Chapter 4 Teacher's Guide

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JPN Pahang Physics Module Form 4

Teachers Guide Chapter 4: Heat

1

4.1 : UNDERSTANDING THERMAL EQUILIBRIUM

By the end of this subtopic, you will be able to

Explain thermal equilibrium Explain how a liquid-in glass thermometer works

1. The net heat will flow from A to B until the temperature of A is the ( same, zero) as thetemperature of B. In this situation, the two bodies are said to have reached thermal

equilibrium.

2. When thermal equilibrium is reached, the net rate of heat flow between the two bodies is(zero, equal)

3. There is no net flow of heat between two objects that are in thermal equilibrium. Twoobjects in thermal equilibrium have the same temperature.

4. The liquid used in glass thermometer should(a)Be easily seen(b)Expand and contract rapidly over a wide range of temperature(c)Not stick to the glass wall of the capillary tube

5. List the characteristic of mercury(a)Opaque liquid(b)Does not stick to the glass(c)Expands uniformly when heated(d)Freezing point -390C(e)Boiling point 3570C

Thermal equilibrium

:Keseimbangan terma

CHAPTER 4: HEAT

Faster. rate of energy transfer

Hot

object

Cold

object

Slower rate of energy transfer

Equivalent to Equivalent to

No net heat transfer

A B


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6. ( Heat, Temperature ) is a form of energy. It flows from a hot body to a cold body.7. The SI unit for ( heat , temperature) is Joule, J.8. ( Heat , Temperature ) is the degree of hotness of a body9. The SI unit for (heat , temperature) is Kelvin, K.10. Lower fixed point (l0 )/ ice point : the temperature of pure melting ice/00C11. Upper fixed point( l100)/steam point: the temperature of steam from water that is boiling

under standard atmospheric pressure /1000C

Exercise 4.1

Section A: Choose the best answer

1. The figure shows two metal blocks.Which the following statement is

false?

A. P and Q are in thermal contactB.P and Q are in thermal

equilibriumC. Energy is transferred from P to QD. Energy is transferred from Q to P

2. When does the energy go when a cupof hot tea cools?

A.It warms the surroundingsB. It warms the water of the teaC. It turns into heat energy and

disappears.

3. Which of the following temperaturecorresponds to zero on the Kelvin

scale?

A. 2730 CB. 00CC. -2730 CD. 1000 C

l0 : length of mercury at ice point

l100 : length of mercury at steam point

l : length of mercury at point

Temperature, =l - l0

l100 - l0x 100

0C


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4. How can the sensitivity of a liquid- inglass thermometer be increased?A. Using a liquid which is a better

conductor of heat

B. Using a capillary tube with anarrower bore.C. Using a longer capillary tube

D. Using a thinner-walked bulb5. Which instrument is most suitable for

measuring a rapidly changingtemperature?

A. Alcohol-in glass thermometerB. ThermocoupleC. Mercury-in-glass thermometer

D. Platinum resistance thermometer6. When shaking hands with Anwar,

Kent Hui noticed that Anwars hand

was cold. However, Anwar felt that

Kent Hui hand was warm. Why didAnwar and Kent Hui not feel the

same sensation?A. Both hands in contact are in

thermal equilibrium.

B.Heat is flowing from Kent Huishand to Anawrs hand

C. Heat is following from Anwarshand to Kent Hui hand.

Section B: Answer all the questions by showing the calculation

1. The length of the mercury column at the ice point and steam point are 5.0 cm and 40.0cmrespectively. When the thermometer is immersed in the liquid P, the length of the mercury

column is 23.0 cm. What is the temperature of the liquid P?

Temperature, = l l0 x 1000C

l100 l0

= 23 5 x 1000C

40 - 5

= 51.430C

2. The length of the mercury column at the steam point and ice point and are 65.0 cm and5.0cm respectively. When the thermometer is immersed in the liquid Q, the length of the

mercury column is 27.0 cm. What is the temperature of the liquid Q?


l100 l0

= 27 5 x 1000C

65 - 5

= 36.670C


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3. The distance between 00C and 1000C is 28.0 cm. When the thermometer is put into abeaker of water, the length of mercury column is 24.5cm above the lower fixed point. What

is the temperature of the water?


l100 l0

= 24.5 x 1000C

28

= 87.50C

4. The distance between 00C and 1000C is 25 cm. When the thermometer is put into a beakerof water, the length of mercury column is 16cm above the lower fixed point. What is the

temperature of the water? What is the length of mercury column from the bulb at

temperatures i) 300C


l100 l0

= 16 x 1000C

25

= 64.00C

Temperature, = l l0 (1000C)

l100 l0

300C = x (100

0C)

25

x = 7.5cm


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SECTION C: Structured Questions

1. Luqman uses an aluminium can, a drinking straw and some plasticine to make a simplethermometer as shown in figure below. He pours a liquid with linear expansion into the

can.

(a)Suggest a kind of liquid that expands linearly. (1m) .

(b)He chooses two fixed points of Celsius scale to calibrate his thermometer. State them.(2m)

(c) If the measurement length of the liquid inside the straw at the temperature of the lowerfixed point and the upper fixed point are 5cm and 16 cm respectively, find the length of

the liquid at 82.50C.

(d)Why should he use a drinking straw of small diameter?

(e)What kind of action should he take if he wants to increase the sensitivity of histhermometer?

Alcohol

82.5 = l- 5 (100)

16 - 5

l = 14.08 cm

Lower fixed point = freezing point of water.

Upper fixed point = boiling point of water

To increases the sensitivity of the thermometer

Use acopper can instead of the aluminium can because it is a better thermal

conductor


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2. What do you mean by heat and temperature?....

4.2 : UNDERSTANDING SPECIFIC HEAT CAPACITYBy the end of this subtopic, you will be able to

Define specific heat capacity (c) State that c = Q/m Determine the specific heat capacity of a liquid Determine the specific heat capacity of a solid Describe applications of specific heat capacity Solve problems involving specific heat capacity

1. Theheat capacity of a body is theamount of heat that must be supplied to the body toincrease its temperature by 1

0C.

2. The heat capacity of an object depends on the(a) .(b) .(c)

3. Thespecific heat capacity of a substance is the amount of heat that must be supplied toincrease the temperature by 1

0Cfor a mass of1 kg of the substance. UnitJkg

-1 0C

-1

4. The heat energy absorbed or given out by an object is given by Q = mc5. High specific heat capacity absorbs a large amount of heat with only asmalltemperature

increase such as plastics.

Heat capacity

Muatan haba

Specific heat capacity

Muatan haba tentu

Temperature of the body

Mass of the bodyType of material

Specific heat capacity , c =Q__

m

Heat is the energy that transfers from one object to another object because of a

temperature difference between them.

Temperature is a measure of degree of hotness of a body.


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6. Conversion of energy

7. Applications of Specific Heat Capacity

Explain the meaning of above application of specific heat capacity:

(a) Water as a coolant in a car engine(i) Water is a good example of substance with a high specific capacity. It is used as a

cooling agent to prevent overheating of the engine .Therefore, water acts as a

heat reservoir as it can absorb a great amount of heat before it boils.

Electrical energy Heat energy

Pt = mc

Heater

Power = P

Electricalenergy

Potentialenergy

Kineticenergy

Object falls from

A high position

Moving object stopped

due to friction

Heat energy

mgh= mc

Heat energy

mv2= mc

Small value of c Big value of cTwo object of

equal mass

Equal rate of

heat supplied

Faster increase

in temperature

Slower increase

in temperature


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(b) Household apparatus and utensils...

...

...

...

(c) Sea breeze

(d) Land breeze

1. A metal has a low specific heat capacity.2. Its temperature increases easily when heated.3. The food or water can be heated faster.4. This is because only a little amount of heat is needed to heat the metal,

therefore more heat is transferred to the food.

5. Examples : pot, frying-pan, filaments of kettles and others utensilsThink about it: Why the handles of utensils made of materials of high c

1. during a day, the land and the sea receive thesame amount of heat from the sun.

2. The land has a lower c, and the temperaturehigher than the sea water.

3. The air above the land to be hotter and flowsup and the cool air from the sea flow

towards the land.

4. The movement of air cause wind to blowfrom the sea and produced a sea breeze.

1. At night, the land and the sea release heat toatmosphere.

2. The sea water has a higher c, and releasemore heat.

3. The air above the sea water to be hotter andflows up and the cool air from the land flow

towards the sea.

4. The movement of air cause wind to blowfrom the land to the sea.


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Exercise 4.2

SECTION A : Choose the best answer

1. The change in the temperature of anobject does not depend on

A.

the mass of the objectB. the type of substance the object ismade of

C.the shape of the objectD. the quantity of heat received

2. Which of the following defines thespecific heat capacity of a substance

correctly?

A. The amount of heat energy requiredto raise the temperature of 1kg of the

substanceB. The amount of heat energy requiredto raise 1kg of the substance by 1

0C.

C. The amount of heat energy requiredto change 1kg of the substance fromthe solid state to the liquid state.

3. Heat energy is supplied at the same rateto 250g of water and 250g of ethanol.

The temperature of the ethanol rises

faster. This is because the ethanol..

A.

is denser than waterB. is less dense than waterC. has a larger specific heat capacity

than water

D.has a smaller specific heat capacitythan water

4. In the experiment to determine thespecific heat capacity of a metal block,

some oil is poured into the holecontaining thermometer. Why is this

done?A. To ensure a better conduction ofheat

B. To reduce the consumption ofelectrical energy

C. To ensure the thermometer is in anupright position.

D. To reduce the friction between thethermometer and the wall of theblock.

SECTION B: Answer all questions by showing the calculation

1. How much heat energy is required to raise the temperature of a 4kg iron bar from 320C to52

0C? (Specific heat capacity of iron = 452 Jkg

-1 0C

-1).

Amount of heat energy required, Q = mc

= 4 x 452 x (52-32)

= 36 160 J

2.

Calculate the amount of heat required to raise the temperature of 0.8 kg of copper from35

0C to 60

0C. (Specific heat capacity of copper = 400 J kg

-1C

-1).

Amount of heat required, Q = mc

= 0.8 x 400 x (60-35)

= 8 000J


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3. Calculate the amount of heat required to raise the temperature of 2.5 kg of water from32

0C to 82

0C. (Specific heat capacity of water = 4200 J kg

-1C

-1).

Amount of heat required, Q = mc

= 2.5 x 4200 x (82-32)

= 525, 000J

4. A 750g aluminium block at 1200C is cooled until 450C. Find the amount of heat isreleased. (Specific heat capacity of aluminium = 900 J kg

-1C

-1).

Amount of heat released, Q = mc

= 0.75 x 900 x (120-45)

= 50 625J

5. 0.2 kg of water at 700C is mixed with 0.6 kg of water at 300C. Assuming that no heat islost, find the final temperature of the mixture. (Specific heat capacity of water = 4200 J

kg-1 C-1)

Amount of heat released, Q = Amount of heat required, Q

mc

= mc

0.2 x 4200 x ( 70- ) = 0.6 x 4200 x ( - 30)

= 400C

SECTION C: Structured questions

1. In figure below, block A of mass 5kg at temperature 1000C is in contact with anotherblock B of mass 2.25kg at temperature 20

0C.

A

B

1000C 200C

5kg

2.25kg


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Assume that there is no energy loss to the surroundings.

(a)Find the final temperature of A and B if they are in thermal equilibrium. Given thespecific heat capacity of A and B are 900 Jkg

-1C

-1and 400 Jkg

-1C

-1respectively.

Amount of heat released by A = Amount of heat absorbed by B

mc(A) = mc(B)

5.0x 900 x ( 100- ) = 2.25 x 400 x (- 20)

= 86.670C

(b)Find the energy given by A during the process.Energy given by A = mc(A)

= 5 x 900 x (100 86.67)

= 59 985 J

(c)Suggest one method to reduce the energy loss to the surroundings...Put them in a sealed polystyrene box.


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4.3 UNDERSTANDING SPECIFIC LATENT HEATBy the end of this subtopic, you will be able to

State that transfer of heat during a change of phase does not cause a change in temperature Define specific latent heat State that l = Q/m Determine the specific latent heat of fusion and specific latent heat of vaporisation Solve problem involving specific latent heat.

1. Four main changes of phase.

2. The heat absorbed or the heat released at constant temperature during a change ofphase is known as latent heat. Q= ml

3. Complete the diagrams below and write a summary of the process.(a) Melting

SolidSolidification

Latent heat released

melting

Latent heatabsorbed

CondensationLatent heat released

Li uid

Gas

Tem erature

Time

.

Solid liquid

P Q

melting

[solid+liquid]

1. From P to Q the temperature does notchange even though heat is still being

absorbed.

2. The temperature is the melting point ofthe substance.

3. The heat absorbed is used for breakingup the bonds of molecules. It is not used

to increase the kinetic energy of the

molecules.

4. At the point P the solid begins to meltand all the solid has melted at point Q.

evaporation

Latent heat absorbed


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(b)Boiling/evaporation

(c) Solidification

(d)Condensation

Tem erature

Time

.

Tem erature

Time

.

Tem erature

Time

.

1. From R to S the temperature does notchange even though heat is still being

absorbed.

2. The temperature is the boiling point ofthe substance.

3. The heat absorbed is used for breakingup the bonds of molecules. It is not used

to increase the kinetic energy of the

molecules.

4. At the point R the liquid begins to boiland all the liquid has boiled at point S.

Liquid gas

R S

boiling[liquid+ gas]


released.2. The temperature as same as the melting

point of the substance and call as freezing

point.

3. The heat released is used for rearrangingthe molecules to form a solid.

4. At the point R the liquid begins to freezeand all the liquid has been solid at point S.

Liquid solid

R S

solidification

[liquid+solid]


released.

2. The temperature as same as the boilingpoint of the substance

3. The heat released is used for rearrangingthe molecules to form a liquid.

4. At the point R the gas begins to condenseand all the gas has been liquid at point S.

gas liquid

R S

condensation

[liquid+ gas]


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4. is the heat absorbed by a melting solid. The specific latentheat of fusion is the quantity of the heat needed to change 1kg of solid to a liquid at its

melting point without any increase in .. The S.I unit of the specific

latent heat of fusion is Jkg-1

.

5. ... is heat of vaporisation is heat absorbed during boiling.The specific latent heat of vaporisation is the quantity of heat needed to change 1kg of

liquid into gas or vapour of its boiling point without any change in ..

The S.I unit is Jkg-1

.

Latent heat of fusion

Latent heat of vaporisation

temperature

temperature

waterice


( melting)

heat lost

( solidification/freezing)

watergas


( boiling)

heat lost

( condensation)


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6. Explain the application of Specific Latent Heat above::

(d) Cooling of beverage

(e) Preservation of Food

(f) Steaming Food

(g) Killing of Germs and Bacteria

When ice melts, its large latent heat is absorbed from surroundings. This property

makes ice a suitable substance for use as a coolant to maintain other substance at a

low temperature. Beverage can be cooled by adding in several cubes of ice. When

the ice melts a large amount of heat (latent heat) is absorbed and this lowers the

temperature of the drink.

The freshness of foodstuff such as fish and meat can be maintained by placing

them in contact with ice. With its large latent heat, ice is able to absorb a large

quantity of heat from the foodstuff as its melts. Thus food can be kept at a low

temperature for an extended period of time.

Food is cooked faster if steamed. When food is steamed, the condensed water

vapour releases a quantity of latent heat and heat capacity. This heat flows to

the food. This is more efficient than boiling the food.

Steam that releases a large quantity of heat is used in the autoclave to kill

germs and bacteria on surgery equipment in hospitals.


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EXERCISE 4.3

Section A:

1. The graph in figure below shows howthe temperature of some wax changes as

it cools from liquid to solid. Whichsection of the graph would the wax be a

mixture of solid and liquid?

A.

PQB. QRC. RSD. ST

2. Figure show a joule meter used formeasuring the electrical energy to melt

some ice in an experiment. To find the

specific latent heat of fusion of ice, whatmust be measured?

A. The time taken for the ice to meltB. The voltage of the electricity supplyC. The mass of water produced by

melting iceD. The temperature change of the ice.

3. It is possible to cook food much fasterwith a pressure cooker as shown above.

Why is it easier to cook food using apressure cooker?

A.

More heat energy can be supplied tothe pressure cookerB. Heat loss from the pressure cooker

can be reduced.

C.Boiling point of water in thepressure cooker is raised

D. Food absorbs more heat energy fromthe high pressure steam

4. Which of the following is not acharacteristic of water that makes itwidely used as a cooling agent?

A. Water is readily availableB. Water does not react with many

other substance

C. Water has a large specific heatcapacity

D. Water has a large density


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5. Figure below shows the experiment setup to determine the specific latent heatof fusion of ice. A control of the

experiment is set up as shown in Figure

(a) with the aim of

A. determining the rate of melting of iceB. ensuring that the ice does not melt

too fast.

C. determining the average value of thespecific latent heat of fusion of ice.

D.determining the mass of ice thatmelts as a result of heat from the

surroundings

6. Scalding of the skin by boiling water isless serious then by steam. This isbecause

A. the boiling point of water is less thanthe temperature of steam

B. the heat of boiling water is quicklylost to the surroundings

C.steam has a high specific latentheat.

D. Steam has a high specific heatcapacity.

SECTION B: Answer the question by showing the calculation

Question 2-7 are based on the following information

Specific heat capacity of water = 4 200 J kg-1 C-1Specific heat capacity of ice = 2 100 J kg-1 C-1Specific latent heat of fusion of ice = 3.36 X 105J kg-1

2. Specific latent heat of vaporization of water = 2.26 X 106 J kg-1300g of ice at 00C melts.How much energy is required for this

Q = ml

= 0.3 x 336 000 kJ kg-1

= 99 000kJ3. An immersion heater rated at 500 W is fitted into a large block of ice at 00C. How long

does it take to melt 1.5kg of ice?

Q = ml

Pt = 1.5 x 3.36 xx 105

500 x t = 501 000


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t = 1008s

4. 300 g of water at 400C is mixed with x g of water at 800C. The final temperature of themixture is 70

0C. Find the value of x

(0.3)(4200)(700-40

0) = x(4200)(80

0-70

0) [Note : Q absorbed by 300 g of water

x = 0.9 kg = Q released by x g of water]

= 900 g

5. Calculate the amount of heat released when 2 kg of ice at 00C is changed into water at0

0C.

Q = mLf

= (2)(336 000) = 672 000 J

6. Calculate the amount of heat needed to convert 3 kg of ice at 00C to water at 300C.Q = mLf+ mc

= (3) (336 000) + (3) (4200) (300)

= 1 386 000 J

7. Find the amount of heat needed to convert 0.5 kg of ice at -150C into steam at 1000CQ = (mc)ice + (mLf)ice + (mc)water + (mLv)steam

= (0.5)(2100)(15) + (0.5)(336 000) + (0.5)(4200)(100) + (0.5)(2260 000)

= 1 523 750 J8. Calculate the amount of heat needed to convert 100 g of ice at 00C into steam at 1000C.

Q = ( mLf)ice + (mc)water + (mLv)steam

= (0.1)(336 000) + (0.1)(4200)(1000) + (0.1)(2260 000)

= 301 600 J

9. The specific latent heat of vaporization of water is 2300 kJ kg-1. How much heat will beabsorbed when 3.2 kg of water is boiled off at its boiling point.

Q = mLv

= (3.2)(2 300 000)

= 7 360 000 J


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4.4 UNDERSTANDING THE GAS LAW

By the end of this subtopic; you will be able to :

Explain gas pressure, temperature and volume in terms of the behaviour of gas molecules. Determine the relationship between

(i) pressure and volume(ii) volume and temperature(iii) pressure and temperature

Explain absolute zero and the absolute/Kelvin scale of temperature Solve problems involving pressure, temperature and volume of a fixed mass of gas

1. Complete the table below.

Property of gas Explanation

Volume,V

m3 The molecules move freely in random motion and fill up the

whole space in the container.

The volume of the gas is equal to the volume of the containerTemperature,T

K (Kelvin) The molecules are in continuous random motion and have anaverage kinetic energy which is proportional to thetemperature.

Pressure,P

Pa(Pascal) The molecules are in continuous random motion. When a molecules collides with the wall of the container and

bounces back, there is a change in momentum and a force is

exerted on the wall

The force per unit area is the pressure of gas

2. The kinetic theory of gas is based on the following assumptions:(a)The molecules in a gas move freely in random motion and posses kinetic energy(b)The force of attraction between the molecules is ignored.


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(c)The collisions of the molecules with each other and with the walls of the container areelastic collisions

4.4.1 Boyles Law

1. Boyles law states that for a fixed mass of gas, the pressure of the gas is inverselyproportional to its volume when the temperature is kept constant.

2. Boyles law can be shown graphically as in Figure above

3. The volume of an air bubble at the base of a sea of 50 m deep is 250cm3. If theatmospheric pressure is 10m of water, find the volume of the air bubble when it reaches

the surface of the sea.

P

V

(a) P inversely proportional to V

0

P

1/V

(b) P directly proportional to 1/V

Small volume

molecules hit wall

more often, greater

pressure

P 1

V

That is PV = constant

Or P1V1 = P2V2

Relationshi between ressure and volume

PI=50m + 10m

V1=250cm3

P2= 10m

P1V1 = P2V2

60m (250 x 10-6

)m3

= 10m x V2

1.5 x 10-3

m3

= V2


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4.4.2 Charless Law

1. Charles law states that for a fixed mass of gas, the volume of the gas is directlyproportional to its absolute temperature when its pressure is kept constant.

2. The temperature -2730C is the lowest possible temperature and is known as the absolutezero of temperature.

3. Fill the table below.Temperature Celsius scale (

0C) Kelvin Scale(K)

Absolute zero -273 0Ice point 0 273

Steam point 100 373

Unknown point ( + 273 )

4. Complete the diagram below.

Relationship between

volume and temperature

Lower temperature

Higher temperature,

faster molecules,

larger volume to keep

the pressure constant

/0C100-273

V T

that is V = constant

T

0

P/Pa


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4.4.3 Pressures Law

1. The pressure law states that for a fixed mass of gas, the pressure of the gas is directlyproportional to its absolute temperature when its volume is kept constant.

EXERSICE 4.4Gas Law

1. A mixture of air and petrol vapour is injected into the cylinder of a car engine when thecylinder volume is 100 cm

3. Its pressure is then 1.0 atm. The valve closes and the mixture is

compressed to 20 cm3. Find the pressure now.

P1V1 = P2V2

(1.0)(100) = P2(20)

P2 = 5.0 atm

2. The volume of an air bubble at the base of a sea of 50 m in deep is 200 cm 3. If theatmospheric pressure is 10 m of water, find the volume of the air bubble when it reaches the

surface of the sea.

P1V1 = P2V2

(50 +10)(200) = (10)V2

V2 = 1200 cm3

P TThat is P = constant

T

Relationship between

pressure and temperature

Higher

temperature

molecules move

faster, greater

pressure


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3. The volume of an air bubble is 5 mm3 when it is at a depth of h m below the water surface.Given that its volume is 15 mm

3when it is at a depth of 2 m, find the value of h.

(Atmospheric pressure = 10 m of water)

P1V1 = P2V2

(h + 10)(5) = (2 + 10)(15)

5h + 50 = 180

h = 26 m

4. An air bubble has a volume of V cm3 when it is released at a depth of 45m from the watersurface. Find its volume (V) when it reaches the water surface. (Atmospheric pressure = 10

m of water)

P1V1 = P2V2

(45 + 10)(V) = (10)(V2)

V2 = 5.5 V cm3

5. A gas of volume 20m3 at 370C is heated until its temperature becomes 870C at constantpressure. What is the increase in volume?

V1 = V2 , 20 = V2 .

T1 T2 370

+ 273 870

+ 273

V2 = 23.23 m3

6. The air pressure in a container at 330C is 1.4 X 1O5 N m-2. The container is heated until thetemperature is 55

0C. What is the final air pressure if the volume of the container is fixed?

P1 = P2 , 1.4 x 105

= P2 .

T1 T2 330

+ 273 550

+ 273

P2 = 1.5 x 105

N m-2


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7. The volume of a gas is 1 cm3 at 150C. The gas is heated at fixed pressure until the volumebecomes triple the initial volume. Calculate the final temperature of the gas.

V1 = V2 , 1 = 3 .

T1 T2 150

+ 273 T2

T2 =864K

T2 =2 + 273

2 = T2 273

= 864 - 273

2 = 5910C

8. An enclosed container contains a fixed mass of gas at 250C and at the atmospheric pressure.The container is heated and temperature of the gas increases to 980C. Find the new pressure

of the gas if the volume of the container is constant.(Atmospheric pressure = 1.0 X 105N

rn2)

P1 = P2 , 1.0 x 105

= P2 .

T1 T2 250

+ 273 980

+ 273

P2 = 1.24 x 105

N m2

9. The pressure of a gas decreases from 1.2 x 105 Pa to 9 x 105 Pa at 400C. If the volume of thegas is constant, find the initial temperature of the gas.

P1 = P2 , 1.2 x 105

= 9 x 105

.

T1 T2 1 + 273 400

+ 273

1 = -231.30C

= 41.7K


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PART A: CHAPTER 4

1. A 5kg iron sphere of temperature500C is put in contact with a 1kgcopper sphere of temperature 273K

and they are put inside an insulated

box. Which of the following

statements is correct when they reachthermal equilibrium?

D. A iron sphere will have atemperature of 273K

E. The copper sphere will have atemperature of 50

0C.

F. Both spheres have the sametemperature.

G. The temperature of the ironsphere will be lower than 50

0C

2. In the process to transfer heat fromone object to another object, which

of the following processes does notinvolve a transfer to material?

A. ConvectionB. VaporisationC. RadiationD. Evaporation

3. When we use a microwave oven toheat up some food in a lunch box, we

should open the lid slightly. Which

of the following explanations iscorrect?

A. To allow microwave to go insidethe lunch box

B. To allow the water vapours to goout, otherwise the box will

explodeC. To allow microwave to reflect

more times inside the lunch box

D. To allow microwave to penetratedeeper into the lunch box.

4. Water is generally used to put outfire. Which of the following

explanation is not correct?

A. Water has a high specific heatcapacity

B. Steam can cut off the supply ofoxygen

C. Water is easily availableD. Water can react with some

material

5. Given that the heat capacity of acertain sample is 5000 J

0C

-1. Which

of the following is correct?A. The mass of this sample is 1kg.B. The energy needed to increase

the temperature of 1 kg of this

sample is 5000 J.C. The energy needed to increase

the temperature of 0.5kg of this

sample is 2500J.D. The temperature of this sample

will increase 10

C when 5 000 Jenergy is absorbed by thissample.

6. Which of the following statement iscorrect?A. The total mass of the object is

kept constant when fusion

occurs.B. The internal energy of the object

is increased when condensation

occursC. Energy is absorbed when

condensation occurs.

D. Energy is absorbed whenvaporization occurs.


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7. Water molecules change their statesbetween the liquid and gaseous states

A. only when water vapour issaturatedB. at all times because evaporationand condensation occur any time

C. only when the vapour moleculesproduce a pressure as the same as

the atmospheric pressureD. only when the water is boiling

8. Based on the kinetic theory of gaswhich one of the following does notexplain the behaviour of gas

molecules in a container?A. Gas molecules move randomlyB. Gas molecules collide elastically

with the walls of the container

C. Gas molecules move faster astemperature increases

D. Gas molecules collideinelastically with each other

9. A cylinder which contains gas iscompressed at constant temperature

of the gas increase because

A. the average speed of gasmolecules increases

B. the number of gas moleculesincreases

C. the average distance between thegas molecules increasesD. the rate of collision between thegas molecules and the wallsincreases

10. A plastic bag is filled with air. It isimmersed in the boiling water as

shown in diagram below.

Which of the following statements is

false?

A. The volume of the plastic bagincreases.

B. The pressure of air moleculesincreases

C. The air molecules in the bagmove faster

D. The repulsive force of boilingwater slows down the movementof air molecule


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PART B;

1. A research student wishes to carry out an investigation on the temperature change of thesubstance in the temperature range -50

0C to 50

0C. The instrument used to measure the

temperature is a liquid in glass thermometer.

Table 1

(a) (i) State the principle used in a liquid- in glass thermometer.(1m)........................................................................................................................................

(ii)Briefly explain the principle stated in (a)(i) (3m).

.

.

(b) Table 1 shows the characteristic of 4 types of thermometer: A,B C and D. On the basisof the information given in Table 1, explain the characteristics of, and suggest a suitable

thermometer for the experiment.(5 m)

..

Thermometer A B C D

Liquid Mercury Mercury Alcohol Alcohol

Freezing point of liquid (0C) -39 -39 -112 -112

Boiling point of liquid (0C) 360 360 360 360

Diameter of capillary tube Large Small Large Small

Cross section

Principle of thermal equilibrium

A system is in a state of thermal equilibrium if the net rate of heat flow

between the components of the system is zero. This means that the components

of the system are at the same temperature

Alcohol freezing point is less than -50C, boiling point higher than 50C.Thus the

alcohol will not boil.

Capillary tube has small diameter will produce a large change in the length thus

making the change clearly visible.

Small diameter increases sensitivity of the thermometer


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(b) the rate of heat supplied to the waterRate of heat supplied to the water = 12 600J

120s

= 105 Js-1

(c) the specific heat capacity of the metal block PHeat supplied by metal block P = heat gained by water

0.500 x c x(100 -42) = 12 600J

c = 434 J kg-1

C-1

3. A student performs an experiment to investigate the energy change in a system. Heprepares a cardboard tube 50.0 cm long closed by a stopper at one end. Lead shot of

mass 500 g is placed in the tube and the other end of the tube is also closed by a stopper.

The height of the lead shot in the tube is 5.0 cm as shown in Figure 3.1. The student then

holds both ends of the tube and inverts it 100 times (Figure 3.2).

(a)State the energy change each time the tube is inverted...

..

(b)What is the average distance taken by the lead shot each time the tube is inverted?45.0 cm

Figure 3.1 Figure 3.2

Gravitational potential energy kinetic energy heat energy


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Figure (a) Figure (b)

(c)Calculate the time taken by the lead shot to fall from the top to the bottom of the tube.S = ut + at

2

0.45 = 0 + (10)t2

t = 0.3s

(d)After inverting the tube 100 times, the temperature of the lead shot is found to haveincreased by 30C.

i. Calculate the work done on the lead shot.Work done = (100) mgh

= 100 x 0.500 x 10 x 0.45

= 225 J

ii. Calculate the specific heat capacity of lead.mc = 225 J

c = 225

(0.500 x 3)

= 150 Jkg-1

C-1

iii. State the assumption used in your calculation in (d)ii....

.

PART C: EXPERIMENT

1. Before travelling on a long journey, Luqman measured the air pressure the tyre of his caras shown in Figure (a) He found that the air pressure of the tyre was 200 kPa. After the

journey, Luqman measured again the air pressure of the tyre as shown in Figure (b) He

found that the air pressure had increase to 245 kPa. Luqman also found that the tyre was

hotter after the journey although the size of the tyre did not change.

Using the information provided by Luqman and his observations on air pressure in the

tyre of his car:

No heat loss to the surroundings/All the gravitational potential energy is

converted into heat energy


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Choose

suitable apparatus such as pressure gauge, a round-bottomed flask and any other

apparatus that may he necessary. In your description, state clearly the following:

i. Aim of the experiment,

ii. Variables in the experiment,

iii. List of apparatus and materials,

iv. Arrangement of the apparatus,

v. The procedure of the experiment including the method of controlling themanipulated variable and the method of measuring the responding variable,

vi. The way you would tabulate the data,vii. The way you would analyse the data. [10 marks]

(a)State one suitable inference that can be made. [1 mark](b)State appropriate hypothesis for an investigation. [1 mark](c)Design an experiment to investigate the hypothesis stated in (b).


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Inference At constant volume, the air pressure depends on the temperature

Hypothesis At constant volume, the air pressure increase as the temperature

increases

Aim To investigate the relationship between the air pressure and the

temperature at constant volume.

Variable Constant variable :Air temperature

Manipulate variable :Air pressure

Responding variable : Volume of air

Material and Apparatus Round-bottom flask, rubber tube, Bourdon gauge, beaker,

stirrer, thermometer, wire gauze, tripod stand and Bunsen

burner.

Arrangement of

apparatus

Procedure The apparatus is set up as shown in the diagram above. The beaker is filled with ice-cold water until the flask is

completely immersed.

The water is stirred and the initial temperature readingtaken. The pressure reading from the bourdon gauge is also

taken.

The water is heated and constant stirred. When the watertemperature increases by 100C, the Bunsen burner is

removed and the stirring of water is continued. The

temperature and pressure readings of the trapped air are

recorded in the table


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The above procedure is repeated until the water temperaturealmost reaches boiling point.

Tabulation of Data

Analysis of Data

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Chapter 4 Teacher's Guide