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A Level H2 Physics Thermal Physics Quiz

Free A Level H2 Physics Thermal Physics quiz, HY3 Exam version, with questions, answers, and A Level-style practice for Singapore students.

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Questions

A-Level Physics H2 Quiz - Thermal Physics

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

Duration: 60 minutes
Total Marks: 40

Instructions:

Answer all 20 questions.
Section A: Short structured questions (1–10). Section B: Data and calculation (11–15). Section C: Extended response (16–20).
Show all working where calculation is required.
Use $K = {}^\circ C + 273.15$ for temperature conversion unless stated.

Section A: Short Structured Questions (1–10) [12 marks]

1. State the thermodynamic temperature of $27.0\,^\circ\mathrm{C}$ in kelvin. [1]

2. Write the equation of state for an ideal gas in terms of number of molecules $N$ , using Boltzmann constant $k$ . [1]

3. State one key assumption of the kinetic theory of gases about the volume occupied by gas molecules. [1]

4. Define internal energy of a thermodynamic system. [1]

5. State the zeroth law of thermodynamics in one sentence. [1]

6. Write the first law of thermodynamics using the sign convention where $W$ is work done on the system. [1]

7. A gas expands at constant pressure $p$ . Write the expression for work done by the gas for volume change $\Delta V$ . [1]

8. Define specific heat capacity of a substance. [1]

9. State the unit of specific latent heat. [1]

10. The mean translational kinetic energy of a gas molecule is $\frac{3}{2}kT$ . State what the symbol $T$ represents. [1]

Section B: Data and Calculation (11–15) [15 marks]

11. A sealed flask contains $2.50 \times 10^{23}$ molecules of helium at $300\,\mathrm{K}$ . Calculate the pressure if the volume is $0.0200\,\mathrm{m^3}$ . ( $k = 1.38 \times 10^{-23}\,\mathrm{J\,K^{-1}}$ ) [3]

12. An ideal gas at $1.01 \times 10^5\,\mathrm{Pa}$ and $0.0500\,\mathrm{m^3}$ is compressed to $0.0200\,\mathrm{m^3}$ at constant temperature. Calculate the final pressure. [3]

13. A $1.20\,\mathrm{kg}$ block of copper ( $c = 390\,\mathrm{J\,kg^{-1}\,K^{-1}}$ ) cools from $80.0\,^\circ\mathrm{C}$ to $20.0\,^\circ\mathrm{C}$ . Calculate the heat lost. [3]

14. $0.0100\,\mathrm{kg}$ of ice at $0\,^\circ\mathrm{C}$ is converted to water at $0\,^\circ\mathrm{C}$ . Specific latent heat of fusion $= 3.34 \times 10^5\,\mathrm{J\,kg^{-1}}$ . Calculate the energy required. [3]

15. A gas is compressed. Work done on the gas is $+240\,\mathrm{J}$ and it loses $90\,\mathrm{J}$ as heat. Using $\Delta U = Q + W$ , calculate $\Delta U$ . [3]

Section C: Extended Response (16–20) [13 marks]

16. (a) State the basic assumptions of the kinetic theory of gases. [3]
(b) Explain how the pressure of a gas arises from molecular motion. [2]

17. Derive the relation $pV = \frac{1}{3}Nm\langle c^2\rangle$ from kinetic theory, stating any assumption used. [5]

18. A student heats $0.200\,\mathrm{kg}$ of water from $20.0\,^\circ\mathrm{C}$ to $100.0\,^\circ\mathrm{C}$ using a $500\,\mathrm{W}$ heater.
(a) Calculate the energy needed. ( $c_{\text{water}} = 4180\,\mathrm{J\,kg^{-1}\,K^{-1}}$ ) [2]
(b) Calculate the minimum time required. [2]

19. An ideal gas undergoes a cycle. In step 1, $400\,\mathrm{J}$ of heat enters and gas does $150\,\mathrm{J}$ of work. In step 2, $100\,\mathrm{J}$ of heat leaves and $200\,\mathrm{J}$ of work is done on the gas. Calculate the net change in internal energy over the cycle. [3]

20. The pressure-volume graph below shows a gas process.

Graph for Q20 (ALEVEL Physics H2)

Generated graph for Q20.

(a) Calculate work done by the gas from A to B. [2]
(b) State the total work done over the full cycle A→B→C→D→A. [1]

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Answers

A-Level Physics H2 Quiz - Thermal Physics (Answer Key)

Total Marks: 40
Duration: 60 minutes

Section A: Short Structured Questions (1–10)

1. [1 mark]
$T = 27.0 + 273.15 = 300.15\,\mathrm{K}$ (accept $300\,\mathrm{K}$ ).
Teaching: Thermodynamic (kelvin) temperature is Celsius + 273.15.

2. [1 mark]
$pV = NkT$
Teaching: $N$ = number of molecules, $k$ = Boltzmann constant.

3. [1 mark]
The volume of the gas molecules themselves is negligible compared with the volume of the container.
(Other valid: molecules are point particles / no intermolecular forces except during collisions.)

4. [1 mark]
Internal energy is the sum of the microscopic kinetic and potential energies of the molecules in the system.

5. [1 mark]
If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

6. [1 mark]
$\Delta U = Q + W$ (with $W$ = work done on system).

7. [1 mark]
Work done by gas = $p\Delta V$ (positive for expansion).

8. [1 mark]
Specific heat capacity is the energy required per unit mass to raise the temperature by 1 K (or $1\,^\circ\mathrm{C}$ ).

9. [1 mark]
$\mathrm{J\,kg^{-1}}$ (joules per kilogram).

10. [1 mark]
$T$ is the thermodynamic (absolute) temperature in kelvin.

Section B: Data and Calculation (11–15)

11. [3 marks]
$pV = NkT \Rightarrow p = \frac{NkT}{V}$
$= \frac{(2.50\times10^{23})(1.38\times10^{-23})(300)}{0.0200}$
$= \frac{1035}{0.0200} = 5.18\times10^{4}\,\mathrm{Pa}$
Mark breakdown: formula (1), substitution (1), answer + unit (1).

12. [3 marks]
Isothermal: $p_1V_1 = p_2V_2$
$p_2 = \frac{p_1V_1}{V_2} = \frac{(1.01\times10^5)(0.0500)}{0.0200} = 2.525\times10^5\,\mathrm{Pa}$
Marks: method (1), substitution (1), answer (1).

13. [3 marks]
$Q = mc\Delta\theta = 1.20 \times 390 \times (80.0-20.0)$
$= 1.20 \times 390 \times 60.0 = 2.81\times10^4\,\mathrm{J}$
Marks: formula (1), substitution (1), answer (1).

14. [3 marks]
$Q = ml = 0.0100 \times 3.34\times10^5 = 3.34\times10^3\,\mathrm{J}$
Marks: formula (1), substitution (1), answer (1).

15. [3 marks]
$Q = -90\,\mathrm{J}$ (lost), $W = +240\,\mathrm{J}$
$\Delta U = Q + W = -90 + 240 = +150\,\mathrm{J}$
Marks: sign of Q (1), sum (1), answer (1).

Section C: Extended Response (16–20)

16. [5 marks total]
(a) [3] Assumptions:

Large number of identical molecules in random motion.
Volume of molecules negligible.
No intermolecular forces except elastic collisions.
Collisions with walls and each other are perfectly elastic.
Duration of collision negligible; obey Newton’s laws.
(Any 3 clear points = 3 marks)
(b) [2] Pressure arises from repeated elastic collisions of molecules with container walls, delivering momentum change per unit time per unit area.

17. [5 marks]
Derivation:

Consider molecule mass $m$ , speed $c_x$ normal to wall of cube side $L$ .
Momentum change per collision = $2mc_x$ .
Time between collisions = $2L/c_x$ .
Force on wall = $\frac{2mc_x}{2L/c_x} = \frac{mc_x^2}{L}$ .
Pressure from one molecule: $p = \frac{mc_x^2}{L^3} = \frac{mc_x^2}{V}$ .
For $N$ molecules, average $\langle c_x^2\rangle = \frac{1}{3}\langle c^2\rangle$ .
$pV = \frac{1}{3}Nm\langle c^2\rangle$ .
Marks: setup (1), momentum (1), averaging (1), sum (1), final (1).

18. [4 marks]
(a) [2] $Q = mc\Delta\theta = 0.200 \times 4180 \times 80.0 = 6.69\times10^4\,\mathrm{J}$ .
(b) [2] $t = Q/P = 6.69\times10^4 / 500 = 134\,\mathrm{s}$ .
Marks: each part formula+answer.

19. [3 marks]
Step1: $\Delta U_1 = +400 - 150 = +250\,\mathrm{J}$ (work by gas = negative W on).
Step2: $\Delta U_2 = -100 + 200 = +100\,\mathrm{J}$ .
Net = $250 + 100 = +350\,\mathrm{J}$ .
Marks: each step (1+1), total (1).

20. [3 marks]
(a) [2] A→B isobaric expansion: $W = p\Delta V = (1.0\times10^5)(0.030-0.010) = 2.0\times10^3\,\mathrm{J}$ .
(b) [1] Total cycle work = area enclosed = rectangle = $(3.0-1.0)\times10^5 \times (0.030-0.010) = 4.0\times10^3\,\mathrm{J}$ done by gas.
Image must show labelled A,B,C,D and path; answer uses those values.