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Secondary 4 Pure Physics Thermal Physics Quiz

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Secondary 4 Pure Physics Quiz - Thermal Physics

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 40

Duration: 45 minutes
Total Marks: 40
Instructions:

Answer all questions.
Write your answers in the spaces provided.
Show all working clearly.
Take the acceleration of free fall, $g = 10 \text{ m/s}^2$ (where applicable).
Specific heat capacity of water $c_w = 4200 \text{ J/(kg}^\circ\text{C)}$ .
Specific latent heat of fusion of ice $L_f = 334,000 \text{ J/kg}$ .
Specific latent heat of vaporisation of water $L_v = 2,260,000 \text{ J/kg}$ .

Section A: Kinetic Particle Model & Thermal Processes (Questions 1–5)

1. Which statement correctly describes the arrangement and motion of particles in a liquid? [1]
A. Particles are closely packed in a regular pattern and vibrate about fixed positions.
B. Particles are far apart and move randomly at high speeds.
C. Particles are closely packed but can slide past one another.
D. Particles are arranged in layers and do not move.

Answer: __________________________

2. A student observes smoke particles under a microscope. The particles are seen moving in a random, zig-zag path.
(a) Name this phenomenon. [1]
Answer: __________________________

(b) Explain what this observation suggests about the air molecules surrounding the smoke particles. [2]
Answer:

3. Figure 1 shows a metal rod being heated at one end. The temperature at the other end rises after some time.
(a) Name the primary method of thermal energy transfer through the metal rod. [1]
Answer: __________________________

(b) Explain, in terms of particles and electrons, how thermal energy is transferred in metals. [2]
Answer:

4. A room is heated by an electric heater placed near the floor.
(a) Name the process by which thermal energy is transferred through the air in the room. [1]
Answer: __________________________

(b) Explain why the heater is placed near the floor rather than the ceiling. [2]
Answer:

5. Two identical cans, one painted black and the other painted white, are filled with hot water at the same initial temperature. They are left to cool in the same room.
(a) Which can will cool down faster? [1]
Answer: __________________________

(b) Explain your answer. [1]
Answer:

Section B: Thermal Properties of Matter (Questions 6–12)

6. Define specific heat capacity. [2]
Answer:

7. Calculate the thermal energy required to raise the temperature of 0.5 kg of water from $20^\circ\text{C}$ to $80^\circ\text{C}$ . [2]
Answer:
 Energy = __________________________ J

8. A 2 kg block of aluminium absorbs 18,000 J of thermal energy. Its temperature rises by $10^\circ\text{C}$ . Calculate the specific heat capacity of aluminium. [2]
Answer:
 Specific heat capacity = __________________________ J/(kg $^\circ$ C)

9. Figure 2 shows a cooling curve for a pure substance.
(Imagine a graph: Temp vs Time. Slope down, then flat horizontal line, then slope down again.)
(a) What is happening to the substance during the horizontal section of the graph? [1]
Answer: __________________________

(b) Explain, in terms of energy and particle arrangement, why the temperature remains constant during this phase, even though energy is being lost. [2]
Answer:

10. Define specific latent heat of vaporisation. [2]
Answer:

11. Calculate the energy required to convert 0.2 kg of boiling water at $100^\circ\text{C}$ completely into steam at $100^\circ\text{C}$ . [2]
Answer:
 Energy = __________________________ J

12. Explain the difference between boiling and evaporation. Give two differences. [2]
Answer:

Section C: Applications & Calculations (Questions 13–20)

13. A student wants to measure the specific heat capacity of a metal block.
(a) State two measurements the student must take. [2]
Answer:

(b) Suggest one way to reduce heat loss to the surroundings during the experiment. [1]
Answer:

14. Why is water often used as a coolant in car engines? Refer to its specific heat capacity in your answer. [2]
Answer:

15. An electric kettle has a power rating of 2000 W. It contains 1.0 kg of water at $25^\circ\text{C}$ .
(a) Calculate the energy required to heat the water to its boiling point ( $100^\circ\text{C}$ ). [2]
Answer:
 Energy = __________________________ J

(b) Calculate the minimum time required to heat the water to boiling, assuming no energy is lost. [2]
Answer:
 Time = __________________________ s

16. Using the kettle in Q15, calculate the additional energy required to convert all the boiling water into steam. [2]
Answer:
 Energy = __________________________ J

17. Explain why a person feels colder when wind blows on their wet skin compared to still air. [2]
Answer:

18. A double-glazed window consists of two panes of glass with a layer of air trapped between them.
(a) Explain how the trapped air reduces thermal energy loss. [2]
Answer:

(b) Why is a vacuum better than air for reducing thermal energy transfer? [1]
Answer:

19. In a vacuum flask, the inner walls are silvered.
(a) Which method of heat transfer does the silvered surface primarily reduce? [1]
Answer: __________________________

(b) Explain how the silvered surface achieves this. [1]
Answer:

20. 0.1 kg of ice at $0^\circ\text{C}$ is added to 0.5 kg of water at $20^\circ\text{C}$ .
(a) Calculate the energy required to melt the ice completely at $0^\circ\text{C}$ . [2]
Answer:
 Energy = __________________________ J

(b) Without performing further calculations, state whether the final temperature of the mixture will be above, below, or exactly $0^\circ\text{C}$ , and give a brief reason. [2]
Answer:

End of Quiz

Answers

Secondary 4 Pure Physics Quiz - Thermal Physics (Answer Key)

1. C
[1 mark]

2.
(a) Brownian motion [1]
(b) Air molecules are in constant random motion [1]. They collide with the smoke particles from different directions, causing the random zig-zag movement [1].
[Total: 3 marks]

3.
(a) Conduction [1]
(b) Free electrons gain kinetic energy and move rapidly through the metal lattice, colliding with atoms/ions and transferring energy [1]. The atoms/ions also vibrate more vigorously and pass this vibration to neighbouring atoms [1].
[Total: 3 marks]

4.
(a) Convection [1]
(b) Air near the heater warms up, expands, and becomes less dense [1]. The warm air rises, and cooler, denser air sinks to replace it, creating a convection current that circulates heat through the room [1].
[Total: 3 marks]

5.
(a) The black can [1]
(b) Black surfaces are better emitters of infrared radiation than white/shiny surfaces [1].
[Total: 2 marks]

6. The amount of thermal energy required to raise the temperature of 1 kg of a substance by $1^\circ\text{C}$ (or 1 K) [2].
[2 marks]

7.
$Q = mc\Delta T$
$Q = 0.5 \times 4200 \times (80 - 20)$
$Q = 0.5 \times 4200 \times 60$
$Q = 126,000 \text{ J}$
[2 marks: 1 for formula/substitution, 1 for answer]

8.
$Q = mc\Delta T \Rightarrow c = Q / (m\Delta T)$
$c = 18,000 / (2 \times 10)$
$c = 18,000 / 20$
$c = 900 \text{ J/(kg}^\circ\text{C)}$
[2 marks: 1 for rearrangement/substitution, 1 for answer]

9.
(a) Freezing (or solidification) [1]
(b) Energy is being released as the particles change from a liquid arrangement to a solid arrangement (potential energy decreases) [1]. The average kinetic energy of the particles remains constant, so the temperature does not change [1].
[Total: 3 marks]

10. The amount of thermal energy required to convert 1 kg of a substance from liquid to gas at its boiling point without a change in temperature [2].
[2 marks]

11.
$Q = mL_v$
$Q = 0.2 \times 2,260,000$
$Q = 452,000 \text{ J}$
[2 marks: 1 for formula/substitution, 1 for answer]

12.

Boiling occurs at a fixed temperature (boiling point); evaporation occurs at any temperature [1].
Boiling occurs throughout the liquid (bubbles); evaporation occurs only at the surface [1].
[2 marks]

13.
(a) Any two: Mass of block, Initial temperature, Final temperature, Time heater is on, Current/Voltage (if electrical method) [2].
(b) Insulate the block / Use a lid / Polish the surface / Perform experiment quickly [1].
[Total: 3 marks]

14. Water has a high specific heat capacity [1]. This means it can absorb a large amount of thermal energy from the engine without a large rise in temperature, keeping the engine cool [1].
[2 marks]

15.
(a) $\Delta T = 100 - 25 = 75^\circ\text{C}$
$Q = 1.0 \times 4200 \times 75$
$Q = 315,000 \text{ J}$
[2 marks]
(b) $P = E/t \Rightarrow t = E/P$
$t = 315,000 / 2000$
$t = 157.5 \text{ s}$
[2 marks]

16.
$Q = mL_v$
$Q = 1.0 \times 2,260,000$
$Q = 2,260,000 \text{ J}$
[2 marks]

17. The wind increases the rate of evaporation of water from the skin [1]. Evaporation requires latent heat, which is taken from the body/skin, causing a cooling effect [1].
[2 marks]

18.
(a) Air is a poor conductor of heat [1]. Trapping it prevents convection currents from forming between the panes [1].
(b) A vacuum contains no particles, so heat cannot be transferred by conduction or convection [1].
[Total: 3 marks]

19.
(a) Radiation [1]
(b) Silvered surfaces are poor emitters and good reflectors of infrared radiation, reflecting heat back into the flask [1].
[Total: 2 marks]

20.
(a) $Q = mL_f$
$Q = 0.1 \times 334,000$
$Q = 33,400 \text{ J}$
[2 marks]
(b) Above $0^\circ\text{C}$ [1]. The energy released by the water cooling from $20^\circ\text{C}$ to $0^\circ\text{C}$ ( $0.5 \times 4200 \times 20 = 42,000 \text{ J}$ ) is greater than the energy required to melt the ice ( $33,400 \text{ J}$ ), so there is excess energy to raise the temperature of the mixture [1].
[Total: 4 marks]