Secondary 4 Pure Physics Thermal Physics Quiz

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Secondary 4 Pure Physics Quiz - Thermal Physics

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

Duration: 60 Minutes
Total Marks: 50

Instructions:

• Answer all questions.
• For calculation questions, show all working clearly.
• Use $g = 10\text{ m/s}^2$ where applicable.
• Specific heat capacity of water = $4200\text{ J/kg}\cdot\text{K}$.

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Section A: Kinetic Particle Model & Thermal Processes (Questions 1-7)

1. State the three states of matter and describe the arrangement of particles in a solid. [2]
   
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2. Brownian motion is often cited as evidence for the kinetic particle model. Explain what Brownian motion is and what it proves about particles. [3]
   
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3. A gas is contained in a sealed metallic cylinder. Explain, in terms of the kinetic particle model, how the pressure of the gas is exerted on the walls of the cylinder. [3]
   
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4. Compare the process of conduction in a metal to conduction in a non-metal (insulator). [3]
   
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5. Explain why a convection current forms in a beaker of water being heated from the bottom. [3]
   
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6. A person wearing a black woollen sweater feels warmer in the sun than a person wearing a white silk shirt. Explain this observation with reference to thermal radiation. [3]
   
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7. Describe the condition required for two objects to be in thermal equilibrium. [2]
   
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Section B: Thermal Properties of Matter (Questions 8-15)

8. Define "internal energy" of a substance. [2]
   
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9. A 0.4 kg block of aluminum is heated from $25^\circ\text{C}$ to $75^\circ\text{C}$. If the specific heat capacity of aluminum is $900\text{ J/kg}\cdot\text{K}$, calculate the thermal energy absorbed. [3]
   
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10. Distinguish between boiling and evaporation. State two differences. [3]
    
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11. Explain why the temperature of a substance remains constant during the process of melting, even though thermal energy is still being supplied. [3]
    
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12. An ice cube of mass 0.05 kg at $0^\circ\text{C}$ is completely melted into water at $0^\circ\text{C}$. Given the specific latent heat of fusion of ice is $3.34 \times 10^5\text{ J/kg}$, calculate the energy required. [3]
    
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13. A 0.2 kg sample of water at $100^\circ\text{C}$ is converted to steam at $100^\circ\text{C}$. If the specific latent heat of vaporization of water is $2.26 \times 10^6\text{ J/kg}$, calculate the energy absorbed. [3]
    
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14. A student observes a cooling curve of a liquid. The graph shows a horizontal plateau before the temperature begins to drop again. What physical process is occurring during this plateau? Explain using the particle model. [4]
    
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15. A metal bolt is heated and then dropped into a beaker of cool water. Describe the energy transfer that occurs until the bolt and water reach the same temperature. [3]
    
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Section C: Synthesis & Application (Questions 16-20)

16. A thermos flask has a double-walled glass vessel with a vacuum between the walls and a silvered inner surface. Explain how these two features reduce heat loss. [4]
    
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17. A 0.5 kg piece of copper at $100^\circ\text{C}$ is placed into 1.0 kg of water at $20^\circ\text{C}$. Calculate the final equilibrium temperature. (Specific heat capacity of copper = $390\text{ J/kg}\cdot\text{K}$, water = $4200\text{ J/kg}\cdot\text{K}$). [5]
    
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18. Explain why a breeze often blows from the sea towards the land during a hot sunny day (sea breeze). [4]
    
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19. Compare the energy required to raise the temperature of 1 kg of water by $10^\circ\text{C}$ versus the energy required to melt 1 kg of ice at $0^\circ\text{C}$. Which is greater? Justify your answer with calculations. [5]
    
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20. Using the kinetic particle model, explain why the pressure of a fixed mass of gas in a closed container increases when the container is heated. [3]
    
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Secondary 4 Pure Physics Quiz - Thermal Physics (Answer Key)

Section A: Kinetic Particle Model & Thermal Processes

1. States: Solid, Liquid, Gas. Arrangement: Particles in a solid are closely packed in a regular lattice/fixed positions. [2]
2. Brownian Motion: The random, erratic movement of small particles (e.g., pollen/smoke) suspended in a fluid. Proof: It proves that the fluid consists of tiny particles in constant, random motion that collide with the larger particles. [3]
3. Gas Pressure: Gas particles move randomly at high speeds. They collide with the walls of the cylinder. Each collision exerts a small force on the wall. The sum of these forces over a unit area results in pressure. [3]
4. Conduction: In metals, heat is conducted via lattice vibrations AND free electrons (faster). In non-metals, heat is conducted only via lattice vibrations (slower). [3]
5. Convection: Water at the bottom is heated $\rightarrow$ expands $\rightarrow$ becomes less dense $\rightarrow$ rises. Cooler, denser water from the top sinks to replace it, creating a cycle. [3]
6. Radiation: Black/dark surfaces are better absorbers of infrared radiation than white/light surfaces. Wool is a poor conductor (traps air), further reducing heat loss. The black sweater absorbs more solar energy. [3]
7. Thermal Equilibrium: Two objects are in thermal equilibrium when they are at the same temperature and there is no net flow of thermal energy between them. [2]

Section B: Thermal Properties of Matter

8. Internal Energy: The sum of the random distribution of kinetic energy and potential energy of the particles in a system. [2]
9. $Q = mc\Delta\theta = 0.4 \times 900 \times (75 - 25) = 0.4 \times 900 \times 50 = 18,000\text{ J}$. [3]
10. Boiling: Occurs throughout the liquid; occurs at a fixed boiling point. Evaporation: Occurs only at the surface; occurs at any temperature below the boiling point. [3]
11. Melting: Thermal energy is used to break/overcome the attractive forces (bonds) between particles to change the state from solid to liquid. No increase in average kinetic energy occurs, so temperature remains constant. [3]
12. $Q = mL = 0.05 \times 3.34 \times 10^5 = 16,700\text{ J}$. [3]
13. $Q = mL = 0.2 \times 2.26 \times 10^6 = 452,000\text{ J}$. [3]
14. Process: Freezing (liquid to solid). Explanation: Thermal energy is being released as particles form bonds to create a regular lattice. The release of latent heat offsets the cooling, keeping the temperature constant. [4]
15. Thermal energy flows from the hot bolt (higher temperature) to the cool water (lower temperature) via conduction. This continues until both reach the same temperature (thermal equilibrium). [3]

Section C: Synthesis & Application

16. Vacuum: Prevents heat loss by conduction and convection (as these require a medium). Silvered surface: Reduces heat loss by radiation (silver is a poor emitter/good reflector of IR). [4]
17. Heat lost by copper = Heat gained by water. $m_c c_c (100 - T) = m_w c_w (T - 20)$ $0.5 \times 390 \times (100 - T) = 1.0 \times 4200 \times (T - 20)$ $195(100 - T) = 4200(T - 20)$ $19500 - 195T = 4200T - 84000$ $103500 = 4395T \rightarrow T \approx 23.5^\circ\text{C}$. [5]
18. Land heats up faster than the sea. Air above land becomes hot, expands, and rises. Cooler, denser air from the sea moves in to replace the rising air, creating a sea breeze. [4]
19. Water heating: $Q = 1 \times 4200 \times 10 = 42,000\text{ J}$. Ice melting: $Q = 1 \times 3.34 \times 10^5 = 334,000\text{ J}$. Melting 1 kg of ice requires significantly more energy. [5]
20. Heating increases the average kinetic energy of particles $\rightarrow$ particles move faster $\rightarrow$ they collide with walls more frequently and with greater force $\rightarrow$ pressure increases. [3]