wb1a_test

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© Oxford University Press 2003

Name: Date:

Multiple-choiceTest: Heat

New Physics at Work58

Unless otherwise specified, take:specific heat capacity of water = 4200 J kg–1 ° C–1,specific latent heat of fusion of ice = 3.34 × 105 J kg–1,specific latent heat of vaporization of water = 2.26 × 106 J kg–1

Section A: Core

1 Room temperature is nearest to

A 0 ° C.

B 20 ° C.

C 55 ° C.

D 100 ° C.

2 Which of the following statements about heat iscorrect?

A Heat is the energy stored in a body.

B Heat is the temperature of a body.

C Heat is the energy transferred dueto temperature difference betweentwo bodies.

D The unit of heat is watt(W).

3 The apparatus in Figure a is used to measurethe specific heat capacity of a liquid. Which ofthe following can be done to improve theaccuracy of the experiment?

(1) Taking the final temperature of the liquidimmediately after switching off the powersupply.

C

B

(2) Covering the cup with a lid.

(3) Totally immerse the heater into the liquid.

A (1) only.

B (1) and (3) only.

C (2) and (3) only.

D (1), (2) and (3).

4 It takes 12 s for a 200 W heater to raise thetemperature of a liquid of 1 kg by 1 ° C. Whichof the following statement(s) is/are correct?

(1) It takes one minute to raise thetemperature of the liquid by 5 ° C.

(2) The specific heat capacity of the liquid is2400 J kg–1 ° C–1.

(3) If the mass of the liquid were 2 kg, a 400 W heater should be used if we want toraise the temperature of it by 1 ° C in 6 s.

A (1) only.

B (1) and (2) only.

C (2) and (3) only.

D (1), (2) and (3).

5 Which of the following energy transferprocesses involves a transfer of matter?

A Conduction

B Convection

C Radiation

D None of the above.

6 Which of the following statements about heatradiation is incorrect?

A Very hot objects such as tungstenfilaments only emit visible lightbut no infra-red radiation.

B The Sun transmits energy to theEarth mainly by radiation.

C Blackened surfaces emit moreradiation than shiny surfaces.

D Wearing black clothes can keepwarm by absorbing more radiation.

A

B

B

C

Test: Heat

thermometer

to powersupply

heater

liquid

Fig a


Class: Name: Date: Test: Heat

New Physics at Work 59

7

Which of the surfaces in Figure b is best at:

absorbing emitting reflecting heat heat heatradiation radiation radiation

A white white silvery

B white silvery dull black

C dull black white white

D dull black dull black silvery

8

Figure c shows a lighted candle. Positions Pand Q are equidistant from the flame. You willfeel hotter at P than at Q mainly because

A there is no infra-red radiation inthe horizontal direction.

B energy is transferred byconduction more efficiently inthe vertical direction.

C the light intensity at P is higherthan that at Q.

D hot air rises up and transfers more energy to position P.

D

D

9 A 0.1-kg ice cube at 0 ° C is dropped into 1 kgof water at 60 ° C. Assume that there is noheat loss to the surroundings. What is thefinal temperature of the mixture?

A 46.7 ° C

B 47.3 ° C

C 52.3 ° C

D 54.5 ° C

10 Which of the following is the mathematicaldescription of the statement ‘the energyneeded to raise the temperature of 1 kg of asubstance through 1 ° C?

A E = Pt

B E = mc ∆ T

C E = ml

D E = c ∆ T

11 If an immersion heater takes 5 minutes tobring a cup of water to 100 ° C from 60 ° C,how much extra time is required to vaporizeall the water completely? Neglect energy lostto surroundings.

A 26.9 minutes

B 44.8 minutes

C 67.3 minutes

D Cannot be determined since mass of the cup of water is unknown.

C

B

B

white dull black silvery

Fig b

P x

Q x

Fig c

Class:


Name: Date:


Section B: Core + Extension

12 Which of the following statements aboutinternal energy, conduction and convectionis/are true?

(1) The internal energy of a body is ameasure of the total kinetic energy andpotential energy of the particles in thebody.

(2) In heating a solid by conduction, energyis transferred as a result of particlevibrations.

(3) When water is heated, convection currentis formed as a result of the difference indensity of water at different parts.

A (1) only.

B (2) only.

C (2) and (3) only.

D (1), (2) and (3).

13 When a solid is melting, which of thefollowing statements is/are correct?

(1) The average potential energy of theparticles remains unchanged.

(2) The average separation between theparticles is increased.

(3) The average kinetic energy of theparticles remains unchanged.

A (1) only.

B (2) only.

C (2) and (3) only.

D (1), (2) and (3).C

D

14 Two solids X and Y of identical mass areheated separately. The graphs below show thevariation of their temperatures with time.Heating stops when they attain the finaltemperature T1.

Fig d

Which of the following statements is/arecorrect?

(1) The specific latent heat of fusion of X islarger than that of Y.

(2) When both are in liquid state, the specificheat capacity of X is larger than that of Y.

(3) When heating stops, the average KE ofthe molecules of the 2 substances areabout the same.

A (1) only.

B (2) only.

C (2) and (3) only.

D (1), (2) and (3).C

temperature / ° C

T1

T0

time / s

X Y

Test: Heat

E

E

E



ConventionalTest: Heat


Section A: Core

1 Figure a shows an engine cooling system. Water (at 25 ° C) takes in energy from thehot engine and carries it to the radiator where it is released into the air. Normally, thewater enters the radiator at 75 ° C. There is 5 kg of water in the engine cooling system.

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(a) The flow rate of water is 2 kg s–1. Find the energy absorbed by the water in onesecond.(Note: specific heat capacity of water = 4200 J kg–1 ° C–1)

(2 marks)

Energy absorbed = mc ∆ T (1M)

= 2 (4200)(75 – 25)

= 4.2 × 105 J (1A)

(b) The radiator becomes faulty and stops functioning. The engine gets overheatedand all water (at 75 ° C) is heated to boil. Steam (at 100 ° C) leaks from the joints ofthe engine. Calculate the energy absorbed by the water when all of it boils away.

(2 marks)

Energy absorbed = mc ∆ T + ml (1M)

= 5 (4200)(100 – 75) + 5 (2.26 × 106)

= 1.18 × 107 J (1A)

(c) Suggest TWO reasons why water is regarded as an excellent cooling agent.(2 marks)

Water has high specific heat capacity.

Water is very cheap.

Water can be obtained easily.

Any two of the above. (1A + 1A)

heat given outby radiator heat removed

om engine75 ° C

25 ° C

pumpFig a

Class:


Name: Date:


Section B: Core + Extension

2 An experiment is performed to investigate the rate of energy loss of hot water indifferent circumstances. Three identical flasks containing the same amount of hotwater at 80 ° C is put into 3 different plastic boxes (Fig b).

Test: Heat

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*

cork

box B

water

air silvery wall

cork

box C

water

vacuum silvery wall

cork

box A

water

air

Fig b

After 15 minutes, the final temperature of the water is measured again:

Temperature of water before Temperature of water after the experiment the experiment

Box A 80 ° C 48 ° C

Box B 80 ° C 62 ° C

Box C 80 ° C 72 ° C

Explain why there are such differences in temperature readings in the 3 set-ups.(5 marks)

The water in the three boxes loses energy by radiation. (1A)

In box B and box C, the silvery walls reflect part of the radiation (1A)

and the water absorbs some of the reflected radiation again. (1A)

Therefore, the water in box A loses energy most rapidly.

Besides, there is no air in box C to conduct energy away from the water. (1A)

The water in box C loses energy most slowly.

For effective communication (1C)




3 Figure c shows a simplified domestic air-conditioning system. A liquid called therefrigerant evaporates inside the pipe on side A. The vapour formed is then pumpedto the heat exchanger in side B where it condenses and returns to side A again. Page total

liquid

vapourvapour pump

insulating matA B

Fig c

fans

Fig d

(a) (i) Which side (A or B) of the pipe is cooled by this process? Explain brieflyhow it is cooled. (2 marks)

(ii) What are the changes in the particles of the refrigerant in the pipe on side Aduring this process? (2 marks)

(b) Explain why the pipe on side A and B is not straight. (2 marks)

(c) Two electric fans (Fig d) are usually installed in the air-conditioner. Sketch inFigure c to show where they should be placed. (2 marks)

(a) (i) The pipe in side A is cooled by this process. (1A)

When the refrigerant evaporates, it absorbs latent heat of vaporization from the coil. (1A)

(a) (ii) The average separation (1A)

and hence the potential energy between the molecules increases. (1A)

(b) To increase the surface area (1A)

on which air can exchange heat with the pipe more efficiently. (1A)

(c) One electric fan on the left of the insulating mat, blowing air to the left. (1A)

One electric fan on the right of the insulating mat, blowing air to the right. (1A)

E

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