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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: 45 minutes Total Marks: 40
Instructions:
- This quiz contains 20 questions on Thermal Physics.
- Answer ALL questions in the spaces provided.
- Show all working for calculation questions.
- Use g = 10 m/s² where needed.
- Specific heat capacity of water = 4200 J/(kg·K) unless stated otherwise.
Section A: Kinetic Particle Model of Matter (Questions 1–5)
10 marks
1. Smoke particles suspended in air are viewed under a microscope. They are observed to move randomly and jerkily.
(a) Name this phenomenon. [1 mark]
(b) Explain why this observation provides evidence that air molecules are in constant motion. [2 marks]
2. A sealed metal can contains a fixed mass of gas at room temperature. The can is placed in a freezer and its temperature decreases.
(a) Explain, using the kinetic particle model, why the pressure exerted by the gas on the walls of the can decreases. [2 marks]
(b) State what happens to the average kinetic energy of the gas particles. [1 mark]
3. The table below compares some properties of solids, liquids, and gases.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | (i) | (ii) |
| Compressibility | (iii) | Very low | High |
| Particle arrangement | (iv) | Close but disordered | Far apart, random |
Complete the table by filling in (i) to (iv). [4 marks]
(i) _____________________________________________________________________________
(ii) ____________________________________________________________________________
(iii) ___________________________________________________________________________
(iv) ___________________________________________________________________________
Section B: Thermal Processes (Questions 6–10)
10 marks
6. A student investigates heat transfer by placing one end of a copper rod in hot water. The other end of the rod becomes warm after some time.
(a) Name the process by which thermal energy travels along the copper rod. [1 mark]
(b) Explain how this process occurs in metals, referring to both particle vibration and free electrons. [2 marks]
7. A room heater is placed on the floor of a cold room. After some time, the entire room becomes warm.
(a) Name the main process by which thermal energy is transferred throughout the room. [1 mark]
(b) Explain how this process occurs and why the heater is more effective when placed near the floor. [2 marks]
8. A student places her hand near the side of a hot iron. She feels warmth even though her hand is not touching the iron.
(a) Name the process by which thermal energy reaches her hand. [1 mark]
(b) State two factors that affect the rate of energy transfer by this process from the iron. [2 marks]
9. A vacuum flask is designed to keep hot liquids hot and cold liquids cold. It has a double-walled glass container with a vacuum between the walls, and both interior surfaces are silvered.
Explain how each of the following features reduces thermal energy transfer:
(a) The vacuum between the walls. [1 mark]
(b) The silvered surfaces. [1 mark]
10. A student sets up an experiment with a beaker of water and a few crystals of potassium permanganate at the bottom. She heats the beaker gently at one side.
(a) Describe what she observes in the water. [1 mark]
(b) Explain the observation using the concept of density changes. [2 marks]
Section C: Thermal Properties of Matter (Questions 11–15)
10 marks
11. Define the term specific heat capacity of a substance. [2 marks]
12. An electric kettle contains 1.5 kg of water at 25 °C. The kettle has a power rating of 2000 W and is switched on for 4.0 minutes. Assume no energy is lost to the surroundings.
(a) Calculate the thermal energy supplied by the kettle. [2 marks]
(b) Calculate the final temperature of the water. [2 marks] (Specific heat capacity of water = 4200 J/(kg·K))
13. A student heats a solid substance at a constant rate and records its temperature over time. The graph below shows the temperature-time graph obtained.
Temperature / °C
|
80 | D---------E
| /
50 | B-------C
| /
20 | A----
|
+--------------------------------> Time / min
(a) State what is happening to the substance between points B and C. [1 mark]
(b) Explain why the temperature remains constant between B and C even though heating continues. [2 marks]
(c) State the melting point of the substance. [1 mark]
14. Define the term specific latent heat of vaporisation. [2 marks]
15. A 0.80 kg block of ice at 0 °C is placed in a container. A heater supplies energy at a rate of 120 W. The ice melts completely in 35 minutes.
Calculate the specific latent heat of fusion of ice. [3 marks]
Section D: Integrated Thermal Physics (Questions 16–20)
10 marks
16. A student pours 200 g of hot water at 80 °C into a 100 g aluminium cup at 20 °C. The specific heat capacity of aluminium is 900 J/(kg·K).
Calculate the final temperature of the water and the cup, assuming no energy is lost to the surroundings. [3 marks]
17. Explain, using the kinetic particle model, why:
(a) A liquid evaporates faster at a higher temperature. [2 marks]
(b) Evaporation causes cooling of the remaining liquid. [2 marks]
18. A student investigates the cooling of hot water in two identical beakers. Beaker A is painted matt black, and Beaker B is painted shiny white. Both contain the same mass of water at the same initial temperature.
(a) State which beaker cools faster. [1 mark]
(b) Explain your answer. [2 marks]
19. A solar panel absorbs radiation from the Sun and uses it to heat water flowing through pipes.
(a) State the type of electromagnetic radiation primarily responsible for this heating. [1 mark]
(b) Explain why the pipes in the solar panel are often painted black. [2 marks]
20. A 500 W immersion heater is used to heat 2.0 kg of a liquid. The temperature of the liquid rises from 20 °C to 45 °C in 10 minutes. Assume no energy is lost.
Calculate the specific heat capacity of the liquid. [3 marks]
END OF QUIZ
Answers
Secondary 4 Pure Physics Quiz - Thermal Physics — Answer Key
Total Marks: 40
Section A: Kinetic Particle Model of Matter (Questions 1–5)
1. Smoke particles in air under microscope.
(a) Brownian motion [1 mark]
(b) The smoke particles are visible and are much larger than air molecules. [1] The random, jerky motion of the smoke particles is caused by uneven collisions with fast-moving air molecules from all directions. [1] This shows that air molecules are in constant, random motion. [Total: 2 marks]
2. Gas in sealed can placed in freezer.
(a) When the temperature decreases, the average kinetic energy of the gas particles decreases, so they move more slowly. [1] The particles collide with the walls less frequently and with less force. Since pressure is caused by particle collisions with the walls, the pressure decreases. [1] [Total: 2 marks]
(b) The average kinetic energy of the gas particles decreases. [1 mark]
3. Table completion.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | (i) Not fixed / takes shape of container | (ii) Not fixed / fills container |
| Compressibility | (iii) Very low / negligible | Very low | High |
| Particle arrangement | (iv) Closely packed, regular / ordered | Close but disordered | Far apart, random |
Marking:
- (i) Not fixed / takes shape of lower part of container [1 mark]
- (ii) Not fixed / fills entire container [1 mark]
- (iii) Very low / negligible / almost incompressible [1 mark]
- (iv) Closely packed in a regular/ordered pattern/lattice [1 mark]
[Total: 4 marks]
Section B: Thermal Processes (Questions 6–10)
6. Copper rod in hot water.
(a) Conduction [1 mark]
(b) Particles at the hot end of the rod gain kinetic energy and vibrate more vigorously. [1] These vibrations are passed to neighbouring particles through collisions, transferring energy along the rod. In metals, free electrons also move and collide with atoms, transferring energy more rapidly. [1] [Total: 2 marks]
7. Room heater on floor.
(a) Convection [1 mark]
(b) Air near the heater is warmed, expands, and becomes less dense. [1] The less dense warm air rises, while cooler, denser air sinks to take its place, setting up a convection current. Placing the heater near the floor allows the warm air to rise and circulate throughout the entire room more effectively. [1] [Total: 2 marks]
8. Hand near hot iron.
(a) Radiation (accept: infrared radiation / thermal radiation) [1 mark]
(b) Any two from:
- Temperature of the iron (higher temperature → greater rate)
- Surface area of the iron (larger area → greater rate)
- Colour/texture of the surface (darker/matt surfaces emit more radiation) [1 mark each, max 2 marks]
9. Vacuum flask features.
(a) The vacuum contains no particles, so conduction and convection cannot occur across it (both require a medium). [1 mark]
(b) The silvered surfaces are poor emitters and poor absorbers of radiation, so they reflect thermal radiation back, reducing energy transfer by radiation. [1 mark]
10. Potassium permanganate in heated water.
(a) A purple streak rises from the heated side, moves across the top, and sinks down the cooler side, forming a circulating pattern. [1 mark]
(b) Water near the heat source expands and becomes less dense. [1] This less dense water rises. Cooler, denser water sinks to replace it, setting up a convection current that carries the purple colour around. [1] [Total: 2 marks]
Section C: Thermal Properties of Matter (Questions 11–15)
11. Specific heat capacity is the amount of thermal energy required to raise the temperature of 1 kg of the substance by 1 K (or 1 °C). [2 marks — 1 for "per unit mass", 1 for "per unit temperature change"]
12. Electric kettle calculation.
(a) Energy supplied = Power × time = 2000 W × (4.0 × 60) s = 2000 × 240 = 480,000 J (or 480 kJ) [2 marks — 1 for correct formula, 1 for correct answer with units]
(b) Q = mcΔθ 480,000 = 1.5 × 4200 × (θ_final − 25) 480,000 = 6300 × (θ_final − 25) θ_final − 25 = 480,000 ÷ 6300 = 76.2 θ_final = 76.2 + 25 = 101.2 °C
However, water boils at 100 °C, so the final temperature is 100 °C (the water would boil; excess energy goes into vaporisation). [2 marks — 1 for correct method, 1 for recognising boiling point limit and correct final answer]
13. Temperature-time graph interpretation.
(a) The substance is melting (changing from solid to liquid). [1 mark]
(b) During melting, the thermal energy supplied is used to break the bonds between particles (increase potential energy) rather than increase kinetic energy. [1] Since temperature is a measure of average kinetic energy, the temperature remains constant until all the solid has melted. [1] [Total: 2 marks]
(c) 50 °C [1 mark]
14. Specific latent heat of vaporisation is the amount of thermal energy required to change 1 kg of a substance from liquid to gas (or gas to liquid) without a change in temperature. [2 marks — 1 for "per unit mass", 1 for "change of state without temperature change"]
15. Ice melting calculation.
Energy supplied = Power × time = 120 W × (35 × 60) s = 120 × 2100 = 252,000 J [1 mark]
Q = mL 252,000 = 0.80 × L L = 252,000 ÷ 0.80 = 315,000 J/kg (or 3.15 × 10⁵ J/kg) [2 marks — 1 for correct substitution, 1 for correct answer with units]
[Total: 3 marks]
Section D: Integrated Thermal Physics (Questions 16–20)
16. Hot water and aluminium cup.
Energy lost by water = Energy gained by cup m_w × c_w × (80 − θ) = m_c × c_c × (θ − 20) [1 mark]
0.200 × 4200 × (80 − θ) = 0.100 × 900 × (θ − 20) 840 × (80 − θ) = 90 × (θ − 20) 67,200 − 840θ = 90θ − 1800 67,200 + 1800 = 90θ + 840θ 69,000 = 930θ [1 mark] θ = 69,000 ÷ 930 = 74.2 °C [1 mark]
[Total: 3 marks]
17. Evaporation and kinetic particle model.
(a) At a higher temperature, more particles near the liquid surface have sufficient kinetic energy to overcome the attractive forces of neighbouring particles and escape from the liquid. [1] The higher the temperature, the greater the proportion of particles with enough energy to escape, so evaporation occurs faster. [1] [Total: 2 marks]
(b) When the most energetic particles escape from the liquid surface, the average kinetic energy of the remaining particles decreases. [1] Since temperature is a measure of average kinetic energy, the temperature of the remaining liquid falls — this is evaporative cooling. [1] [Total: 2 marks]
18. Cooling in black and white beakers.
(a) Beaker A (matt black) cools faster. [1 mark]
(b) Matt black surfaces are better emitters of thermal radiation than shiny white surfaces. [1] Therefore, Beaker A radiates thermal energy at a higher rate, causing it to cool faster. [1] [Total: 2 marks]
19. Solar panel.
(a) Infrared radiation (accept: thermal radiation / electromagnetic radiation from the Sun) [1 mark]
(b) Black surfaces are good absorbers of radiation. [1] Painting the pipes black maximises the absorption of thermal radiation from the Sun, increasing the efficiency of heating the water. [1] [Total: 2 marks]
20. Specific heat capacity of liquid.
Energy supplied = Power × time = 500 W × (10 × 60) s = 500 × 600 = 300,000 J [1 mark]
Q = mcΔθ 300,000 = 2.0 × c × (45 − 20) 300,000 = 2.0 × c × 25 300,000 = 50c [1 mark] c = 300,000 ÷ 50 = 6000 J/(kg·K) [1 mark]
[Total: 3 marks]
END OF ANSWER KEY