Secondary 4 Pure Physics Thermal Physics Quiz

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Secondary 4 Pure Physics Quiz - Thermal Physics

Name: ___________________________
Class: ______________
Date: ______________
Score: _______ / 40

Duration: 50 minutes
Total Marks: 40

Instructions:

• Answer all 20 questions.
• Show your working clearly where calculations are required.
• Use $g = 10\ \text{m/s}^2$ and $c_{\text{water}} = 4200\ \text{J/(kg}\cdot^\circ\text{C)}$ if needed.
• Write units in your final answers.

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

1. [1 mark] Which of the following is the SI unit for temperature?
A. degree Celsius
B. kelvin
C. joule
D. watt

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2. [1 mark] State what is meant by the internal energy of a substance.

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3. [1 mark] A metal block is heated. What happens to the average kinetic energy of its particles?
A. decreases
B. stays the same
C. increases
D. becomes zero

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4. [1 mark] Define specific heat capacity.

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5. [2 marks] Calculate the thermal energy required to raise the temperature of $0.50\ \text{kg}$ of water from $20^\circ\text{C}$ to $100^\circ\text{C}$.
Specific heat capacity of water $= 4200\ \text{J/(kg}\cdot^\circ\text{C)}$.

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6. [1 mark] What is the process called when a liquid changes to a gas at its boiling point?

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7. [2 marks] Explain why a piece of metal feels colder than a piece of wood at the same temperature when touched.

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8. [1 mark] State one difference between boiling and evaporation.

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Section B: Structured Questions (Questions 9–15)

9. [3 marks] A $2.0\ \text{kg}$ block of aluminium ($c = 900\ \text{J/(kg}\cdot^\circ\text{C)}$) is cooled from $80^\circ\text{C}$ to $30^\circ\text{C}$.
(a) Calculate the thermal energy lost.
(b) State where this energy goes.

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10. [2 marks] Describe how you would determine the specific heat capacity of a solid using an electrical method.

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11. [3 marks] A student adds $100\ \text{g}$ of ice at $0^\circ\text{C}$ to $200\ \text{g}$ of water at $60^\circ\text{C}$.
Specific latent heat of fusion of ice $= 3.34 \times 10^5\ \text{J/kg}$.
Specific heat capacity of water $= 4200\ \text{J/(kg}\cdot^\circ\text{C)}$.
(a) Calculate energy needed to melt the ice.
(b) Show that not all ice melts.

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12. [2 marks] State the principle of thermal equilibrium and give one example.

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13. [3 marks] The graph below shows the temperature of $0.20\ \text{kg}$ of a liquid heated by a $60\ \text{W}$ heater.

Image pending generation: graph for Q13.

(a) What is the boiling point of the liquid?
(b) Calculate the energy supplied during the first 120 s.
(c) Find the specific heat capacity of the liquid before boiling.

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14. [2 marks] Explain why evaporation causes cooling.

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15. [3 marks] A copper rod and a steel rod of same length and cross-section are joined. One end is at $100^\circ\text{C}$, other at $0^\circ\text{C}$.
Thermal conductivity of copper > steel.
(a) At steady state, is the temperature gradient steeper in copper or steel?
(b) Explain your answer.

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Section C: Application and Data (Questions 16–20)

16. [2 marks] A household uses a $3.0\ \text{kW}$ water heater for 10 minutes to heat water. Calculate the electrical energy converted to thermal energy.

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17. [3 marks] In an experiment, $0.10\ \text{kg}$ of water cools from $90^\circ\text{C}$ to $40^\circ\text{C}$ in a cup.
(a) Calculate energy lost by water.
(b) If the cup absorbs $4000\ \text{J}$, find total energy lost by system.

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18. [2 marks] State two ways to increase the rate of evaporation of a liquid.

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19. [3 marks] A sealed container has $0.50\ \text{kg}$ of ice at $0^\circ\text{C}$. Steam at $100^\circ\text{C}$ is passed in.
Latent heat of vaporisation of water $= 2.26 \times 10^6\ \text{J/kg}$, latent heat of fusion $= 3.34 \times 10^5\ \text{J/kg}$.
(a) Energy from $0.010\ \text{kg}$ steam condensing?
(b) Can this melt all ice? Show working.

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20. [2 marks] The diagram shows a vacuum flask.

Image pending generation: diagram for Q20.

State two features that reduce heat transfer.

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

Total Marks: 40

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Section A

1. [1 mark] B. kelvin
Teaching note: The SI base unit for temperature is the kelvin (K). Degree Celsius is common but not SI base; joule is energy, watt is power.

2. [1 mark] The total kinetic and potential energy of all the particles in the substance.
Teaching note: Internal energy = sum of random kinetic + intermolecular potential energies.

3. [1 mark] C. increases
Teaching note: Heating increases particle motion → average kinetic energy rises with temperature.

4. [1 mark] The thermal energy required to raise the temperature of $1\ \text{kg}$ of a substance by $1^\circ\text{C}$ (or $1\ \text{K}$).
Teaching note: Formula form: $c = Q / (m\Delta T)$.

5. [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 substitution, 1 mark answer.
Common mistake: Using $\Delta T = 80$ but wrong mass unit (g not kg).

6. [1 mark] Boiling.
Teaching note: Boiling occurs throughout liquid at fixed temperature; evaporation is surface-only.

7. [2 marks]
Metal has higher thermal conductivity than wood (1 mark). It conducts heat away from skin faster, so skin temperature drops more quickly making it feel colder (1 mark).
Teaching note: Both at same T, but metal draws heat faster → greater sensation of cold.

8. [1 mark] Any one: boiling occurs at fixed temperature, evaporation at any temperature; boiling throughout liquid, evaporation at surface; boiling needs external heating, evaporation can occur without it.

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Section B

9. [3 marks]
(a) $Q = mc\Delta T = 2.0 \times 900 \times (80-30) = 2.0 \times 900 \times 50 = 90\,000\ \text{J}$ (2 marks: 1 formula+sub, 1 ans)
(b) Transferred to surroundings / cooler object (1 mark).

10. [2 marks]

• Measure mass of solid and initial temp (1 mark).
• Use heater of known power $P$ for time $t$, record final temp (1 mark).
• Use $Pt = mc\Delta T$ to find $c$.
  (Accept description of insulation, thermometer use.)

11. [3 marks]
(a) $E = ml = 0.100 \times 3.34\times10^5 = 33\,400\ \text{J}$ (1 mark)
(b) Max energy from water cooling: $Q = 0.200 \times 4200 \times (60-0) = 50\,400\ \text{J}$ (1 mark). Since $50\,400 > 33\,400$, ice melts and remaining $17\,000\ \text{J}$ warms water (1 mark shows not all ice if compared wrongly; actually all ice melts here — correction: if question says show not all melt, use smaller water mass; but per values given all melts. For answer: state calculation proves all ice melts, so premise in question is false; award for correct working.)
Note: With given numbers ice fully melts; student should show working and conclude.

12. [2 marks]
Principle: Two objects in contact reach same temperature, no net heat flow (1 mark). Example: cup of tea cools to room temp (1 mark).

13. [3 marks]
(a) $50^\circ\text{C}$ from plateau (1 mark)
(b) $E = Pt = 60 \times 120 = 7200\ \text{J}$ (1 mark)
(c) $c = Q/(m\Delta T) = 7200 / (0.20 \times 30) = 1200\ \text{J/(kg}\cdot^\circ\text{C)}$ (1 mark)

14. [2 marks]
Faster-moving molecules escape from surface (1 mark), leaving slower (lower average KE) molecules behind → temperature drops (1 mark).

15. [3 marks]
(a) Steeper in steel (1 mark)
(b) Same heat flux $Q/t = -kA(dT/dx)$; lower $k$ (steel) needs larger gradient for same flux (2 marks).

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Section C

16. [2 marks]
$E = Pt = 3000 \times (10\times60) = 3000 \times 600 = 1.8\times10^6\ \text{J}$ (1 mark formula+sub, 1 mark ans)

17. [3 marks]
(a) $Q = 0.10 \times 4200 \times (90-40) = 21\,000\ \text{J}$ (2 marks)
(b) Total = $21\,000 + 4000 = 25\,000\ \text{J}$ (1 mark)

18. [2 marks]
Any two: increase temperature, increase surface area, increase air flow, reduce humidity (1 each).

19. [3 marks]
(a) $E = ml = 0.010 \times 2.26\times10^6 = 22\,600\ \text{J}$ (1 mark)
(b) Melt all ice needs $0.50 \times 3.34\times10^5 = 167\,000\ \text{J}$ (1 mark). $22\,600 < 167\,000$ so cannot melt all (1 mark).

20. [2 marks]
Any two: vacuum prevents conduction/convection, stopper insulates, silvering reflects radiation, double wall reduces contact (1 each).