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Secondary 4 Pure Physics Thermal Physics Quiz
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Questions
Secondary 4 Pure Physics Quiz - Thermal Physics
Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ________ / 40
Duration: 50 minutes
Total Marks: 40
Instructions:
- Answer ALL questions.
- Show all working clearly for calculation questions. Marks are awarded for correct method even if the final answer is wrong.
- Write your answers in the spaces provided.
- The number of marks for each question or part-question is shown in brackets [ ].
- You may use a calculator where appropriate.
- Assume the specific heat capacity of water is 4.2 J/(g·°C) unless otherwise stated.
Section A: Multiple Choice (Questions 1–5) [10 marks]
For each question, choose the most correct answer (A, B, C, or D) and write the letter in the space provided.
1. Which of the following best describes the process of thermal conduction?
A. Transfer of thermal energy by the bulk movement of a fluid
B. Transfer of thermal energy by electromagnetic waves
C. Transfer of thermal energy through a material without the material itself moving
D. Transfer of thermal energy only in gases and liquids
Answer: ________ [1]
2. A metal rod is heated at one end. After some time, the other end also becomes warm. Which statement best explains this observation?
A. Hot molecules at the heated end travel along the rod to the cold end.
B. Free electrons transfer kinetic energy along the rod by colliding with other particles.
C. The heated end expands and pushes the cold end, making it warm.
D. Radiation from the heated end travels through the rod to the cold end.
Answer: ________ [1]
3. A 200 g block of aluminium (specific heat capacity = 900 J/(kg·°C)) is heated from 25 °C to 75 °C. How much thermal energy is absorbed by the block?
A. 4 500 J
B. 9 000 J
C. 13 500 J
D. 18 000 J
Answer: ________ [1]
4. Which of the following surfaces would be the best absorber of infrared radiation?
A. Shiny silver
B. White and smooth
C. Black and matt
D. Transparent glass
Answer: ________ [1]
5. A beaker of hot water is left to cool in a room. Which of the following graphs best shows how the temperature of the water changes with time?
A. A straight line sloping downwards
B. A curve that starts steep and gradually becomes less steep
C. A horizontal line
D. A curve that starts flat and gradually becomes steeper
Answer: ________ [1]
Section B: Short-Answer and Structured Questions (Questions 6–10) [10 marks]
6. Define the following terms:
(a) Specific heat capacity: ____________________________________________________________
________________________________________________________________________________ [1]
(b) Thermal equilibrium: ____________________________________________________________
________________________________________________________________________________ [1]
7. State two differences between boiling and evaporation.
- _______________________________________________________________________________ [1]
- _______________________________________________________________________________ [1]
8. Explain, in terms of molecular motion, why the pressure of a gas inside a sealed container increases when the temperature is raised.
________________________________________________________________________________ [2]
9. A student heats 500 g of water using an electric heater. The temperature of the water rises from 20 °C to 80 °C in 10 minutes.
(a) Calculate the thermal energy absorbed by the water.
(Use specific heat capacity of water = 4 200 J/(kg·°C))
Working: ______________________________________________________________________
Answer: ________________________ [2]
(b) Calculate the power of the heater, assuming no energy is lost to the surroundings.
Working: ______________________________________________________________________
Answer: ________________________ [2]
10. A copper rod and a glass rod of the same dimensions are each held over a Bunsen flame at one end. After 30 seconds, the far end of the copper rod is too hot to touch, while the far end of the glass rod remains cool.
Explain this observation in terms of thermal conductivity.
________________________________________________________________________________ [2]
Section C: Short-Answer and Structured Questions (Questions 11–15) [10 marks]
11. State one everyday application each of:
(a) Good thermal conductor: _________________________________________________________ [1]
(b) Good thermal insulator: _________________________________________________________ [1]
12. A 0.8 kg iron block at 150 °C is dropped into 1.2 kg of water at 25 °C inside a container of negligible heat capacity. The final steady temperature of the mixture is 32 °C.
(a) Calculate the thermal energy lost by the iron block.
(Use specific heat capacity of iron = 450 J/(kg·°C))
Working: ______________________________________________________________________
Answer: ________________________ [2]
(b) Using your answer to (a), calculate the thermal energy gained by the water.
Answer: ________________________ [1]
(c) Comment on whether your answers to (a) and (b) are consistent with the principle of conservation of energy. Suggest a reason for any discrepancy.
________________________________________________________________________________ [1]
13. Explain why a car parked in direct sunlight on a hot day becomes very hot inside, even though the windows are closed. Refer to at least two mechanisms of heat transfer in your answer.
________________________________________________________________________________ [3]
14. A thermometer is placed in a mixture of ice and water at 0 °C. The thermometer reads 0 °C. The mixture is then heated until all the ice has melted and the water reaches 20 °C.
(a) Explain why the temperature remains at 0 °C while the ice is melting.
________________________________________________________________________________ [1]
(b) State what happens to the internal energy of the water as its temperature rises from 0 °C to 20 °C.
________________________________________________________________________________ [1]
15. A shiny metal teapot and a black ceramic teapot of the same size are both filled with boiling water at 100 °C and left to cool in the same room.
(a) Which teapot will cool faster? ____________________________________________________ [1]
(b) Explain your answer to (a) with reference to infrared radiation.
________________________________________________________________________________ [1]
Section D: Application and Data-Response Questions (Questions 16–20) [10 marks]
16. A student investigates the rate of cooling of hot water in two identical beakers. Beaker A is wrapped with aluminium foil on the outside. Beaker B is left unwrapped. Both beakers contain the same volume of hot water at the same initial temperature and are placed in the same room.
(a) Predict which beaker will cool more slowly. Explain your answer.
________________________________________________________________________________ [2]
(b) State one variable that must be kept constant in this experiment to ensure a fair test.
________________________________________________________________________________ [1]
(c) Sketch on the axes below the expected temperature–time graph for both beakers on the same set of axes. Label your curves A and B.
Temperature / °C
|
|_________________________________ Time / min
[2]
17. The table below shows the specific heat capacities of four substances.
| Substance | Specific Heat Capacity / (J/(kg·°C)) |
|---|---|
| Water | 4 200 |
| Aluminium | 900 |
| Copper | 385 |
| Iron | 450 |
(a) Calculate the thermal energy required to heat 0.5 kg of an unknown liquid from 20 °C to 100 °C, given that the specific heat capacity of the liquid is 2 100 J/(kg·°C).
Working: ______________________________________________________________________
Answer: ________________________ [2]
(b) A 0.5 kg sample of a substance absorbs 168 000 J of thermal energy when heated from 20 °C to 100 °C. Using the table above, identify the substance.
Working: ______________________________________________________________________
Answer: ________________________ [2]
(c) Compare the specific heat capacity of the unknown liquid in (a) with that of water.
________________________________________________________________________________ [1]
18. A vacuum flask is designed to keep hot liquids hot and cold liquids cold.
(a) Explain how the vacuum between the double walls reduces heat transfer.
________________________________________________________________________________ [1]
(b) Explain how the silvered surfaces on the inner walls reduce heat transfer.
________________________________________________________________________________ [1]
(c) State one other design feature of a vacuum flask that reduces heat transfer and explain how it works.
________________________________________________________________________________ [1]
19. A solar heater uses a copper plate with a mass of 2.0 kg to absorb energy from the Sun. The temperature of the copper plate rises from 25 °C to 85 °C over a period of 5 minutes.
(Use specific heat capacity of copper = 385 J/(kg·°C).)
(a) Calculate the thermal energy absorbed by the copper plate.
Working: ______________________________________________________________________
Answer: ________________________ [2]
(b) Calculate the average rate at which the copper plate absorbs energy from the Sun.
Working: ______________________________________________________________________
Answer: ________________________ [2]
(c) Explain whether the actual rate of energy absorption from the Sun is higher or lower than your answer in (b).
________________________________________________________________________________ [1]
20. A cold drink at 5 °C is placed outside on a hot day when the air temperature is 30 °C. The same cold drink is also placed outside at night when the air temperature is 10 °C.
(a) Calculate the temperature difference between the drink and the surroundings during the day and during the night.
Day: __________________________________________________________________________ [1]
Night: ________________________________________________________________________ [1]
(b) Explain why the drink warms up more quickly during the day than at night, with reference to the rate of heat transfer.
________________________________________________________________________________ [2]
End of Quiz
Answers
Secondary 4 Pure Physics Quiz - Thermal Physics
Answer Key
1. C
Marking note: Conduction is the transfer of thermal energy through a material without bulk movement of the material itself. [1]
2. B
Marking note: In metals, free electrons gain kinetic energy at the heated end and transfer it through collisions along the rod. [1]
3. B
Working:
Q = mcΔT
m = 200 g = 0.2 kg; c = 900 J/(kg·°C); ΔT = 75 − 25 = 50 °C
Q = 0.2 × 900 × 50 = 9 000 J
Answer: 9 000 J [1]
Common mistake: Forgetting to convert grams to kilograms.
4. C
Marking note: Black, matt surfaces are the best absorbers (and emitters) of infrared radiation. [1]
5. B
Marking note: The rate of cooling is proportional to the temperature difference between the object and surroundings (Newton's law of cooling), so the curve starts steep and flattens. [1]
6.
(a) Specific heat capacity is the amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K). [1]
(b) Thermal equilibrium is the state at which two objects in thermal contact reach the same temperature and there is no net transfer of thermal energy between them. [1]
7.
- Boiling occurs at a fixed temperature (boiling point); evaporation occurs at any temperature. [1]
- Boiling occurs throughout the liquid; evaporation occurs only at the surface. [1]
Acceptable alternatives: Boiling requires a continuous supply of energy; evaporation can cause cooling of the remaining liquid.
8. When the temperature of a gas is raised, the gas molecules gain kinetic energy and move faster. [1] They collide with the walls of the container more frequently and with greater force. [1] Since pressure is force per unit area, the pressure increases. [1]
Award 2 marks for a clear explanation linking molecular speed → collision frequency/force → pressure.
9.
(a) m = 500 g = 0.5 kg; c = 4 200 J/(kg·°C); ΔT = 80 − 20 = 60 °C
Q = mcΔT = 0.5 × 4 200 × 60 = 126 000 J
Answer: 126 000 J (or 1.26 × 10⁵ J) [2]
Award 1 mark for correct formula and substitution; 1 mark for correct answer with unit.
(b) t = 10 min = 600 s
P = Q / t = 126 000 / 600 = 210 W
Answer: 210 W [2]
Award 1 mark for correct formula; 1 mark for correct answer with unit.
10. Copper is a good thermal conductor (high thermal conductivity) because it has free electrons that can transfer kinetic energy rapidly through the material. [1] Glass is a poor thermal conductor (thermal insulator) because it lacks free electrons and transfers thermal energy much more slowly through molecular vibrations. [1]
Award full marks if the student correctly contrasts the two materials in terms of thermal conductivity and the mechanism.
11.
(a) Any one: cooking pan base, heat sink in electronics, radiator, metal spoon. [1]
(b) Any one: handle of cooking pot, fibreglass insulation in walls, polystyrene cup, woollen clothing. [1]
12.
(a) m_iron = 0.8 kg; c_iron = 450 J/(kg·°C); ΔT = 150 − 32 = 118 °C
Q_lost = 0.8 × 450 × 118 = 42 480 J
Answer: 42 480 J (or 42.5 kJ) [2]
Award 1 mark for correct substitution; 1 mark for correct answer.
(b) By conservation of energy (assuming no heat loss to surroundings), thermal energy gained by water = thermal energy lost by iron = 42 480 J.
Answer: 42 480 J [1]
(c) The thermal energy gained by the water should equal the thermal energy lost by the iron. Any small discrepancy is due to heat lost to the container or the surroundings. [1]
Accept any reasonable explanation involving heat loss to the environment.
13. Sunlight (shortwave radiation) passes through the glass windows and is absorbed by the interior surfaces (seats, dashboard), which warm up. [1] These surfaces then emit infrared radiation, which cannot easily pass back through the glass, trapping thermal energy inside (greenhouse effect). [1] The enclosed air inside the car is heated by conduction and convection from the warm interior surfaces. [1] Since the car is enclosed, there is little wind to carry the hot air away, so the temperature builds up. [1]
Award 1 mark each for up to 3 valid points covering at least two heat transfer mechanisms.
14.
(a) The thermal energy supplied is used to break the intermolecular bonds in the ice to change it from solid to liquid (latent heat of fusion), not to raise the temperature. [1]
(b) The internal energy of the water increases because the kinetic energy of the molecules increases as temperature rises. [1]
15.
(a) The black ceramic teapot will cool faster. [1]
(b) Black, matt surfaces are better emitters of infrared radiation than shiny surfaces. [1] The black ceramic teapot radiates thermal energy away more effectively, so it cools faster. The shiny metal teapot reflects infrared radiation and emits less, so it retains heat longer. [1]
Award the explanation mark even if part (a) is wrong, provided the explanation is consistent.
16.
(a) Beaker A (wrapped in aluminium foil) will cool more slowly. [1] The aluminium foil reduces heat loss by radiation (shiny surface is a poor emitter and good reflector of infrared radiation) and also reduces heat loss by convection by acting as a barrier to air movement. [1]
(b) Any one: initial temperature of water, volume/mass of water, room temperature, surface area of beaker. [1]
(c) Both curves should show exponential decay (steep at first, gradually flattening). [1] Curve A should be less steep (cools more slowly) and always above curve B. Both curves should level off towards room temperature. [1]
Deduct 1 mark if curves are straight lines or if they cross.
17.
(a) Q = mcΔT = 0.5 × 2 100 × (100 − 20) = 0.5 × 2 100 × 80 = 84 000 J
Answer: 84 000 J [2]
(b) Q = mcΔT → c = Q / (mΔT) = 168 000 / (0.5 × 80) = 168 000 / 40 = 4 200 J/(kg·°C)
Answer: Water [2]
This confirms the substance is water.
(c) The specific heat capacity of the unknown liquid (2 100 J/(kg·°C)) is half that of water (4 200 J/(kg·°C)). [1]
Accept any valid comparison referencing the specific heat capacity values.
18.
(a) The vacuum between the walls prevents heat transfer by conduction and convection because there are no particles to carry the thermal energy. [1]
(b) The silvered (shiny) surfaces on both sides of the vacuum reduce heat transfer by radiation because shiny surfaces are poor emitters and good reflectors of infrared radiation. [1]
(c) The plastic stopper at the top reduces heat loss by conduction (plastic is a poor conductor) and also reduces heat loss by convection and evaporation from the opening. [1]
Accept any valid design feature with correct explanation.
19.
(a) ΔT = 85 − 25 = 60 °C
Q = mcΔT = 2.0 × 385 × 60 = 46 200 J
Answer: 46 200 J [2]
(b) Rate of heat absorption = Q / t = 46 200 / (5 × 60) = 46 200 / 300 = 154 W
Answer: 154 W [2]
Award 1 mark for correct time conversion; 1 mark for correct final answer.
(c) The actual rate of heat absorption from the Sun would be higher because some energy is lost to the surroundings by conduction, convection, and radiation. [1]
20.
(a) Day: Temperature difference = 30 − 5 = 25 °C [1]
Night: Temperature difference = 10 − 5 = 5 °C [1]
(b) During the day, the temperature difference between the surroundings (30 °C) and the cold drink (5 °C) is large, so heat flows rapidly into the drink by conduction and convection, warming it quickly. [1] At night, the temperature difference is small (only 5 °C), so heat flows into the drink much more slowly, and the drink stays cold for longer. [1]
Accept any answer that correctly links temperature difference to rate of heat transfer.
End of Answer Key