCIPAL FOCUS OR FOCUS:
It is the point where parallel beam of light after reflection from the mirror either actually
converges to that point or appears to diverge from that point. It is denoted by “F”.
Focus of concave mirror is called Real Focus.
Focus of convex mirror is called Virtual Focus.
FOCAL LENGTH:
The distance b/w the pole and focus is called “Focal Length” of the mirror. It is positive in concave
mirror and negative in convex mirror.
APERTURE:The diameter of the circular boundary of the spherical mirror is called aperture.
Q6. Differentiate b/w Real and Virtual image?
Real Image Virtual Image
An image is said to be real, if the rays
of light actually pass through it.
Virtual image is only visible to the
eye and a reflected ray of light
appears to come from that from that
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point.
It can be received on the screen. It cannot be received on the screen.
Real images are inverted. Virtual images are erect.
Distance of real image is taken
positive.
Distances of virtual images are taken
negative.
Q7. Explain with the help of a ray diagram, the nature, the size and the position of an image
formed by a concave mirror when an object moved from infinity to pole of the mirror?
Case I: When An Object Is Placed At Infinity:
Position of Image = the image is formed at focal point
Size of Image = extremely diminished
Nature of Image = Real and inverted
Case II : When An Object Is Placed Beyond “C”:
Position of Image = Image is formed b/w focal point and centre of curvature.
Size of Image = Small in size
Nature of Image = Real and inverted
Case III : When An Object Is Placed At “C”:
Position of Image = Image is formed at “C”
Size of Image = same in size
Nature of Image = Real and inverted
Case IV : When an Object is Placed between “F” & “C”:
Position of Image = Image is formed beyond “C”
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Size of Image = Image is magnified
Nature of Image = Real and inverted
Case V : When An Object is Placed at “F”:
Position of Image = Image is formed at infinity
Size of Image = Image is highly magnified
Nature of Image = Real and inverted
Case VI : When An Object Placed b/w “F” And Pole:
Position of Image = Image is formed behind the mirror
Size of Image = Magnified
Nature of Image = Virtual and Erect
Q8. Explain with the help of ray diagram, image formed by convex mirror?Position of Image = Image is formed behind the mirror
Size of the Image = Small in size
Nature of the Image = Virtual and erect
Q9. Derive the mirror equation 1 /f = 1/ p + 1/ q .
In order to derive a relation b/w focal length, object distance and image distance, consider an
object AB placed in front of a concave mirror b/w
Focus and centre of curvature. By considering two incident rays AO and AP reflected from the
mirror and formed an image A’B’.
In the above figure APB and A’PB’ are similar triangles, therefore
A’B’ = B’P
AB = BP
A’B’ = hi (Height Of The Image)
AB = ho (Height Of The Object)
hi = q ( B’P = q )
ho = p 1 ( BP = p )
As PFD and A’FB’ are also similar triangles is
A’B’ = B’F48
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PD PF
A’B’ = B’P - PF
PD PF
As PD = AB (Opposite sides of the rectangle)
hi = q-f
ho f
Comparing eq. 1 and 2 we get
q = q – f
p f
qf = p ( q – f )
qf = pq – pf
Dividing whole eq. By pqf
qf = pq - pf
pqf pqf
qf = pq - pf
pqf pqf pqf
1 = 1 - 1
p f q
1 + 1 = 1
p q f
1 = 1 + 1
f p q
Q10. Give some uses of spherical mirrors?There are several particles uses of spherical mirror some of which are mentioned below.
SHAVING MIRRORS:A concave mirror produces erect and magnified image when an object placed within the focal
length, therefore it is used as shaving mirror.
USE IN MEDICAL EXAMINATION OPHTHALOMOSCOPE:Doctors use concave mirrors for the examinations of ear, nose, throat and eyes of the patients in
ophthalmoscopes.
USE IN MICROSCOPE:Concave mirrors are used to throw light on the slides in a microscope so that the slides can be
viewed more clearly.
USE IN SEARCH LIGHTS AND HEAD LIGHTS:Concave mirrors are used to focus light in the case of search lights and head lights of automobiles.
USE IN TELESCOPE:
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The concave mirror are used as objective in big telescopes
USE FOR REAR VIEW:Due to the diverging property of a concave mirror is used in automobiles to have the rear view.
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Chapter-12
“WAVES AND SOUND”Q1. Define Vibratory. Simple Harmonic motion and positive that a body attached to an
elastic spacing execute. Simple Harmonic Motion?
Simple Harmonic Motion:The periodic motion, in which acceleration is directly proportional to displacement and the
direction of the acceleration is towards the mean position is called Simple Harmonic Motion.
Explanation:Let an object of a mass “m” is attached to a horizontal spring is placed on a friction less surface as
shown in figure.
Let a force is applied, due to which the body is displaced by a distance x.
According to Hook’s Law Applied force
F x
According Force or F = k x
Where ‘k’ is spring constant.
But due to elasticity the spring, the spring opposes the applied force and this opposing force is
called Elastic Restoring Force.
The elastic restoring force (F) is equal to applied force but opposite in direction, therefore
Elastic Restoring force = - (Applied Force)
F = - k x i
If “a” is the acceleration of body and “m” is the mass of the body then according to Newton’s
second law of motion
F = ma ii
Comparing (1) and (2) ma = -k x
Therefore a = - k x
m
Since k / m is constant
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Therefore a = - (constant) x
Or a -- x
This shows that acceleration “a” of the body is directly proportional to its displacement and is
directed to mean position.
Hence the motion of body under elastic restoring force is S.H.M
Q2. Prove that vibratory motion of Simple Pendulum is Simple Harmonic Motion?
Simple Pendulum:An ideal Simple pendulum consists of a point mass suspended by a weight less and in extensible
string from a fixed point.
Pendulum As A Simple Harmonic Oscillator:When we displace a pendulums bob from its mean position “O” to a new position “A” and then
released it will move towards “O” and due to inertia it will not stop at “O” and moves towards a
new position “B”.
The whole process is repeated again and again. “A” and “B” are the extreme positions of bob and
potential energy is maximum it that points. This potential energy is converted into K.E. when bob
moves from “A” to “O” or “B” to “O” and therefore, K.E. is maximum at “O”.
At “A” or “B” K.E. of bob is zero and it is maximum at “O”, therefore the bob accelerates when
moves towards “O”.
If we increase the displacement of bob the acceleration of bob will also increase.
From the above discussion it is proved that acceleration is directly proportional to displacement
and the direction of acceleration is towards the mean point.
Conclusion:Vibratory motion of Simple pendulum is Simple harmonic motion.
Q3. Define resonance; give at least two examples from you daily life?
Resonance:When the frequency of driven force is exactly equal to the natural frequency of the oscillator, the
driven force imparts the maximum energy to the oscillator, resulting a considerable increase in
amplitude of vibration. This is called Resonance.
Examples Of Resonance:An interesting example of resonance is that of swing while enjoying a swing we apply force by the
special movement of our body at a particular position in every vibration. The result is increase in
the amplitude of swing.
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When an opera-singer sings at a very high pitch, glass are caused to break. This is because
frequency of the note is same as the frequency of glass, resulting an increase in amplitude of
particles of glass and the glass will break.
Q4. a)Define Wave Motion?
b) Define Transverse and Longitudinal Waves and Explain with the help of an example?
Wave Motion:The mechanism by which energy is transferred from one place to another is called “wave motion”.
Transverse Waves:Transverse waves are those waves in which the disturbance travels in a direction perpendicular to
the direction of oscillation of particles.
Examples:We can produce transverse waves in a rope by fastening the rope at one end, and holding the other
end.
If we give a sudden up and down jerk in a direction perpendicular to its length. A wave pulse travels
from the jerk end to the fixed end of string. This wave produces elevation and depressions called
crest and trough respectively.
The distance between two consecutive crest or trough is known as wave length and it is denoted by
Greek Symbol “” (Lambda).
Longitudinal Waves:Those waves in which particles of elastic medium are vibrating in the same direction in which wave
is travelling called Longitudinal Waves.
Examples:Consider a horizontal wave on a spring produced by waving the spring back and for with one’s
hand. This is longitudinal wave in which particles of the medium vibrate back and forth along the
direction of wave. The portions where the particles come closer are called compression and when
these particles come back to its original shape is rarefaction. The distance between two consecutive
compressions is called Wave Length.
Q5. Differentiate between Transverse and Longitudinal Waves.
Transverse Waves Longitudinal Waves
In transverse waves the particles of the medium
liberate in a direction perpendicular to the
direction of motion of waves.
In longitudinal waves the particles of the
medium vibrate in the direction of motion of
waves.
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Trough and Crest are produce in transverse
waves.
Compression and rarefaction are produced in
longitudinal waves.
In transverse waves the distance between two
identical positions of two consecutive troughs or
crests is known as Wave Length.
In Longitudinal waves, the distance between two
identical positions of two consecutive
compressions’ or rarefactions is known as Wave
Length.
It can be produced in solid, liquid and also in
space.
It can be produced in solid liquid and gas only
but not in vacuum.
Microwaves, Radio Waves, Waves on the surface
of water are examples of transverse waves.
Sound wave and compress ional waves in a
spring are examples of longitudinal waves.
Q6. Define the terms Wave Length, Frequency and Time Period and prove that V=f .
Wave Length:It is the distance between two consecutive crest and trough. It is denoted by a Greek symbol “”
(Lambda).
It is also defined as the distance between two particles which are in phase (having same frequency
and same direction of motion).
Frequency:It is number of vibrations executed by an oscillating body in one second is called frequency. Its S.I.
unit is vibration/s, cycles/s or hertz. Frequency and time period are reciprocal of each other i.e.
f = 1/T
Time Period:It is the time required to complete one vibration or one oscillation. It is denoted by “T”.
Time period and frequency are reciprocal of each other i.e. T = 1/f
Proof V= f : The velocity of wave (whether of transverse or of longitudinal) is defined as the distance through
which any part of the wave disturbance moves in unit time.
Consider a wave of wave length “” passing through a point in time “t” then
S =
Time = T
If “V” is representing speed of wave then: V = S /t Or V = / T
Or V = 1/ T.
As we know that reciprocal of time is frequency; therefore, V = f
The above relation is called wave equation. It is true for any types of wave. Such as water waves,
Sound waves and radio waves etc.
Q7. Define Interference, Constructive destructive interference of waves and stationary
waves?Interference:
It is the interaction of two waves passing through the same region of space at the time.
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Constructive Interference:
If two waves interfere in such a way that crest of one wave falls on crest 0of second wave or trough
of one wave falls on trough of second wave then their combined effect is greater than either of two,
waves this is called constructive interference.
Destructive Interference:
If two waves interfere in such a way that crest of one wave falls on trough of second wave then
they cancel the effect of each other and there is no wave will be observed on the surface of water.
This is called destructive interference.
Stationary Waves:
When two waves of same frequency and wave length travelling in the same medium in opposite
direction meet with each other, form a new wave, in which particles of the medium do not transfer
the energy from one point to another, These special waves are called stationary waves or standing
waves. These wave form nodes and Antinodes.
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Chapter #
SOUNDSound:Psychologically, sound is the sensation produced in ear. Physically, it is said to the stimulus, due to
vibratory sources, and capable of producing the sensation of hearing in the auditory system.
Therefore, sound waves are the longitudinal waves that are capable of producing the sensation of
hearing.
Conditions Necessary To Hear Sound:Sound is a form of energy which travels in the form of longitudinal waves but all the longitudinal
waves are not sound waves. There are few conditions that must be fulfilled to detect sound.
a) Condition Necessary For Producing Sound:
Sound is produced only if a body is vibratory i.e. there is a vibratory source to produce sound
waves.
b) Condition Necessary For Propagation Of Sound Waves:
Sound waves required material median for the propagation.
C) Condition Necessary For Receiving Sound Waves:
Sound waves are received only if there is an auditory system i.e. a receiver like ear in human
beings.
d) Condition Necessary For Detection Of Sound:
Proper frequency range is required to detect sound waves. This frequency range is known as
Audible Frequency Range. It has different values for human beings and for other receivers
(organisms). The audible frequency range for human ear is 20 Hz to 20000 Hz.
Audible Sound:Those sound waves which can be detected are known as Audible sound. For an average human ear
an average human ear cannot detect the audible sound frequency ranges from 20 Hz to 20000 Hz
i.e. greater than 20000Hz.
Infra Sonic:Theses longitudinal waves having frequency less than 20 Hz are known as Infrasonic. These waves
cannot be detected by a human ear but can be caught by some other organisms.
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Ultrasonic:Sound waves having frequency more than 20000 Hz are known as Ultrasonic. An average human
ear cannot detect them because eardrum cannot vibrate with such a high frequency. However,
many species like bat-bugs and dolphin can hear sound with frequency more than 20000 Hz. Bats
and Dolphins can hear sound with frequencies above 100000.
Q2. Describe an experiment to prove that sound waves are produced by a vibratory source?Sound is always produced by some vibrating body. As the source vibrates mechanically about a
fixed point, the medium in the vicinity is alternately compressed and rarefied. The vibratory
object may be the prongs of a tuning fork, skin of a drum, wire in a piano or violin, a reed in
harmonium, a gong of an electric bell, air column in the vocal cord of human being etc.
Experimental Verification:Consider electric bell connected to an electric surface where the switch is turned on, the hammer
connected in the bell strikes to the gong (metallic disc) and sound is heard. The vibrations of
ringing bell can be demonstrated by bringing a pitch-ball suspended by fine thread close to it. The
pith-ball is thrown off as soon as it touches the bell.
Result:The above experiment proves that the ringing bell is vibrating about its mean position producing
alternative compressions & rarefaction in the medium.
Q3. What is meant by propagation of sound waves? Prove by an experiment.Whenever a body is vibrating, it produces a disturbance in the surrounding air. This disturbance
reaches our ear in the form of waves thus producing the sensation of sound. If there is no medium
around the vibrating body, the sound waves will not reach our ear and we will hear any sound.
Let us perform an experiment.
Experiment:Suspended an electric bell in a jar by its wire through a cork fixed in its mouth as shown in Fig.
Switch on the bell. We will hear the sound of the bell. Now start-removing air from the jar with
the help of the bell will start decreasing ultimately, bell. This experiment shows that air is
necessary for the propagation of sound in fact a material medium such as air, water metals etc., is
needed for the sound to travel from one place to another. Thus three things are necessary for the
sound (i) vibrating body (ii) some material medium like air, water etc. and (iii) receiver like ear.
Q4. Why does the flash of lighting seen earlier than the sound of thunder?It is a matter of common experience that the flash of lighting is seen earlier than hearing the
thunder of cloud. Similarly when a gun is fired, its sound is heard a little after seeing its flash. The 56
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reason is that light travels much faster than sound. Due to its slow velocity sound lags behind and
so it is heard a little after seeing the flash.
Q5. How you calculate the velocity of sound?Select two stations at a distance of 8 Km. to 10 Km. such that there is no obstacle between them
which can hinder the view. Fire a gun at station A and ask your friend at station B to start a
stopwatch on seeing the flash. The stopwatch should be stopped on hearing the sound of the gun.
The distance S between the two stations is already known. So the velocity V of the sound can be
calculated by the formula:
V = S / t
The mean of these time intervals is calculated to find the exact value of velocity of sound. The
distance between the two stations A and B S.
Average Time t = t1 + t2 2
Velocity Of Sound V = S / t
The velocity of sound in air at 0oC is 330 m/s. The velocity of sound in water is 1450 m/s and in
iron it is 5130 m/s. The velocity of sound is increased with the increase in temperature.
Q6. What is the difference between musical sound and noise?
Musical Sound Noise
Musical sound which has a pleasant
effect on our ears.
Which has unpleasant and jarring effect
on our ear?
In musical sounds there is a regularity in
the variation of frequency and amplitude
Noise has abrupt changes in amplitude
and frequency and there is no regularity
in the variation of frequency.
Sound of different musical instrument,
which are operating in a right manner,
of a song of Mehdi Hassan or Noor
Jehan are some examples of musical
sound.
Barking of dogs, ratting of machines,
sound produced by rickshaws are some
examples of noise.
Q7. Describe the characteristic of musical sound?Characteristics of musical sound are as follows:
Loudness of Intensity:1. The characteristics of a sound by which a loud and a faint sound can be disguised are
called loudness.
2. Loudness depends upon intensity and also upon the sensitiveness of the ear.
Loudness or Intensity depends upon the following factors:
The Amplitude Of Vibrating Body:If the amplitude of the vibrating body is large, the sound will be loud. On the other hand if the
amplitude is small then the sound will be faint. When we beat a drum forcefully the membrane
vibrates with large amplitude and a loud sound is heard.
Area Of Vibrating Body:
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A louder sound is produced if the surface area of a vibrating body is large. The loudness of a school bell is more than
that of a house bell.
Distance Of Sounding Body:If we are standing near a rail road track we will hear a faint sound of a train which is far away from us. As it
approaches us the sound becomes louder and louder. The sound will be loudest when the train passes by us. After
passing by us, as the train moves away from us the sound will start becoming feeble and feeble again.
Pitch:It is a sensation that depends upon the frequency. A shrill sound is produced by a source of high frequency whereas
the pitch is lower if the frequency is lower. Pitch does not depend upon loudness or quality. The voice produced by
ladies and children has high pitch because the frequency is high.
Quality Or Timber :It depends on the presence of overtones. The quality of sounds enables us to distinguish between two sounds having
the same loudness and pitch. Nature has provided different overtones in the voice of different persons. The humming
of a mosquito or a bee has low amplitude but high frequency.
Q8. Differentiate between Pitch and Quality?
Pitch Quality
The characteristics of sound by which a shrill
sound can be distinguish from a grave one is
known as the sound.
It is that characteristics of sound, which enables
us to distinguish between two sounds of same
loudness.
Pitch of the sound depends upon the frequency of
the sound.
It depends upon the wave form of the waves.
Q9. What is an echo? How is it produced?
Echo: “The sound is heard after reflection from a surface is called an echo”.
The repetition of sound produced due to reflection by a distant extended surface like a cliff, hill, well, building etc, is
called an echo. The effect of sound on the human ear remains for 1/10 th of second. Suppose, a person produces sound
and this sound is reflected from an obstacle at a distance ‘D’. The time taken by the sound to travel to the obstacle and
back is ‘t’. Velocity of sound is 330 m/s.
therefore, D = Vt 2D = 33
2D = 330 x 1 D = 33 = 16.5 ≈ 17m
10 2
It means that if the distance between the source of sound and the obstacle is less than 17 meters
(56ft.)
Q10. What is meant by Beats?
Beats:When two sound waves that differ from one another in frequency by a very small number. Then
sometimes we hear a loud sound where the compressions of the two waves meet and at other time
we hear a faint sound where the one wave falls upon the rarefaction of the other wave. This
phenomenon is called beats. The number of times we hear the rise and fall of sound per second is
called the beat frequency. The beat frequency is equal to the difference in the frequencies of the
two sounds.
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Chapter-15
NATURE OF LIGHT & ELECTROMAGNETISM
Q: Write a note on the following:
Newton’s Corpuscular theory of light
Wave theory of light
Quantum theory of light
Newton’s Corpuscular Theory:Sir Isaac Newton in 1675 presented a theory regarding nature of light. It is known as
Newton’s corpuscular theory of light.
According to this theory “A luminous body like the sun, electric bulb etc. continuously
emits minute invisible particles called corpuscles in all direction these corpuscles posses following
properties.
1. Travel in a straight line with a very high speed without being affected by the earth’s
gravitation.
2. Penetrate into the transparent medium.
3. Produce the sensation of vision when they strike retina.
4. Reflect back from a polished surface.
Achievements of Corpuscular Theory:With the help of this theory. Newton explains the following:
1. Propagation of light in a straight line.
2. Shadow formation.
3. Bending of light in a denser medium.
Draw Backs of Corpuscular Theory:1. Newton assumed that speed of light is more in denser medium than a rarer medium.
Foucault Proved that Newton assumption is wrong.
2. Newton assumed that higher the temperature of luminous body higher the speed of light.
This assumption is also proved wrong.
Huygens Wave Theory:Huygens presented another theory regarding nature of light. According to the theory:
Light is emitted theory from a source in the form of waves which
continuously propagated away from source.
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Achievement of This Theory: Reflection and refraction was successfully explained.
Present explained the rectilinear propagation of light.
Interference of light also proved by this theory.
Draw Backs of This Theory:It was known during those days that a medium is essential for the propagation of waves
therefore it was assumed that whole universe is filled with hypothetical medium called ether.
Morley and Michelson with the help of an experiment proved the Ether did not exist.
Maxwell’s Electromagnetic Theory:According to Maxwell light waves are electromagnetic i.e. they are rapidly moving electric
and magnetic fields which are perpendicular to one another. The propagation of electromagnetic
waves does not require any material medium. He proved that electromagnetic waves are of
transverse type.
Draw Backs of This Theory: The Maxwell’s theory could not explain the phenomenon of photo-electric effect.
Plank’s Quantum Theory:Quantum theory is simply a sort of revival of Newton’s corpuscular theory. According to
this theory light is a form of energy and travels in the form of energy packets called Photons.
Energy of each photon is given by E=h where h is the plank’s constant and is the frequency of
light. The energy of photon depends upon the frequency. Einstein gave a simple explanation of
photo-electric effect on this theory. Neil Bohr also used this theory to explain the spectrum of
Hydrogen atom. Quantum theory could not explain interference and polarization.
Dispersion Of Light:When white light is allowed to pass through a prism it is decomposed into several colors
which appear as a band on the screen. The splitting up of light into it’s constituent colors is called
dispersion of light. The band of colors seen on the screen is called spectrum.
Monochromatic And Ordinary Light:Sunlight or white light is called ordinary light while the light which contains only one
colour or of simple frequency is called monochromatic light.
Rainbow:After rainfall tiny water droplets remain suspended in the air and they behave like prism and
disperse the sunlight fallen on to it into seven different colors. If the sun is at the bank of the observer and
light rays fall obliquely on the droplet then rainbow is seen. It is an spiral arc of colors which appear when
sunlight is dispersed by droplets.
Under favorable conditions several bows may be seen. The brightest bow is called primary bow it
shows brilliant colors of the spectrum of the sunlight. It is red on the outer and violet on it’s inner edge.
Visible and Invisible Spectrum:
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When whit light is allowed to pass through a glass prisms it gets split it into its constitute
colors and a bend of colors is seen on the screen. This color bend is called visible spectrum. But
there are several other types of waves in the spectrum at both the ends of visible spectrum
corresponding the waves whose frequency greater than violet waves is called “Ultra Violet” and
the portion of invisible spectrum corresponding the waves whose frequency less than that of red
are called “infrared”.
Emission Spectra:When a substance strongly heated it starts emitting radiation. Spectrum thus form the
radiation is called emission spectrum.
It is found that the substance in automatic state emits radiation which produced sharp and
district lines in the spectrum. Such a spectrum is called line spectrum.
When a temperature of a solid goes on increasing the number of lines seen in the spectrum
also increases. The solid becomes white hot it emits nearly all the colors and so we get what is
continuous spectrum.
Luminous gases or vapors when heated produced a spectrum in which we see groups of
closely packed lines on bends such a spectrum is called bend spectrum.
Photon:According to Quantum Theory, light is emitted and absorbed in the form of energy
packets. These energy packets are known as Photons. Energy of photons is given as follows:
E = h
Where “E” is energy, “h” is Plank’s constant and “” is the frequency.
Q Explain Electromagnetic Spectrum?When we get electromagnetic spectrum then we get the following wave length spectrum of light.
Radio Wave:These waves consist of a large range of wavelength form a few millimeters to several
meters.
Microwaves:These waves of shorter wave lengths between 1mm and 300m. It is used in radar and
microwaves ovens.
Infrared Waves:These waves are radiated by hot bodies at different temperature. Its wavelength is 10
micrometer to 10-5m.
Visible Waves:Their wavelength ranges from 380 nm down to 60 nm. These are emitted by hotter stars
having a mean temperature greater than 25000 oc.
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Ultra Violet Waves:Their wavelength ranges from 380 nm down to 60 nm. These are emitted by hotter stars
having a mean temperature greater than 25000 oc.
Gamma Rays:Their wavelength is less than 10-11 m. They are emitted by the nucleus of certain
radioactive substance.
Green House and Its Effect:
Definition:
Due to small amount of water vapour and carbon dioxide in the atmosphere, it is trapping
heat energy and this effect is called Green House Effect.
Explanation:
The major part of energy, which receives earth from the sun, is absorbed by the
atmosphere. Due to these gases of atmosphere and surface of water is heated. When earth is
heated, it radiates energy in the form of infrared waves of larger wavelength.
Dust and gas:
Molecules scatter some light to space. The small amount of water vapors and carbon dioxide in the
atmosphere is transparent to visible light, but lower part of atmosphere. An analogous effect takes place
in green houses where the glass of green house allows light to pass through and heat the enclosed ground.
Since glass is relatively opaque to infrared radiation, the heat is trapped in the green house. Sometimes
green house effect is so great that we can feel it. For example, in winter it is much warm at night in the
presence of thick cloud layers. If such layers dissipate and clean air moves in the temperature of the
surrounding, it is sure to drop as the ground radiates its heat energy unhindered into space.
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HEAT
Heat Temperature
Heat is a form of energy which is
transferred from one point to another
due to difference of temperature.
It is the measures of average Kinetic
Energy of molecules.
It is measured in Joules. Unit of temperature is Kelvin or oC or oF.
It is measured by Calorimeter. It is measured by thermometer.
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It depends upon amount of substance. It does not depend upon amount of
substance.
Q2. Write down the construction and working of the following.
Ordinary Liquid In Glass Thermometer.
Clinical Thermometer.
Maxima And Minima Thermometer.
Thermos Flask.
Ordinary Liquid-Glass Thermometer:The most common type of thermometer is the liquid in glass thermometer as shown in
figure it consists of a glass stem with a capillary tube, having a small bulb at one end. The bulb
and part of the capillary tube are filled with a liquid, usually mercury or alcohol colored with a
red dye to make it visible. The upper end of the capillary tube is sealed so that liquid will neither
spill nor evaporates from the tube. On heating, the liquid expands and rises in the tube. In order
that the liquid may expand freely in the upper part of the tube, air is removed from it before
sealing the upper end. A temperature scale is marked on the glass stem to indicate temperatures
corresponding to various levels of the liquid in the tube. The liquid –in-glass thermometer
commonly used in a laboratory.
Clinical Thermometer:Purpose Of Clinical Thermometer:
A clinical thermometer is used to find the temperature of human body by placing the bulb
under the tongue or in the arm pit. The normal body temperature is about 37oC. The temperature of
a sick person varies slightly from this value. For this reason a clinical thermometer has a limited range
of calibration usually 35oC to 43oC (95oF to 110oF)
Construction And Working:
The glass stem of the clinical thermometer has a narrow bend or constriction in its capillary bore
near the mercury bulb.
This helps to stop the mercury thread moving back towards the bulb after the thermometer
is removed from the patient’s mouth and the temperature can be read easily.
Maxima And Minima ThermometerConstruction:
This thermometer consist of a bulb “X”, completely filled with alcohol, a “U” tube “Y”,
contained mercury, another bulb “Z”, partially filled with alcohol, and two steel indexes “A1”
and “A2”. Temperature scales are provided against each limb of the U tube. The alcohol in “X”
has the largest volume compared to the volume of mercurying and alcohol in “Y” and “Z” respectively.
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Working:
When the temperature rises, the alcohol in “X” expands and pushes the mercury column
down, with the result that the index A2 is forced up by the mercury meniscus. Thus the lower end
of A2 indicates the maximum temperature reached, this being read from the scale. As the temperature
falls, the alcohol in X contracts and owing to the pressure of alcohol vapors in Z, the index A1 is forced
up by the mercury column. Thus the lower end of A1 indicates the minimum temperature reached.
Use:
It is use in green houses, food storage and methodological stations.
Thermos Flask:Definition Of Thermos Flask:
“Thermos Flask is a pot designed to prevent heat loss from the fluid inside it, due to all of the
three heat transfer mechanism. Similarly it prevents the heat from outside, getting into the material”.
Construction Of Thermos Flask:
It consists of double wall glassed vessel, which is silvered on the outer surface of the inner wall
and on the surface of the outer wall. The space between the walls is evacuated, and is then sealed. The
glass vessel is enclosed in a metal case such that it rests on a cork at the bottom of the case, and is
secured at the neck with a pad of felt or a ring of rubber.
Working Of Thermos Flask:
Glass is a relatively poor thermal conductor while cork, air are felt between the glass vessel
and the metal case are all bad conductors. Thus heat from a hot liquid kept in the glass vessel cannot
rapidly pass to the metal case. The cork in the neck of the vessel, and the cup over that, prevent loss of
heat by convection. Moreover, the silvering on the outside of the inner wall makes that wall a bad
radiator, while that on the inner surface of the outer wall tends to reflect back any heat that is
radiated. Consequently hot or cold drink in the thermos flask remains hot or cold for relatively long
time.
Q3: Define the following:
Conduction
Convection
Radiation
Thermal Conductivity
Conduction:Conduction is the transfer of heat energy through a solid body due to the molecular interactions.
Convection:Convection is the transfer of heat from one part of a fluid to another by the movement of the
fluid from the hotter to the colder part.
Radiation:
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In this process heat energy is transfer from hot place to cold place without any material
medium. The hot object emits radiation which carries away energy. When these radiation fall
on an object, their energy is transferred to the latter in the form of heat.
Energy transfer from sun to earth is an example of radiation.
Thermal ConductivityThermal conductivity can be quantitatively defined as the amount of heat conducted for one
second through a meter cube of the substance whose opposite faces are maintained at a temperature
difference of 1oC.
Mathematically
K=Q L / A T t
Its unit is J oC-1 m-1 s-1
Q4. Define Co-efficient of Linear Expansion and prove that L2=L1 {1+ T}
Co-efficient Of Linear Expansion:“It is the change in length per unit length per degree rise in temperature”.
It is denoted by “”.
Mathematically
= L / L1 T
L2 = L1 {1+T}
Consider an iron rod of length L1, at temperature T1 oC. It is heated to certain temperature
T2 and its length becomes L2.
Change in length = L = L2 – L1
Change in temperature = T = T2 – T1
Change in length per unit length per degree rise in temp = L2 - L1/L1T
Or = L / L1 T
Or L1 T = L
Or L = L1 T
Or L2 – L2 = L1 T
L2 = L1 + L1 T
L2 = L1 {1+ T}
Unit of Co-efficient of linear expansion is oC-1.
Q5. Define bimetallic strips and write note on the following
Bimetal Thermometer
Thermometer
Fire Alarm.
Bimetallic Strips:
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Before Heating After Heading
Brass
Iron
When two metallic strips of different thermal expansion are pasted together bimetallic strips
are formed i.e. Bimetallic strips of iron and brass.
Bimetallic Thermometer:As we know liquid glass thermometer have a low range of measurement because liquid
vaporize at low temperature and also glass melts. So it can not be used to measure high
temperature as above 500 oC. So bimetallic thermometer is used for the measure of higher
temperature.
Construction And Working Of Bimetal Thermometer:A bimetal strip can be used to make a simple thermometer which is tough but easy to read
as compared with liquid-in-glass thermometers. It consists of a bimetal strip in the form of a long spiral.
One end of the spiral is kept fixed while a light pointer is attached to the other, as shown in Fig.
When the temperature rises, the bimetal strip coils itself into an even tighter spiral due to different
expansion rates of the two metals which form the bimetal strip, and the pointer moves across the
temperature scale.
Thermostat:Thermostat are devices which control temperature in a certain space e.g. in refrigerators,
electric ovens, motor car engines etc. To maintain the temperature of air inside the room at a
comfortable level, thermostats are used with room heaters or air- conditioners.
Construction And Working Of Thermostats:The essential parts of a thermostat are shown in Fig. Suppose this thermostat is connected to
an electric room heater. As the temperature of air inside the room rises, the bimetal strip bends and
the electrical contact is disconnected. This switches off the heater. When the room temperature falls,
the bimetal strip cools and straightens. As the contacts touch each other, the heater is switched on
again. In this way the thermostat switches the heater on and off to keep the room at a more or less
steady temperature.
The desired temperature is selected by mean of a control knob. If the control knob is
screwed in wards, the bimetal strip has to bend further before the contacts disconnected. Thus
the room needs to be warmer before the heat is switched off.
Fire Alarm:Another very useful application of a bimetal strip is a fire alarm. A model fire alarm is shown
in fig. one end of a bimetal strip is firmly fixed while the other end is free. One terminal of a 6 volt
bulb or an electric bell. The other terminal of the battery is connected with a metallic contact which is
just above the free end of the strip. The heat energy given off when a fire starts raises the
temperature of the bimetal strip. The free end of the strip bends towards the contact and on
touching it electric current flows through the circuit. The bulb therefore, light up or in case of a bell, it
rings, to signal a warning about fire.
Q6. What do you know about?
a) Anomalous Expansion Of Water
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b) Why do fish and other aquatic animals in oceans and seas survive in extremely cold
water?
c) Why do water pipes burst in winter seasons in cold regions?
d) Why rocks do are break in cold regions.a) All the substances contract on freezing and expand on heating but water has a strange
behavior between 0oC to 4 oC. It expands when its temperature falls from 4oC to 0oC and contract
when it is heated from 0 oC to 4oC. This strange behaviors of water is called Anomalous Expansion of
water.
Effect Of Anomalous Expansion Of Water:The effect of anomalous expansion of water is important in nature & everyday life. Some of them
are discussed here briefly.
In Winter, the water ponds, lakes and seas in the area close to the north and south poles of the
earth cools down as the atmospheric in temperature falls. The cooler and denser water at the surface
initially flow to the bottom. When the temperature at the surface reaches 4oC, this downward flow
of water ceases. If the atmosphere temperature further falls below 4oC the water at the surface expands,
becomes lighter and therefore does not sink. As the water freezes at the surface it remains there
while water near bottom remains at 4 oC. This help fish and other forms of marine life to survive an
wither season.
During the rainy season, a lot of water seeps through the numerous cracks & fissures in rocks.
In winter expands freezing. The rocks are therefore subjected to high pressure and are broken up.
In colder climates, the water supplies pipes burst, when the atmosphere temperature falls
below 4oC. This is because water in the pipes expands, and exerts enormously pressure on the walls
causing damage to the pipes.
Q7. State and following law?Explain General Gas Equation and write its mathematical form.
Boyle’s Law:“Volume of a given mass of gas is inversely proportional to the pressure, if the temperature
is kept constant”.
Mathematical Representation:If “V” denotes the volume and “p” stands for pressure then
V 1 / P
Or V = (Constant) 1 / p
Or VP= Constant
Graphical Representation:The pressure volume graph is a curve line shows that they are inversely proportional
quantities.
Charles Law:
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Volume of a given mass of a gas is directly proportional to its absolute temperature, provided that
pressure is kept constant”.
Mathematical Representation:If “V” and “T” stands for volume and temperature receptively then
V T
Or V = (Constant) K
Or V/T = Constant
Graphical Representation:The relation between volume and temperature for a given mass of a gas on graph is straight line
which shows that they are directly proportional to each other.
Q12. What is refrigerator write down its construction and working?
Refrigerator:It is device which is used to cool things and to preserve for a certain period of time e.g. food,
fruits etc.
Construction:Refrigerator uses gases which liquefy under pressure at normal temperature usually Freon
gas is used as a refrigerant. Refrigerator consist of three parts
Condenser
Evaporator
Compressor
Working:The gas is first compressed and fed into the condenser. There it liquefies under pressure and is
then let through a valve into a evaporator. In evaporator Freon evaporates under normal pressure
absorbing heat from the area surrounding the evaporator, thus cooling
it down. It is again brought to the condenser with the help of compressor. Freon loses its
heat in condenser where it again liquefied. This process is continuously repeated in this way
temperature inside evaporator becomes lower and things are preserved for long time.
Expansion Of Liquid:When liquids are heated, they expand and their volumes increases and on cooling contraction
takes place. We know that liquids are always contained in some sort of container which is made up
of solid. So when liquid is heated, first heat is absorbed by the solid container and its cubical
expansion takes place. Then after sometimes the liquid inside starts getting heat and its cubical
expansion takes place. When the expansion of the solid vessel occurs, the level of liquid inside the
container lower due to increased capacity of the container. Then on further heating the liquid level
rises as it starts absorbing heat from the vessel.
Thus while studying expansion of liquids we come across two types of expansion.
The apparent expansion.
The real expansion.
Their coefficients are as defined as follows.
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1. The Coefficient Of Apparent Expansion: Its is the rate of apparent expansion or apparent change in volume per unit original volume per
degree rise in temperature its is denoted by Ya.
2. The Coefficient Of Real Expansion: It is the rate of real expansion, or the real increase in volume per unit original volume per
degree rise in temperature. It is denoted by Yr.
The coefficient of apparent expansion always slightly lower than the coefficient of real
expansion by rate of cubical expansion of the container.
Yr = Yc + Ya
Where Yc is the coefficient of cubical expansion of the container.
Specific Heat :It is the amount of heat absorbed or given out by one kg of a substance when it is heated or
cooled through 1oC.
Spht = Amount of heat absorbed / given out
Mass x rise / fall in temperature
C = Q / mt
Q = mCt
where c = Specific Heat
m = Mass of the Substance
t = rise or fall in temperature
The SI unit of specific heat is J/kg oC.
Calorie:It is the amount of heat absorbed/given out by 1gm of water through 1oC. It is equal to 4.2
Joules.
Kilo Calorie:It is the amount of absorbed / given out by 1Kg, of water when heated / cooled through 1oC.
It is equal to 4200 Joules.
There is another unit of heat called British thermal unit (BTU)
1 BTU =1054Joules.
The Law Of Heat Exchange:When two bodies at different temperature are brought in contact, heat starts flowing from a
body at higher temperature towards a body at lower temperature. In this way hot body loses heat
and cold body gains it. The law of heat exchange states that “Heat lost by hot body is equal to heat
gained by cold body.
Determined of specific heat of solid by method of mixture:
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In this method a special type of container called calorimeter and thermometer are used to note
the temperature of the contents.
In this method the solid of which the specific heat is required, is heated through a known
temperature in the test tube of hypsometer. In the mean time the empty calorimeter with stirrer is
weighted. 2/3 of volume of Colorimeter filled with water and then weight it. The difference gives mass
of water. The temperature of calorimeter is noted. Which is also the temp of water beside it. Hot
solid from the test tube proved with Colorimeter and stirred for some time to achieve a constant
temperature. The final temperature of the mixture is noted. Again after weight the Colorimeter and
y the following calculation find specific heat of solid.
The following data is obtained.
Mass Of Empty Calorimeter with stirrer = m1 kg.
Mass Of Calorimeter stirrer and water = m2 kg.
Mass of water = (m2 – m1) kg.
Mass of mixture = m3 kg.
Mass of solid = ( m3 – m2 ) Kg.
Initial temperature of Cabrimetre = t1 oC (Room Temperature)
Initial temperature of water = t1 oC (Room Temperature)
Initial temperature of solid = t2 oC (Temp in the Hypsometer)
Final temperature mixture = t3 oC
Fall of temp of solid = (t2 – t3) oC
Rise of temp of Colorimeter = (t3 – t1) oC
Rise in temp of water = (t3 – t1) oC
Specific Heat Water = 4200 J/Kg oC
Specific Heat Of Colorimeter = C1, J/Kg. oC (given)
Specific Heat Of solid = C =? (Required)
Heat lost by solid = sp heat of solid of x fall of colorimeter temp.
Ht lost by solid =
Heat gained by Calorimeter = spht x mass x rise in temp.
Ht gained by Calorimeter = c1 m1 (t3 – t1)
Heat gained by water = 4200 x (m2 – m1) x (t3 – t1)
According to law of heat exchange
Heat lost by solid = Ht gained by cm + heat gained by water.
( m3 – m2 ) C2 (t2 – t3) = C1m1 (t3 – t1) + (m2 – m1) 4200 (t3 – t1)
C2 = ( m2 – m1 ) x 4200 ( t3 – t1 ) x m1 C1 ( t3 – t1 )
(m3 – m2) (t2 – t3)
Melting Point:The temperature at which the melting of a solid to liquid occurs is called its melting point.
Latent Heat of Fusion:It is the amount of heat required to convert unit mass of a solid into liquid at its melting point
with out rise in temperature. Or
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Heat given out by unit mass of a liquid to change into solid at its freezing point with out fall in
temperature is called latent heat of fusion.
Lf = Q / m
When ever change of state occurs, there is no rise or fall in temperature.
Explanation On The Basis Of Kinetic Molecular Theory:
When a solid is heated its molecular motion is increases, a result the temperature rises. If the
solid continues to absorb heat, a stage come when the vibration of the molecule increases so much
that it over comes the intermolecular force of attraction which keeps the body bound together as solid.
At this point solid starts changing it state of liquid. Any further addition just helps in breaking up
the bonds of attraction between the molecules. The energy of the molecule does not increase on the
average the temperature remains constant till all the solids are broken.
Latent Heat of Vaporization:It is the amount of heat required to convert unit mass of a liquid into vapors at its boiling point
with out rising temperature. Or
The heat given out by unit mass of vapors to change into liquid at their point of condensation
with out fall in temperature.
Lv = Q / m
Explanation On The Basis Of Molecular Theory:When a liquid is heated its molecular motion increases in temperature. When the liquid
continues to absorb heat a stage come when the intermolecular force of attraction is over come and any
further addition of heat does not raise its temperature but change of state starts taking place till the
hole liquid change to vapor.
Effect Of Pressure On Melting Point (Regelation):Substance which expands on freezing when subjected to pressure, melt before their melting point
on removal of pressure they again freeze at their freezing point. This process is called regelation.
To illustrate we takes the ice block supported on stands a wire is passed over it with weight
changes on the earth end. The layer of ice just beneath the wire due to pressure melt and skins
down. As the wire skins the pressure is removed and that layer freezes again. This process
continues till the whole wire passes through it and the block does not cut in to two.
Effect Of Pressure On Boiling Point:The boiling point of a liquid increases with pressure and vice versa. Water boils at 100 oC
when the pressure 760 mm Hg. Its pressure is reduced the boiling point decreases.
To illustrate this we take a flask half filled with water and heat it till it starts boiling. Let it
boil for some time so that sufficient steam may produce. Then stop heating and cork the flask. The
flask is then inverted on a stand and cold water is poured over it.
As we pour cold water the water inside the flask again starts boiling although we have stop
heating. This explained as, “When the heating was stopped there was pressure of steam (vapors) also
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to water and reduced the pressure on water and the boiling point also decrease water starts boiling
again below its boiling point.
Evaporation:The process of converting a liquid into vapors without boiling it called evaporation. Evaporation
takes place at all temperature.
Explanation On The Basis Of Molecular Theory:According to kinetic molecular theory, the molecules of liquid are in continuous motion due to
motion, they posses kinetic energy. The energy of all the molecules are not same. The molecules which
are near the surface of liquid due to continuous collision with other molecule acquire so much energy
that they over came the inter molecular force of attraction of the liquid and escape out of the surface of
liquid, leaving behind a fall in temperature of the liquid. Due to fall in temperature the cooling
effects is experienced.
Factors upon which rate of evaporation Depends
Rate of evaporation depends upon the following factors.
Temperature of the liquid:If the surface temperature is high rate of evaporation increase. While ironing the cloths, wet
cloths dry out quickly as the water evaporates quickly.
Nature Of Liquid:Liquid having low boiling evaporate more quickly e.g. alcohol etc.
Surface Of The Liquid:Rate of evaporation increases with increase in surface area, we spread wet cloths to get them
dry quicker or the unwanted water is spread over larger area of quick evaporation.
Dryness Of Air:Rate of evaporation increases of air is drier. In rainy season the cloth take much time to dry as
rate of evaporation decreases due to moisture in the air.
Speed Of Wind:If speed of wind increases rate of evaporation is also increases. Because the wind carries the
vapor to other place leaving capacity for new vapors. So evaporation increase.
Air Pressure On The Surface If Liquid :If pressure is reduced the rate of evaporation increases. Because lowing of pressure reduces the
boiling point so rate of evaporation increases.
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Chapter-18
ELECTRONICS
Q: Define semi conductors. Give some examples.
Semi Conductors:Those materials which have conductivity between an insulator and a conductor are called
semi conductors. Crystals of germiniun and silicon are the examples of semi conductors.
Q: Define Doping.
Doping:Process by which the electrical conductivity of elements such as Silicon or Germiniun is
increased by adding in them a small amount of an element which has either three or five electrons
in its atom is called doping.
Q: Write two points of differences between n-type substances and p-type substances.
n – type substance p – type substance
If a tetravalent element is dopped with
a pentavalent element four out of five
electron form covalent bonds and the
fifth valence electron is free to move
about which makes the dopped element
a better conductor. Such a material is
known as n – type substance.
If a tetravalent element is dopped with
a trivalent element then three electrons
form covalent bond and a space known
as hole is left. Such a material is known
as P – type substance.
There is an excess of negative electrons.There is an excess of holes. (Positive
changes)
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Q: Write two points of differences between Forward Bias and Reverse Bias.
Forward Bias Reverse Bias
When a semiconductor diode is
connected to a D.C. Source in such a
way that p – side is connected to the
positive terminal and n – side to the
negative terminal and holes move from
the p – type to the n – type and
electrons move from the n – type to the
p – type material across the junction it
is called forward biased.
When a semiconductor diode is
connected to a D.C. Source in such a
way the p – side is connected to the
negative terminal and n – side to the
positive terminal and holes and
electrons move away form the junction
it is called reverse biased.
It has very low electrical resistance. It has very high electrical resistance.
Q: Define rectification. How a PN junction diode is used as a rectifier.
Rectification:The conversion of alternating current (A.C) to direct current (D.C) is called rectification.
Working of Diode as Rectifier:
During the positive half cycle of the A.C. the p – section of diode is positive which make it
forward bias and allow the flow of current through the load ‘R’. But during negative half cycle of
the A.C the p – section of diode is negative which make it reverse bias and stop the flow of current
across the junction. Thus only positive half cycle of the A.C. passes through diode and this
rectification is called half wave rectification.
Q: Define Transistor.
Transistor:
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Transistor is a semiconductor which consists of a thin central layer (3 – 5 µm) of one type
semiconductor material sandwiched between two relatively thick pieces of the other type.
Q: Write the types of transistor.
Types of Transistors:Transistors are of following two types.
1) npn – Transistor
2) pnp – Transistor
npn - Transistor:
The npn transistor has a thin piece of p – type material sandwiched between two pieces of n
– type material.
pnp - Transistor:
The pnp transistor has a thin piece of n – type material sandwiched between two pieces of p
– type material.
Q: How does a transistor works.
Working of Transistors:
A transistor consists of two junctions. One is the emitter base junction (EB) and the other is
collector base (CB). Generally the emitter base junction is forward biased, while the collector base
junction is reverse biased.
As the base emitter junction is forward biased, so its resistance gets very low and a stream
of electrons is injected from the emitter into the base. Thus current begins to flow through this
junction. As the base region is very thin, so practically almost all the electrons injected into the
base are attracted towards the collector due to its large positive potential and very few electrons
enter into the base circuit. In this way a current begins to flow in the collector circuit.
Q: Define amplifier. And how a transistor is used as an amplifier?
Amplifier:An amplifier is a device used to increase the amplitude of an input signal (current or
voltage) without changing the shape of wave.
Working of Transistor as an Amplifier:
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The importance of the transistor is based upon the fact that value of the collector current is
many times greater than the base current. If current is charged slightly, then the collector current
changes significantly. In this way the transistor acts as an amplifier.
Q: What are the advantages of transistor?
Advantages of Transistor:1) Transistors are small in size.
2) Transistors are light in weight.
3) Transistors are not easily broken.
4) Transistors produce little heat.
5) Transistors are very cheap.
6) Transistors use very little potential.
7) Transistors have long operating life.
Q: Define Radar.
Radar:
Radar stands for Radio Detection and Ranging.
Q: How many parts of radar?
Parts of Radar:Radar consists of following parts:
1) Transmitter
2) Receiver
3) Indicating devices
Q: What are the uses of Radar?
Uses of Radar:1) It is used to beware of surrounding ships, ice bergs hidden rocks under water
and hills hidden by mist and cloud.
2) It is used for air traffic control.
3) It helps in navigation in low visibility.
4) It helps to detect enemy planes.
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