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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
Instructions:
- Answer ALL questions.
- Show your working clearly for calculation questions. Include units where appropriate.
- Write your answers in the spaces provided.
- The number of marks for each question is shown in brackets [ ].
Section A: Multiple Choice Questions (10 marks)
Questions 1–10: Choose the most correct answer. Each question carries 1 mark.
1. Which of the following best describes the process of thermal conduction?
(A) Transfer of thermal energy through the bulk movement of a fluid
(B) Transfer of thermal energy through electromagnetic waves
(C) Transfer of thermal energy through molecular vibrations and collisions without bulk movement of the material
(D) Transfer of thermal energy only in gases and liquids
Answer: _______________
2. A metal rod is heated at one end. After some time, the other end becomes warm. Which property of the metal determines how quickly thermal energy is conducted along the rod?
(A) Specific heat capacity
(B) Thermal conductivity
(C) Density
(D) Specific latent heat
Answer: _______________
3. The specific heat capacity of a substance is defined as the amount of thermal energy required to:
(A) raise the temperature of the substance by 1 °C
(B) raise the temperature of 1 kg of the substance by 1 °C
(C) change the state of 1 kg of the substance
(D) raise the temperature of 1 kg of the substance by 1 K at constant pressure
Answer: _______________
4. Two beakers of water at 80 °C and 30 °C are mixed. Assuming no heat loss, which statement is correct?
(A) Heat flows from the 30 °C water to the 80 °C water
(B) The final temperature is exactly 55 °C regardless of the masses
(C) Heat flows from the 80 °C water to the 30 °C water until thermal equilibrium is reached
(D) The final temperature must be above 80 °C
Answer: _______________
5. During the boiling of water at 100 °C, which of the following is true?
(A) The temperature of the water increases steadily
(B) The temperature of the water decreases
(C) The temperature remains constant while thermal energy is being supplied
(D) No thermal energy is absorbed
Answer: _______________
6. Which surface is the best emitter of thermal radiation?
(A) Shiny silver surface
(B) White polished surface
(C) Matt black surface
(D) Transparent glass surface
Answer: _______________
7. A 2 kg block of aluminium (specific heat capacity = 900 J kg⁻¹ °C⁻¹) is heated from 25 °C to 75 °C. How much thermal energy is absorbed?
(A) 45 000 J
(B) 90 000 J
(C) 180 000 J
(D) 22 500 J
Answer: _______________
8. Convection currents in a fluid occur because:
(A) the fluid molecules radiate energy as they move
(B) the heated part of the fluid becomes less dense and rises, while the cooler, denser part sinks
(C) thermal energy is transferred through direct contact between molecules
(D) electromagnetic waves carry energy through the fluid
Answer: _______________
9. The specific latent heat of fusion of ice is 3.4 × 10⁵ J kg⁻¹. How much energy is needed to melt 0.5 kg of ice at 0 °C without changing its temperature?
(A) 1.7 × 10⁵ J
(B) 3.4 × 10⁵ J
(C) 6.8 × 10⁵ J
(D) 1.7 × 10⁴ J
Answer: _______________
10. A thermometer is placed in a cup of hot coffee. The reading rises and then stabilises. The thermometer reading stabilises when:
(A) the thermometer stops absorbing energy
(B) the coffee has cooled to 0 °C
(C) the thermometer and the coffee are at the same temperature
(D) all the thermal energy has been lost to the surroundings
Answer: _______________
Section B: Structured Questions (20 marks)
Questions 11–16: Answer in the spaces provided. Show all working.
11. Define the following terms: [4]
(a) Specific heat capacity:
(b) Specific latent heat of vaporisation:
12. A 0.8 kg copper block is heated using an electric heater. The temperature of the block rises from 22 °C to 62 °C in 4 minutes. The specific heat capacity of copper is 390 J kg⁻¹ °C⁻¹. [4]
(a) Calculate the thermal energy absorbed by the copper block.
Working:
Answer: _______________ J
(b) Calculate the power of the heater, assuming no energy is lost to the surroundings.
Working:
Answer: _______________ W
13. Fig. 13 (not shown) shows a hot water tank used in a household. The tank is insulated with a layer of foam. [3]
(a) Explain how the foam insulation reduces thermal energy loss from the tank. Refer to conduction, convection, and radiation in your answer.
(b) State one other method, besides insulation, to reduce thermal energy loss from the tank.
14. 0.2 kg of water at 100 °C is converted into steam at 100 °C. The specific latent heat of vaporisation of water is 2.3 × 10⁶ J kg⁻¹. [2]
(a) Calculate the thermal energy required to convert all the water into steam.
Working:
Answer: _______________ J
(b) State one assumption made in your calculation.
15. Explain, in terms of molecular behaviour, why a metal feels colder to the touch than a wooden block at the same temperature. [3]
16. A student carries out an experiment to compare the rates of cooling of two liquids, X and Y. Both liquids have the same mass and the same starting temperature of 90 °C. The temperature of each liquid is recorded every minute. The results are shown in the table below. [4]
| Time / min | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| Temp of X / °C | 90 | 82 | 75 | 69 | 64 | 60 | 57 |
| Temp of Y / °C | 90 | 78 | 68 | 60 | 54 | 50 | 47 |
(a) Which liquid cools faster? Explain your answer.
(b) Suggest a reason for the difference in the rate of cooling between the two liquids.
(c) State one variable that must be kept constant in this experiment to ensure a fair test.
Section C: Free Response Question (10 marks)
Questions 17–20: Answer in the spaces provided. Show all working.
17. A 1.5 kg block of ice at −10 °C is heated until it becomes water at 30 °C. [6]
Given:
Specific heat capacity of ice = 2100 J kg⁻¹ °C⁻¹
Specific latent heat of fusion of ice = 3.4 × 10⁵ J kg⁻¹
Specific heat capacity of water = 4200 J kg⁻¹ °C⁻¹
(a) Calculate the thermal energy required to raise the temperature of the ice from −10 °C to 0 °C.
Working:
Answer: _______________ J
(b) Calculate the thermal energy required to melt all the ice at 0 °C.
Working:
Answer: _______________ J
(c) Calculate the thermal energy required to raise the temperature of the water from 0 °C to 30 °C.
Working:
Answer: _______________ J
(d) Calculate the total thermal energy required for the entire process.
Working:
Answer: _______________ J
18. A solar water heater uses radiation from the Sun to heat water flowing through blackened copper pipes inside a glass-covered panel. [4]
(a) Explain why the copper pipes are painted black.
(b) Explain the purpose of the glass cover over the panel.
(c) The water flows slowly through the pipes. Explain why a slow flow rate results in hotter water at the outlet.
19. A cup of tea at 85 °C is left on a table in a room at 25 °C. [3]
(a) Sketch a graph of temperature (y-axis) against time (x-axis) for the cooling of the tea. Label the starting temperature and the room temperature on your graph.
(Sketch in the space below)
(b) Explain the shape of your graph in terms of the rate of thermal energy loss.
20. A 0.5 kg sample of an unknown metal is heated to 100 °C and then placed into 0.4 kg of water at 20 °C in a copper calorimeter of mass 0.15 kg. The final temperature of the mixture is 28 °C. [4]
Given:
Specific heat capacity of water = 4200 J kg⁻¹ °C⁻¹
Specific heat capacity of copper = 390 J kg⁻¹ °C⁻¹
(a) Calculate the thermal energy gained by the water.
Working:
Answer: _______________ J
(b) Calculate the thermal energy gained by the copper calorimeter.
Working:
Answer: _______________ J
(c) Using the principle of conservation of energy, calculate the specific heat capacity of the unknown metal.
Working:
Answer: _______________ J kg⁻¹ °C⁻¹
End of Quiz
Answers
Secondary 4 Pure Physics Quiz - Thermal Physics
Answer Key
Section A: Multiple Choice Questions
1. (C)
Explanation: Thermal conduction is the transfer of thermal energy through a material without the bulk movement of the material itself. Energy is passed from molecule to molecule through vibrations and collisions. [1]
2. (B)
Explanation: Thermal conductivity is the property that determines how well a material conducts thermal energy. Metals have high thermal conductivity. [1]
3. (B)
Explanation: Specific heat capacity is defined as the amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K). [1]
4. (C)
Explanation: Heat always flows from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached. The final temperature depends on the masses of water in each beaker, so it is not necessarily 55 °C. [1]
5. (C)
Explanation: During a change of state (boiling), the temperature remains constant even though thermal energy is continuously supplied. The energy is used to overcome intermolecular forces, not to increase kinetic energy. [1]
6. (C)
Explanation: A matt black surface is the best absorber and best emitter of thermal radiation. Shiny/white surfaces are poor emitters (good reflectors). [1]
7. (B)
Working: Q = mcΔT = 2 × 900 × (75 − 25) = 2 × 900 × 50 = 90 000 J
Answer: 90 000 J [1]
8. (B)
Explanation: When a fluid is heated, it expands, becomes less dense, and rises. Cooler, denser fluid sinks to replace it, creating a convection current. [1]
9. (A)
Working: Q = mL = 0.5 × 3.4 × 10⁵ = 1.7 × 10⁵ J
Answer: 1.7 × 10⁵ J [1]
10. (C)
Explanation: Thermal equilibrium is reached when the thermometer and the coffee are at the same temperature, so there is no net heat flow between them. [1]
Section B: Structured Questions
11. [4]
(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). [2]
Marking: 1 mark for "1 kg", 1 mark for "by 1 °C / 1 K"
(b) Specific latent heat of vaporisation is the amount of thermal energy required to change 1 kg of a substance from liquid to gas (at its boiling point) without a change in temperature. [2]
Marking: 1 mark for "1 kg", 1 mark for "liquid to gas / change of state at constant temperature"
12. [4]
(a) Q = mcΔT
Q = 0.8 × 390 × (62 − 22)
Q = 0.8 × 390 × 40
Q = 12 480 J [2]
Marking: 1 mark for correct formula and substitution, 1 mark for correct answer with unit
(b) P = E / t
P = 12 480 / (4 × 60)
P = 12 480 / 240
P = 52 W [2]
Marking: 1 mark for correct formula and substitution (including time conversion), 1 mark for correct answer with unit
13. [3]
(a) The foam insulation reduces thermal energy loss by:
- Conduction: The foam is a poor conductor of heat (low thermal conductivity), so it reduces the transfer of thermal energy by conduction through the walls of the tank. [1]
- Convection: The foam traps air pockets. Air is a poor conductor and the trapped air prevents convection currents from forming within the insulation layer. [1]
- Radiation: The foam reduces radiative heat transfer from the surface of the tank (or the inner surface of the foam reflects some radiation back). [1]
Marking: 1 mark per valid point, up to 3 marks
(b) Any one of:
- Use a shiny/reflective outer surface on the tank to reduce radiation loss
- Place the tank in an enclosed/indoor space to reduce exposure to wind/cool air
- Use a lid/cover on the tank to reduce evaporation and convection from the surface
[1]
14. [2]
(a) Q = mL
Q = 0.2 × 2.3 × 10⁶
Q = 4.6 × 10⁵ J [1]
Marking: 1 mark for correct answer with unit
(b) Assumption: No thermal energy is lost to the surroundings / all the energy supplied goes into converting water to steam. [1]
15. [3]
Metal has a much higher thermal conductivity than wood. [1] When you touch the metal, it conducts thermal energy away from your hand much faster than the wood does. [1] This rapid loss of thermal energy from your skin makes the metal feel colder, even though both are at the same temperature. [1]
Marking: 1 mark for mentioning thermal conductivity, 1 mark for faster heat transfer from hand, 1 mark for linking to sensation of coldness
16. [4]
(a) Liquid Y cools faster. [1] Over the same time period (6 min), liquid Y drops from 90 °C to 47 °C (a drop of 43 °C), whereas liquid X only drops from 90 °C to 57 °C (a drop of 33 °C). [1]
Marking: 1 mark for identifying Y, 1 mark for supporting with data
(b) Liquid Y may have a lower specific heat capacity than liquid X, so it loses thermal energy more quickly for the same rate of heat loss. OR Liquid Y may have a greater surface area exposed to the surroundings, increasing the rate of heat loss. OR The beaker for liquid Y may be made of a better conducting material. [1]
Marking: 1 mark for any valid suggestion
(c) Any one of: surface area of the liquid exposed to air / type of beaker used / starting temperature / room temperature / volume (or mass) of liquid [1]
Section C: Free Response Questions
17. [6]
(a) Q₁ = mcΔT (ice)
Q₁ = 1.5 × 2100 × (0 − (−10))
Q₁ = 1.5 × 2100 × 10
Q₁ = 31 500 J [1]
(b) Q₂ = mL
Q₂ = 1.5 × 3.4 × 10⁵
Q₂ = 5.1 × 10⁵ J (or 510 000 J) [1]
(c) Q₃ = mcΔT (water)
Q₃ = 1.5 × 4200 × (30 − 0)
Q₃ = 1.5 × 4200 × 30
Q₃ = 189 000 J [1]
(d) Q_total = Q₁ + Q₂ + Q₃
Q_total = 31 500 + 510 000 + 189 000
Q_total = 730 500 J (or 7.305 × 10⁵ J) [2]
Marking: 1 mark for adding all three values, 1 mark for correct final answer
Note: Accept 7.3 × 10⁵ J if rounded
18. [4]
(a) Black surfaces are good absorbers of thermal radiation. [1] Painting the pipes black maximises the amount of solar radiation absorbed, so more thermal energy is transferred to the water. [1]
Marking: 1 mark for "good absorber", 1 mark for linking to increased energy transfer
(b) The glass cover allows short-wavelength solar radiation to pass through and enter the panel. [1] It also traps the longer-wavelength infrared radiation emitted by the heated pipes (greenhouse effect), reducing thermal energy loss by radiation. It also reduces heat loss by convection by acting as a physical barrier to air currents. [1]
Marking: 1 mark for allowing solar radiation in / greenhouse effect, 1 mark for reducing convection/radiation loss
(c) When water flows slowly, each unit of water spends more time inside the pipes. [1] This allows more thermal energy to be transferred from the hot pipes to the water, resulting in a higher outlet temperature. [1]
Marking: 1 mark for longer time in pipes, 1 mark for more energy transferred leading to higher temperature
19. [3]
(a) Sketch graph:
- Temperature starts at 85 °C at time = 0
- Curve decreases steeply at first, then gradually flattens
- Curve asymptotically approaches 25 °C (room temperature)
- Never goes below 25 °C
[2]
Marking: 1 mark for correct starting point and general shape (exponential decay curve), 1 mark for correct asymptote at 25 °C
(b) The rate of thermal energy loss is greatest when the temperature difference between the tea and the room is largest (at the start). [1] As the tea cools, the temperature difference decreases, so the rate of thermal energy loss decreases. [1] The tea approaches room temperature, so the rate of cooling approaches zero. [1]
Marking: 1 mark for linking rate to temperature difference, 1 mark for rate decreasing over time, 1 mark for approaching zero rate at room temperature
20. [4]
(a) Q_water = m_w × c_w × ΔT
Q_water = 0.4 × 4200 × (28 − 20)
Q_water = 0.4 × 4200 × 8
Q_water = 13 440 J [1]
(b) Q_calorimeter = m_cu × c_cu × ΔT
Q_calorimeter = 0.15 × 390 × (28 − 20)
Q_calorimeter = 0.15 × 390 × 8
Q_calorimeter = 468 J [1]
(c) By conservation of energy:
Thermal energy lost by metal = Thermal energy gained by water + Thermal energy gained by calorimeter
m_metal × c_metal × (100 − 28) = 13 440 + 468
0.5 × c_metal × 72 = 13 908
c_metal = 13 908 / (0.5 × 72)
c_metal = 13 908 / 36
c_metal = 386.3 J kg⁻¹ °C⁻¹ (accept 386 J kg⁻¹ °C⁻¹) [2]
Marking: 1 mark for correct energy conservation equation, 1 mark for correct final answer
Total: 40 marks