physics form 4 chapter 4

7/28/2019 Physics Form 4 Chapter 4

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JPN Pahang Physics Module Form 4

Students Copy Chapter 4: Heat

86

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 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

..

.

..

..

.

.

.

.

.. rate of energy transfer

Hot

object

Cold

object

.. 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 4.1Section 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

4. How can the sensitivity of a liquid- inglass thermometer be increased?

..

l0 : length of mercury at ice point

l100 : length of mercury at steam pointl : length of mercury at point

Temperature, =l - l0

l100 - l0x 100 C


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A. Using a liquid which is a betterconductor of heat

B. Using a capillary tube with anarrower bore.

C. Using a longer capillary tubeD.

Using a thinner-walked bulb

5. Which instrument is most suitable formeasuring a rapidly changing

temperature?A. Alcohol-inglass thermometerB. ThermocoupleC. Mercury-in-glass thermometerD. Platinum resistance thermometer

6. When shaking hands with Anwar,Kent Hui niticed that Anwars handwas cold. However, Anwar felt that

Kent Hui hand was warm. Why did

Anwar and Kent Hui not feel thesame 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?

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?

Temperature, = ll0 x 1000C

l100l0

= 275 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?

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


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3

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?


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4

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

: UNDERSTANDING SPECIFIC HEAT CAPACITY

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

Define specific heat capacity State that c = Q/MC 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. The .. of a body is the .. that must be supplied to thebody to increase its temperature by 1

0C.

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

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

0C for a mass of 1 kg of the substance. Unit Jkg

-1K

-1

4. The heat energy absorbed or given out by an object is given by Q = mcO.5. High specific heat capacity absorb a large amount of heat with only a

temperature increase such as plastics.

Heat capacity

Muatan haba

Specific heat capacity

Muatan haba tentu

Specific heat capacity , c =Q__

m


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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) ....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

Electrical energy Heat energy

Pt = mc

Heater

Power = P

energy

..energy

..energy

Object falls from

A hi h osition

Moving object stopped

due to friction

Heat energymgh= mc

Heat energy

mv2= mc

Small value of c Big value of cTwo object of

equal mass

Equal rate of

heat supplied

.

increase in

tem erature

.

increase in

tem erature


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(b) Household apparatus and utensils...

...

...

...

(c) Sea breeze

(d) Land breeze


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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

substance

B.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 from

the 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 risesfaster. 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 of heatB. To reduce the consumption of

electrical energy

C. To ensure the thermometer is in anupright position.

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

block.

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 32 0C to52

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

-1 0C

-1).


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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).

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).

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

-1C

-1).

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

)


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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.

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.

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

(c)Suggest one method to reduce the energy loss to the surroundings...

A

B

100 C 20 C

5kg

2.25kg


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89

UNDERSTANDING SPECIFIC LATENT HEAT

By the 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 summarized.(a) Melting

SolidSolidification

Latent heat

BoilingLatent heat . Condensation

Latent heat

Li uid

Gas

Tem erature

Time

.


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(b)Boiling

(c) Solidification

(d)Condensation

Tem erature

Time

.

Tem erature

Time

.

Tem erature

Time

.


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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

.

waterice

watergas


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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


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93

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 amixture of solid and liquid?

A.

PQB. QRC. RSD. ST

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

some ice in an experiment. To find thespecific latent heat of fusion of ice, what

must be measured?

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

melting ice

D. 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 cooker

B. Heat loss from the pressure cookercan be reduced.

C. Boiling point of water in the pressurecooker is raised

D. Food absorbs more heat energy fromthe high pressure steam

4. Which of the following is not acharacteristics 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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2

5. Figure below shows the experiment setup to determine the specific latent heat

of fusion of ice. A control of theexperiment 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 the

specific latent heat of fusion of ice.

D.

determining the mass of ice thatmelts as a result of heat from thesurroundings

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

because

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 latent heat.D. Steam has a high specific heatcapacity.

SECTION B: Answer the question by showing the calculation

1. 300g of ice at 00C melts. How much energy is required for this

Question 2-7 are based on the following information

Specific heat capacity of water = 4 200 J kg-1 C-1 Specific heat capacity of ice = 2 100 J kg-1 C-1 Specific latent heat of fusion of ice = 3.34 X 105J kg-1 Specific latent heat of vaporization of water = 2.26 X 106 J kg-1

2.

An immersion heater rated at 500 W is fitted into a large block of ice at 0

0

C. How longdoes it take to melt 1.5kg of ice?


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3. 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

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

0C.

5. Calculate the amount of heat needed to convert 3 kg of ice at 00C to water at 300C.

6. Find the amount of heat needed to convert 0.5 kg of ice at150C into steam at 1000C

7. Calculate the amount of heat needed to convert 100 g of ice at 00C into steam at 1000C.

8. 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.


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3

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

Temperature,T

K (Kelvin)

Pressure,P

Pa(Pascal)

2. The kinetic theory of gas is based on the following assumptions:................................................................................................................................................

................................................................................................................................................

................................................................................................................................................

................................................................................................................................................


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4.4.1 Boyles Law

1. Boyles law states that..... ..........................................................................

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

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


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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.

4.4.2 Charless Law

1. Charles law states .

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

temperature.

Relationship between

volume and temperature

Lower temperature

Higher temperature,faster molecules,

larger volume to keepthe pressure constant

V T

that is V = constant

T

PI=50m + 10m

V1=250cm3

P2= 10m


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2. Fill the table below.Temperature Celsius scale (

0C) Kelvin Scale(K)

Absolute zero

Ice point

Steam point

Unknown point

3. Complete the diagram below.

4.4.3 Pressures Law

1. The pressure law states ......

/0C100-273

P TThat is P = constant

T

Relationship between

pressure and temperature

Higher

temperature

molecules move

faster, greater

pressure


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EXERSICE 4.4:Gas Law

1. A mixture of air and petrol vapour is injected into the cylinder of a car engine when thecylinder volume is 100 cm3. Its pressure is then 1.0 atm. The valve closes and the mixture is

compressed to 20 cm3. Find the pressure now.

2. The volume of an air bubble at the base of a sea of 50 in deep is 200 cm3. If the atmosphericpressure is 10 in of water, find the volume of the air bubble when it reaches the surface of

the sea.

3. The volume of an air bubble is 5 mm3 when it is at a depth of h in below the water surface.Given that its volume is 15 mm3 when it is at a depth of 2 in, find the value of h.

(Atmospheric pressure = 10 m of water)


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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)

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

6. The air pressure in a container at 330C is 1.4 X 1O5 N m2. The container is heated until thetemperature is 55

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

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.


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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 98

0C. Find the new pressure

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

rn2)

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.


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PART A: CHAPTER 4

1. A 5kg iron sphere of temperature50

0C is put in contact with a 1kg

copper sphere of temperature 273Kand they are put inside an insulatedbox. Which of the following

statements is correct when they reach

thermal equilibrium?D. A iron sphere will have a

temperature of 273K

E. The copper sphere will have atemperature of 50

0C.

F. Both the sphere have the sametemperature.

G.

The temperature of the ironsphere will be lower than 500C

2. In the process to transfer heat fromone object to another object, whichof the following processes does not

involve 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. Whichof the following explanations is

correct?

A. To allow microwave to go insidethe lunch box

B. To allow the water vapors 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 10C when 5 000 J

energy is absorbed by this

sample.

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

occurs

C. Energy is absorbed whencondensation 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 issaturated

B. at all times because evaporationand condensation occur any timeC. only when the vapour moleculesproduce a pressure as the same as

the atmospheric pressure

D. only when the water is boiling8. Based on the kinetic theory of gas

which one of the following does not

explain the behaviour of gasmolecules in a container?

A. Gas molecules move randomlyB.

Gas molecules collide elasticallywith 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 increases

D. the rate of collision between thegas molecules and the wallsincreases

10. A plastic bag is filled with air. It isimmersed in the boiling water asshown in diagram below.

Which of the following statements isfalse?

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 movement

of 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- inglass 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


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(c) The length of the mercury column in uncalibrated thermometer is 6.0cm and 18.5 cm at0

0C and 100

0C. respectively. When the thermometer is placed in a liquid, the length of

the mercury column is 14.0cm

(i) Calculate the temperature of the liquid

(ii) State two thermometric properties which can be used to calibrate a thermometer. (6m)

2. A metal block P of mass 500 g is heated is boiling water at a temperature of 1000C.Block P is then transferred into the water at a temperature of 300C in a polystyrene cup.

The mass of water in the polystyrene cup is 250 g. After 2 minutes, the water temperature

rises to 420C.

Assuming that the heat absorbed by the polystyrene cup and heat loss to the

surroundings are negligible.{Specific heat capacity of water 4 200 j kg-1

C-1

)

Calculate

(a) the quantity of heat gained by water the polystyrene cup

Figure 2


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(b) the rate of heat supplied to the water

(c) the specific heat capacity of the metal block P

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?

Figure 3.1 Figure 3.2


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(c)Calculate the time taken by the lead shot to fall from the top to the bottom of the tube.

(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.

ii. Calculate the specific heat capacity of lead.

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:

Figure (a) Figure (b)


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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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physics form 4 chapter 4

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