Secondary 3 Physics Thermal Physics Quiz

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Secondary 3 Physics Quiz - Thermal Physics

Name: ______________________
Class: ______________________
Date: ______________________
Score: _______ / 40

Duration: 50 minutes
Total Marks: 40
Instructions: Answer all 20 questions. Show your working where calculation is required. Use $g = 10\ \text{m s}^{-2}$ and $c_{\text{water}} = 4200\ \text{J kg}^{-1}\ ^\circ\text{C}^{-1}$ where needed.

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Section A: Multiple Choice and Short Answer (Questions 1–8)

1. Which of the following is the correct SI unit for temperature? [1 mark]
A. °C
B. K
C. J
D. W

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2. State what is meant by the specific heat capacity of a substance. [1 mark]

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3. A metal block of mass $0.20\ \text{kg}$ is heated and its temperature rises by $15\ ^\circ\text{C}$. If $1800\ \text{J}$ of heat is supplied, calculate its specific heat capacity. [2 marks]

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4. Which process transfers heat by the actual movement of fluid particles? [1 mark]
A. Conduction
B. Convection
C. Radiation
D. Insulation

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5. Explain why a shiny surface is a poor radiator of heat. [1 mark]

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6. Define latent heat of vaporisation. [1 mark]

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7. The temperature-time graph below shows ice warming, melting, and then water heating.

Image pending generation: graph for Q7.

State the temperature at which the ice melts. [1 mark]

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8. Calculate the heat required to raise the temperature of $0.50\ \text{kg}$ of water from $20\ ^\circ\text{C}$ to $100\ ^\circ\text{C}$. [2 marks]

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Section B: Structured Questions (Questions 9–15)

9. A copper block of mass $0.40\ \text{kg}$ at $95\ ^\circ\text{C}$ is placed in $0.25\ \text{kg}$ of water at $18\ ^\circ\text{C}$. The final temperature is $33\ ^\circ\text{C}$.
(a) Calculate the heat gained by the water. [2 marks]
(b) Calculate the specific heat capacity of copper. [2 marks]

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10. Describe an experiment using a copper calorimeter to measure the specific heat capacity of a liquid. Include the measurements needed. [3 marks]

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11. $0.10\ \text{kg}$ of ice at $0\ ^\circ\text{C}$ is converted to water at $0\ ^\circ\text{C}$. The latent heat of fusion of ice is $3.34 \times 10^5\ \text{J kg}^{-1}$.
(a) Calculate the heat needed. [2 marks]
(b) State what happens to the energy supplied during melting. [1 mark]

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12. The diagram shows a vacuum flask.

Image pending generation: diagram for Q12.

Explain how the flask reduces heat loss by conduction and radiation. [2 marks]

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13. A heater of power $50\ \text{W}$ is used to heat $0.40\ \text{kg}$ of oil. The temperature rises from $25\ ^\circ\text{C}$ to $45\ ^\circ\text{C}$ in $4$ minutes. Calculate the specific heat capacity of the oil. [3 marks]

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14. State two differences between boiling and evaporation. [2 marks]

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15. A black metal plate and a white metal plate of same size are placed equally near a heater. Explain which plate becomes hotter and why. [2 marks]

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Section C: Applied and Extended Questions (Questions 16–20)

16. A student claims: "When water boils, its temperature keeps rising if heating continues." State whether this is correct and explain. [2 marks]

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17. A household kettle has a power of $2.0\ \text{kW}$. It is used to boil $1.5\ \text{kg}$ of water from $20\ ^\circ\text{C}$ to $100\ ^\circ\text{C}$.
(a) Calculate the heat required. [2 marks]
(b) Calculate the minimum time needed if all energy is transferred to the water. [2 marks]

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18. Describe how you would use a cooling curve to determine the melting point of a wax sample. [3 marks]

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19. The figure shows a convection current in a room with a heater on the floor.

Image pending generation: diagram for Q19.

Explain how convection circulates the air in the room. [3 marks]

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20. A $0.30\ \text{kg}$ aluminium block ($c = 900\ \text{J kg}^{-1}\ ^\circ\text{C}^{-1}$) at $100\ ^\circ\text{C}$ is placed into $0.50\ \text{kg}$ of water at $15\ ^\circ\text{C}$ in a polystyrene cup. Assuming no heat loss, calculate the final temperature. [4 marks]

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Secondary 3 Physics Quiz - Thermal Physics (Answer Key)

Total Marks: 40
Teaching notes included for each question.

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Section A

1. B [1 mark]
Temperature in SI is measured in kelvin (K). °C is common but not SI base; J is energy; W is power.
Teaching note: The SI base unit for temperature is the kelvin. Always link units to quantities.

2. [1 mark]
Specific heat capacity is the amount of heat energy required to raise the temperature of $1\ \text{kg}$ of the substance by $1\ ^\circ\text{C}$ (or $1\ \text{K}$).
Teaching note: Definition must include per unit mass and per degree temperature rise.

3. [2 marks]
Use $Q = mc\Delta T$
$m = 0.20\ \text{kg}$, $\Delta T = 15\ ^\circ\text{C}$, $Q = 1800\ \text{J}$
$c = \frac{Q}{m\Delta T} = \frac{1800}{0.20 \times 15} = \frac{1800}{3} = 600\ \text{J kg}^{-1}\ ^\circ\text{C}^{-1}$
Marking: 1 mark formula/substitution, 1 mark answer with unit.

4. B [1 mark]
Convection is heat transfer by movement of fluid (liquid/gas) particles.

5. [1 mark]
Shiny surfaces reflect infrared radiation and emit less radiation; thus they are poor radiators.
Teaching note: Good reflectors are poor emitters and poor absorbers.

6. [1 mark]
Latent heat of vaporisation is the heat required to change $1\ \text{kg}$ of a liquid at its boiling point into vapour without temperature change.

7. 0°C [1 mark]
From graph, flat region at 0°C is the melting phase.
Visual check: Q7-fig1 shows flat at 0°C from 2–5 min.

8. [2 marks]
$Q = mc\Delta T = 0.50 \times 4200 \times (100 - 20) = 0.50 \times 4200 \times 80 = 168\,000\ \text{J}$
Marking: 1 mark working, 1 mark final answer.

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Section B

9. [4 marks total]
(a) [2] Heat gained by water: $Q_w = m_w c_w \Delta T_w = 0.25 \times 4200 \times (33 - 18) = 0.25 \times 4200 \times 15 = 15\,750\ \text{J}$
(b) [2] Heat lost by copper = heat gained by water = $15\,750\ \text{J}$
$c_{\text{Cu}} = \frac{Q}{m\Delta T} = \frac{15\,750}{0.40 \times (95 - 33)} = \frac{15\,750}{0.40 \times 62} = \frac{15\,750}{24.8} \approx 635\ \text{J kg}^{-1}\ ^\circ\text{C}^{-1}$
Common mistake: using wrong mass or final temp difference.

10. [3 marks]

• Place liquid of known mass in copper calorimeter. [1]
• Record initial temp, heat with known-power heater for set time, record final temp. [1]
• Use $E = Pt = mc\Delta T$ to find $c$; measure mass, temps, time, power. [1]

11. [3 marks]
(a) [2] $Q = mL = 0.10 \times 3.34 \times 10^5 = 3.34 \times 10^4\ \text{J}$
(b) [1] Energy breaks bonds / changes state, temperature unchanged.

12. [2 marks]
Vacuum between walls stops conduction (no particles). [1] Silvered surfaces reflect radiation. [1]
Visual: Q12-fig1 must show vacuum and silvering.

13. [3 marks]
Energy supplied: $E = Pt = 50 \times (4 \times 60) = 50 \times 240 = 12\,000\ \text{J}$
$Q = mc\Delta T \Rightarrow c = \frac{12\,000}{0.40 \times (45 - 25)} = \frac{12\,000}{0.40 \times 20} = \frac{12\,000}{8} = 1500\ \text{J kg}^{-1}\ ^\circ\text{C}^{-1}$
Marking: 1 energy, 1 substitution, 1 answer.

14. [2 marks]

• Boiling occurs at fixed temperature; evaporation at any temperature. [1]
• Boiling throughout liquid; evaporation only at surface. [1]

15. [2 marks]
Black plate becomes hotter. [1] Black surfaces absorb radiation better than white/shiny surfaces. [1]

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Section C

16. [2 marks]
Incorrect. [1] At boiling, temperature stays constant until all water turns to vapour. [1]

17. [4 marks]
(a) [2] $Q = mc\Delta T = 1.5 \times 4200 \times (100 - 20) = 1.5 \times 4200 \times 80 = 504\,000\ \text{J}$
(b) [2] $P = 2.0\ \text{kW} = 2000\ \text{W}$, $t = \frac{Q}{P} = \frac{504\,000}{2000} = 252\ \text{s}$ (or 4 min 12 s)

18. [3 marks]

• Melt wax and let it cool, record temp vs time. [1]
• Plot cooling curve. [1]
• Flat portion indicates constant temp = melting point. [1]

19. [3 marks]
Heater warms air near floor. [1] Warm air rises (less dense). [1] Cool air sinks and is drawn to heater, forming convection current. [1]
Visual: Q19-fig1 shows loop.

20. [4 marks]
Heat lost by Al = heat gained by water
$m_{\text{Al}} c_{\text{Al}} (100 - T) = m_w c_w (T - 15)$
$0.30 \times 900 \times (100 - T) = 0.50 \times 4200 \times (T - 15)$
$270(100 - T) = 2100(T - 15)$
$27\,000 - 270T = 2100T - 31\,500$
$27\,000 + 31\,500 = 2370T$
$58\,500 = 2370T \Rightarrow T \approx 24.7\ ^\circ\text{C}$
Marking: 1 eqn, 1 expand, 1 solve, 1 answer.