A Level H1 Physics Thermal Physics Quiz

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A-Level Physics H1 Quiz - Thermal Physics

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 55

Duration: 60 Minutes
Total Marks: 55

Instructions:

• Answer all questions in the spaces provided.
• Use $g = 9.81 \text{ m s}^{-2}$ where applicable.
• Show all working clearly for calculation questions.

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Section A: Conceptual Understanding (Questions 1–8)

1. Define the term internal energy of a system. [2]
   
   
   
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2. Explain why the temperature of a substance remains constant during a phase change, such as melting. [2]
   
   
   
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3. State the conditions under which the ideal gas law $PV = nRT$ is most applicable. [2]
   
   
   
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4. A gas is compressed isothermally. Describe what happens to the average kinetic energy of the gas molecules. [2]
   
   
   
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5. Distinguish between specific heat capacity and specific latent heat. [2]
   
   
   
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6. Explain the relationship between the pressure of an ideal gas and the collisions of molecules with the container walls. [2]
   
   
   
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7. Why does a real gas deviate from ideal behavior at very high pressures? [2]
   
   
   
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8. Describe the process of evaporation and how it differs from boiling. [2]
   
   
   
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Section B: Application and Calculation (Questions 9–16)

9. A $0.50\text{ kg}$ block of aluminum (specific heat capacity $900\text{ J kg}^{-1}\text{ K}^{-1}$) is heated from $20^\circ\text{C}$ to $80^\circ\text{C}$. Calculate the energy supplied. [3]
   
   
   
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10. An ideal gas is contained in a cylinder with a movable piston. If the volume is halved while the temperature is kept constant, determine the new pressure if the initial pressure was $1.0 \times 10^5\text{ Pa}$. [3]
    
    
    
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11. Calculate the number of moles of an ideal gas that occupies $2.4\text{ m}^3$ at a pressure of $1.0 \times 10^5\text{ Pa}$ and a temperature of $27^\circ\text{C}$. ($R = 8.31\text{ J mol}^{-1}\text{ K}^{-1}$) [3]
    
    
    
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12. A $20\text{ g}$ piece of ice at $0^\circ\text{C}$ is heated until it becomes water at $20^\circ\text{C}$. Calculate the total energy required. (Specific latent heat of fusion of ice $= 3.34 \times 10^5\text{ J kg}^{-1}$; Specific heat capacity of water $= 4180\text{ J kg}^{-1}\text{ K}^{-1}$) [4]
    
    
    
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13. A sample of gas has a root-mean-square (r.m.s.) speed of $v$. If the absolute temperature is increased by a factor of 4, determine the new r.m.s. speed in terms of $v$. [3]
    
    
    
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14. A copper sphere of mass $0.20\text{ kg}$ at $100^\circ\text{C}$ is dropped into $0.50\text{ kg}$ of water at $20^\circ\text{C}$. Calculate the final equilibrium temperature. (Specific heat capacity of copper $= 390\text{ J kg}^{-1}\text{ K}^{-1}$; water $= 4180\text{ J kg}^{-1}\text{ K}^{-1}$) [4]
    
    
    
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15. A gas undergoes an adiabatic expansion. Explain why the temperature of the gas decreases during this process. [3]
    
    
    
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16. A $1.0\text{ m}^3$ container holds an ideal gas at $300\text{ K}$ and $1.0 \times 10^5\text{ Pa}$. If the gas is heated to $600\text{ K}$ at constant pressure, calculate the new volume. [3]
    
    
    
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Section C: Synthesis and Analysis (Questions 17–20)

17. (a) State the First Law of Thermodynamics. [1] (b) A system does $200\text{ J}$ of work while $500\text{ J}$ of heat is added to it. Calculate the change in internal energy. [2]
    
    
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18. Compare the molecular motion of a substance in the solid, liquid, and gaseous states. How does this relate to the concept of potential energy? [4]
    
    
    
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19. A graph of pressure $P$ against volume $V$ for a gas is shown as a curve. If the process is isothermal, derive the expression for the gradient of the graph of $\ln P$ against $\ln V$. [4]
    
    
    
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20. Explain the "cooling effect" of a refrigerant in a fridge, referring to the relationship between pressure, temperature, and phase changes. [5]
    
    
    
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A-Level Physics H1 Quiz - Thermal Physics (Answer Key)

1. Internal Energy: The sum of the random distribution of kinetic and potential energies associated with the molecules of a system. [2]

2. Constant Temperature during Phase Change: Energy is used to overcome the intermolecular forces of attraction (increasing potential energy) rather than increasing the average kinetic energy of the molecules. [2]

3. Ideal Gas Conditions: Low pressure and high temperature (where intermolecular forces are negligible and molecular volume is small compared to container volume). [2]

4. Isothermal Compression: The average kinetic energy remains constant because temperature is constant ($T \propto \text{avg KE}$). [2]

5. SHC vs SLH: Specific heat capacity is the energy required to raise the temperature of $1\text{ kg}$ by $1\text{ K}$. Specific latent heat is the energy required to change the phase of $1\text{ kg}$ without a change in temperature. [2]

6. Pressure and Collisions: Pressure is the result of the change in momentum of gas molecules as they collide with the walls per unit area per unit time. [2]

7. Real Gas Deviation: At high pressures, the volume of the molecules themselves becomes significant, and intermolecular attractive forces start to act, reducing the impact force on walls. [2]

8. Evaporation vs Boiling: Evaporation occurs only at the surface and at any temperature; boiling occurs throughout the liquid and only at a specific boiling point. [2]

9. $Q = mc\Delta T = 0.50 \times 900 \times (80 - 20) = 0.50 \times 900 \times 60 = 27,000\text{ J}$ or $2.7 \times 10^4\text{ J}$. [3]

10. $P_1V_1 = P_2V_2 \rightarrow (1.0 \times 10^5) \times V = P_2 \times (0.5V) \rightarrow P_2 = 2.0 \times 10^5\text{ Pa}$. [3]

11. $PV = nRT \rightarrow n = PV/RT = (1.0 \times 10^5 \times 2.4) / (8.31 \times (273 + 27)) = 240,000 / (8.31 \times 300) = 240,000 / 2493 \approx 96.3\text{ mol}$. [3]

12. $Q_{\text{total}} = m L_f + mc\Delta T = (0.020 \times 3.34 \times 10^5) + (0.020 \times 4180 \times 20) = 6680 + 1672 = 8352\text{ J}$. [4]

13. $v_{\text{rms}} \propto \sqrt{T}$. If $T$ increases by factor of 4, $v_{\text{new}} = \sqrt{4} \times v = 2v$. [3]

14. Heat lost by copper = Heat gained by water. $0.20 \times 390 \times (100 - T) = 0.50 \times 4180 \times (T - 20)$ $78(100 - T) = 2090(T - 20)$ $7800 - 78T = 2090T - 41800$ $2168T = 49600 \rightarrow T \approx 22.9^\circ\text{C}$. [4]

15. In an adiabatic expansion, no heat enters/leaves the system ($Q=0$). The gas does work on the surroundings, and this energy comes from the internal energy of the gas, leading to a decrease in temperature. [3]

16. $V_1/T_1 = V_2/T_2 \rightarrow 1.0/300 = V_2/600 \rightarrow V_2 = 2.0\text{ m}^3$. [3]

17. (a) $\Delta U = Q - W$ (Change in internal energy = heat added minus work done by system). [1] (b) $\Delta U = 500 - 200 = 300\text{ J}$. [2]

18. Solid: Fixed positions, vibrate. Liquid: Close but slide. Gas: Random, far apart. Potential energy is lowest in solids (strongest bonds) and highest in gases (negligible bonds). [4]

19. $PV = \text{constant} \rightarrow P = C V^{-1}$ $\ln P = \ln C - \ln V$ $\ln P = -1(\ln V) + \ln C$ Gradient = $-1$. [4]

20. Refrigerant evaporates at low pressure (absorbing heat from food/air), then is compressed to high pressure (increasing temperature), and releases heat to the surroundings via a condenser. [5]