O Level Physics Thermal Physics Quiz

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O-Level Physics Quiz - Thermal Physics

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 50

Duration: 45 minutes
Total Marks: 50

Instructions:

1. Answer all questions.
2. Write your answers in the spaces provided.
3. Show all working for calculation questions.
4. Use $g = 10 \text{ m/s}^2$ where necessary.
5. Specific heat capacity of water $c_{water} = 4200 \text{ J/(kg}\cdot^\circ\text{C)}$.
6. Specific latent heat of fusion of ice $L_f = 334,000 \text{ J/kg}$.
7. Specific latent heat of vaporisation of water $L_v = 2,260,000 \text{ J/kg}$.

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Section A: Kinetic Particle Model & Thermal Processes (10 Marks)

1. Which statement correctly describes the arrangement and motion of particles in a liquid? [1]
A. Particles are closely packed in a regular lattice and vibrate about fixed positions.
B. Particles are far apart and move randomly at high speeds.
C. Particles are closely packed but can slide past one another.
D. Particles are arranged in layers and do not move.

Answer: __________________________

2. A student observes smoke particles under a microscope. The particles move in a random, zig-zag path. This phenomenon is known as Brownian motion.
What does this observation suggest about the air molecules surrounding the smoke particles? [2]

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3. Explain, in terms of particle motion, why the pressure of a fixed mass of gas increases when its temperature is increased while the volume remains constant. [3]

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4. Figure 4.1 shows a metal rod being heated at one end. Wax blobs are attached at intervals along the rod. The wax blobs melt from the heated end outwards.
Describe how thermal energy is transferred through the metal at the particle level. [2]

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5. A room is heated by an electric heater placed near the floor.
Explain why the heater is placed near the floor rather than the ceiling, referring to density and convection currents. [2]

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Section B: Thermal Properties of Matter (Calculations) (20 Marks)

6. Calculate the thermal energy required to raise the temperature of $2.5 \text{ kg}$ of water from $20^\circ\text{C}$ to $80^\circ\text{C}$. [3]
(Specific heat capacity of water = $4200 \text{ J/(kg}\cdot^\circ\text{C)}$)

<br> <br> <br> **Answer:** __________________________ J

7. A $500 \text{ W}$ immersion heater is placed in $0.5 \text{ kg}$ of oil. The temperature of the oil rises from $25^\circ\text{C}$ to $45^\circ\text{C}$ in $200 \text{ seconds}$.
Calculate the specific heat capacity of the oil. Assume no energy is lost to the surroundings. [3]

<br> <br> <br> **Answer:** __________________________ $\text{J/(kg}\cdot^\circ\text{C)}$

8. An ice cube of mass $0.02 \text{ kg}$ at $0^\circ\text{C}$ is placed into a drink.
Calculate the energy required to melt the ice cube completely at $0^\circ\text{C}$. [2]
(Specific latent heat of fusion of ice = $334,000 \text{ J/kg}$)

<br> <br> **Answer:** __________________________ J

9. After melting, the water from the ice (mass $0.02 \text{ kg}$) warms up from $0^\circ\text{C}$ to $10^\circ\text{C}$.
Calculate the additional energy absorbed by this water. [2]

<br> <br> **Answer:** __________________________ J

10. A student performs an experiment to determine the specific latent heat of vaporisation of water.

• Mass of water boiled away = $0.05 \text{ kg}$
• Power of heater = $2000 \text{ W}$
• Time taken = $60 \text{ s}$

Calculate the experimental value for the specific latent heat of vaporisation of water. [2]

<br> <br> **Answer:** __________________________ $\text{J/kg}$

11. Block A has a mass of $2 \text{ kg}$ and a specific heat capacity of $900 \text{ J/(kg}\cdot^\circ\text{C)}$. Block B has a mass of $4 \text{ kg}$ and a specific heat capacity of $450 \text{ J/(kg}\cdot^\circ\text{C)}$.
Both blocks are supplied with the same amount of thermal energy.
Compare the temperature rise of Block A to the temperature rise of Block B and explain your answer. [2]

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12. An electric kettle supplies $150,000 \text{ J}$ of energy to boil water. If $0.06 \text{ kg}$ of water is turned into steam, calculate the specific latent heat of vaporisation determined from this experiment. [2]

<br> <br> **Answer:** __________________________ $\text{J/kg}$

13. A $2 \text{ kg}$ block of copper ($c = 385 \text{ J/(kg}\cdot^\circ\text{C)}$) is heated from $20^\circ\text{C}$ to $70^\circ\text{C}$.
Calculate the thermal energy supplied to the copper block. [2]

<br> <br> **Answer:** __________________________ J

14. A $100 \text{ W}$ heater is used to melt $0.05 \text{ kg}$ of ice at $0^\circ\text{C}$.
Calculate the minimum time required to melt the ice completely. [2]
(Specific latent heat of fusion of ice = $334,000 \text{ J/kg}$)

<br> <br> **Answer:** __________________________ s

15. $500 \text{ g}$ of water cools from $80^\circ\text{C}$ to $30^\circ\text{C}$.
Calculate the energy lost by the water. [2]

<br> <br> **Answer:** __________________________ J

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Section C: Structured Questions & Applications (20 Marks)

16. Figure 16.1 shows a cooling curve for a pure substance being cooled from a gas to a solid. The temperature remains constant at $0^\circ\text{C}$ for a period of time.
Explain why the temperature remains constant at $0^\circ\text{C}$ even though the substance is losing energy to the surroundings. [2]

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17. During the plateau at $0^\circ\text{C}$ in the cooling curve mentioned in Q16, describe the change in the internal energy of the substance. Refer to kinetic and potential energy of particles. [2]

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18. Double-glazed windows consist of two sheets of glass with a layer of air between them.
(a) Explain how the layer of air reduces thermal energy loss by conduction. [1]

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(b) Explain how the layer of air reduces thermal energy loss by convection. [1]

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19. Some double-glazed windows have a shiny metallic coating on one surface.
Explain how this reduces thermal energy loss by radiation. [2]

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20. Evaporation causes cooling.
(a) Explain, in terms of particle energy, why evaporation causes the remaining liquid to cool down. [2]

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(b) State two factors that increase the rate of evaporation. [2]

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O-Level Physics Quiz - Thermal Physics (Answer Key)

1. C
Reasoning: In liquids, particles are close together (incompressible) but have enough energy to overcome fixed lattice positions, allowing them to flow/slide. A is solid, B is gas.

2.
Air molecules are in constant, random motion [1]. They collide with the larger smoke particles from different directions, causing the erratic movement [1].

3.

• As temperature increases, the average kinetic energy of the gas particles increases [1].
• The particles move faster and collide with the walls of the container more frequently [1].
• The collisions are also harder (greater change in momentum), resulting in a greater force per unit area (pressure) [1].

4.
Free electrons in the metal gain kinetic energy and move through the lattice, colliding with atoms/ions [1]. The atoms/ions also vibrate more vigorously and pass this vibration to neighboring atoms [1].

5.
Air near the heater warms up, expands, and becomes less dense [1]. The warm, less dense air rises, while cooler, denser air sinks to replace it, setting up a convection current that heats the whole room [1].

6.
Formula: $E = mc\Delta\theta$ [1]
Substitution: $E = 2.5 \times 4200 \times (80 - 20)$ [1]
Calculation: $E = 2.5 \times 4200 \times 60 = 630,000 \text{ J}$ [1]
Answer: 630,000 J

7.
Energy Supplied: $E = P \times t = 500 \times 200 = 100,000 \text{ J}$ [1]
Formula: $c = E / (m\Delta\theta)$ [1]
Calculation: $c = 100,000 / (0.5 \times 20) = 10,000 \text{ J/(kg}\cdot^\circ\text{C)}$ [1]
Answer: 10,000 J/(kg·°C)

8.
Formula: $E = mL_f$ [1]
Calculation: $E = 0.02 \times 334,000 = 6,680 \text{ J}$ [1]
Answer: 6,680 J

9.
Formula: $E = mc\Delta\theta$ [1]
Calculation: $E = 0.02 \times 4200 \times 10 = 840 \text{ J}$ [1]
Answer: 840 J

10.
Energy Supplied: $E = P \times t = 2000 \times 60 = 120,000 \text{ J}$ [1]
Formula: $L_v = E / m$ [1]
Calculation: $L_v = 120,000 / 0.05 = 2,400,000 \text{ J/kg}$
Answer: 2,400,000 J/kg

11.
For A: Thermal Capacity $mc = 2 \times 900 = 1800 \text{ J/}^\circ\text{C}$
For B: Thermal Capacity $mc = 4 \times 450 = 1800 \text{ J/}^\circ\text{C}$
Since the thermal capacity is the same for both, and energy $E$ is the same, the temperature rise is the same [1].
Explanation: Both blocks have the same thermal capacity [1].

12.
Formula: $L_v = E / m$ [1]
Calculation: $L_v = 150,000 / 0.06 = 2,500,000 \text{ J/kg}$ [1]
Answer: 2,500,000 J/kg

13.
Formula: $E = mc\Delta\theta$ [1]
Calculation: $E = 2 \times 385 \times (70 - 20) = 2 \times 385 \times 50 = 38,500 \text{ J}$ [1]
Answer: 38,500 J

14.
Energy Required: $E = mL_f = 0.05 \times 334,000 = 16,700 \text{ J}$ [1]
Time: $t = E / P = 16,700 / 100 = 167 \text{ s}$ [1]
Answer: 167 s

15.
Mass $m = 0.5 \text{ kg}$
Formula: $E = mc\Delta\theta$ [1]
Calculation: $E = 0.5 \times 4200 \times (80 - 30) = 0.5 \times 4200 \times 50 = 105,000 \text{ J}$ [1]
Answer: 105,000 J

16.
Energy is being released to form bonds between particles (change in potential energy) rather than decreasing kinetic energy [1]. Since temperature is a measure of average kinetic energy, and KE is constant during phase change, temperature remains constant [1].

17.
Kinetic energy remains constant (temperature is constant) [1]. Potential energy decreases as particles move closer together into a more ordered solid structure [1].

18.
(a) Air is a poor conductor of heat (good insulator) [1].
(b) The gap is narrow, preventing large convection currents from forming [1].

19.
Shiny surfaces are poor emitters of infrared radiation [1]. This reduces the amount of heat radiated from the inner glass to the outer glass [1].

20.
(a) Only particles with high kinetic energy near the surface have enough energy to escape the liquid [1]. When these high-energy particles leave, the average kinetic energy of the remaining particles decreases, lowering the temperature [1].
(b) Any two of:

1. Higher temperature [1]
2. Larger surface area [1]
3. Air flow/draught over the surface [1]
4. Lower humidity [1]