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Secondary 3 Physics Thermal Physics Quiz

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Questions

Secondary 3 Physics Quiz - Thermal Physics

Name: ____________________ Class: __________ Date: __________ Score: ________ / 45

Duration: 60 Minutes
Total Marks: 45
Instructions: Answer all questions. Show all working for calculations. Use $g = 10\text{ m s}^{-2}$ where applicable.

Section A: Multiple Choice (10 Marks)

Circle the most appropriate option.

Which of the following is the best evidence for the existence of molecules in a gas? A. The expansion of a metal rod when heated. B. The random motion of smoke particles in air. C. The boiling of water at $100^\circ\text{C}$ . D. The conduction of heat through a copper wire. [1]
A gas is held in a sealed container. If the temperature of the gas increases, what happens to the pressure? A. Decreases, because particles move slower. B. Increases, because particles collide with walls more frequently and with greater force. C. Remains constant, because the volume is fixed. D. Increases, because the particles expand in size. [1]
Which statement correctly describes the process of conduction in a metal? A. Only through the vibration of atoms. B. Through the movement of free electrons and atomic vibrations. C. Through the movement of fluid particles. D. Through the emission of infrared radiation. [1]
A shiny silver surface is a better ___________ of thermal radiation than a dull black surface. A. Absorber B. Emitter C. Reflector D. Conductor [1]
Which of the following occurs during the melting of a solid? A. The average kinetic energy of the particles increases. B. The temperature of the substance increases. C. The potential energy of the particles increases. D. The particles stop moving entirely. [1]
The specific heat capacity of a substance is defined as the energy required to: A. Change the state of 1 kg of the substance. B. Raise the temperature of 1 kg of the substance by $1^\circ\text{C}$ . C. Raise the temperature of the entire mass by $1\text{ K}$ . D. Melt 1 kg of the substance. [1]
Which of the following is a characteristic of evaporation? A. It occurs only at the boiling point. B. It occurs throughout the entire volume of the liquid. C. It results in the cooling of the remaining liquid. D. It requires the addition of external heat to occur. [1]
Two objects are in thermal equilibrium when: A. They have the same mass. B. There is no net heat transfer between them. C. They are both at $0^\circ\text{C}$ . D. They are made of the same material. [1]
Which of the following is the correct SI unit for specific latent heat? A. $\text{J kg}^{-1}\text{ K}^{-1}$ B. $\text{J kg}^{-1}$ C. $\text{W kg}^{-1}$ D. $\text{J K}^{-1}$ [1]
In a convection current in a liquid, the warmer region: A. Becomes denser and sinks. B. Becomes less dense and rises. C. Remains at the same density. D. Moves only horizontally. [1]

Section B: Structured Questions (35 Marks)

(a) State the relationship between the temperature of a gas and the average kinetic energy of its particles. [1]

(b) Using the kinetic particle model, explain why the pressure of a gas increases when it is heated at a constant volume. [2]
A copper block of mass $0.5\text{ kg}$ is heated to $150^\circ\text{C}$ and then placed into a beaker containing $0.2\text{ kg}$ of water at $25^\circ\text{C}$ . (a) Calculate the thermal energy gained by the water if the final equilibrium temperature is $35^\circ\text{C}$ . (Specific heat capacity of water = $4200\text{ J kg}^{-1}\text{ }^\circ\text{C}^{-1}$ ) [2]

(b) Calculate the specific heat capacity of the copper block, assuming no heat is lost to the surroundings. [2]
(a) Describe how heat is transferred from a hot plate to a pot of water via convection. [2]

(b) Explain why a vacuum flask has silvered inner walls. [2]
An electric kettle contains $1.5\text{ kg}$ of water at $20^\circ\text{C}$ . The kettle is powered by a $2000\text{ W}$ heater. (a) Calculate the energy required to bring the water to its boiling point ( $100^\circ\text{C}$ ). [2]

(b) Calculate the minimum time required for the water to reach boiling point. [2]
A sample of ice of mass $0.1\text{ kg}$ at $0^\circ\text{C}$ is heated until it becomes water at $20^\circ\text{C}$ . (a) Calculate the energy required to melt the ice. (Specific latent heat of fusion of ice = $3.34 \times 10^5\text{ J kg}^{-1}$ ) [2]

(b) Calculate the additional energy required to raise the temperature of the resulting water to $20^\circ\text{C}$ . [2]
(a) Distinguish between boiling and evaporation. [2]

(b) Explain why sweating helps to cool the human body. [2]
A $1200\text{ W}$ immersion heater is used to boil $0.8\text{ kg}$ of water initially at $30^\circ\text{C}$ . (a) Calculate the time taken to reach $100^\circ\text{C}$ . [2]

(b) If the heater continues to operate for another 5 minutes after boiling starts, calculate the mass of water that is converted to steam. (Specific latent heat of vaporization of water = $2.26 \times 10^6\text{ J kg}^{-1}$ ) [3]
A metal rod is heated at one end. (a) Describe the process of conduction in terms of particles. [2]

(b) Why are the handles of cooking pans usually made of plastic or wood? [2]
(a) Define internal energy. [2]

(b) When a substance changes state from liquid to gas at a constant temperature, what happens to its internal energy? Explain your answer. [2]
A graph of temperature vs. time for a cooling liquid shows a horizontal plateau. (a) What is happening to the substance during this plateau? [1]

(b) Explain why the temperature does not drop even though the substance is still losing heat to the surroundings. [2]

Answers

Secondary 3 Physics Quiz - Thermal Physics (Answer Key)

Section A: Multiple Choice

B - Brownian motion is the direct evidence for molecular movement.
B - Higher temp $\rightarrow$ higher KE $\rightarrow$ more frequent/forceful collisions.
B - Metals conduct via both lattice vibrations and free electron drift.
C - Shiny surfaces reflect most radiation.
C - During melting, energy breaks bonds (increases PE), temperature (KE) stays constant.
B - Definition of specific heat capacity.
C - Most energetic particles leave, lowering the average KE of the rest.
B - Definition of thermal equilibrium.
B - $\text{J/kg}$ (Energy per unit mass).
B - Heating $\rightarrow$ expansion $\rightarrow$ lower density $\rightarrow$ rises.

Section B: Structured Questions

(a) Temperature is directly proportional to the average kinetic energy of the particles. [1] (b) Particles move faster $\rightarrow$ collide with walls more frequently [1] and with greater force [1].
(a) $Q = mc\Delta\theta = 0.2 \times 4200 \times (35 - 25) = 8,400\text{ J}$ [2] (b) $Q_{\text{lost by copper}} = Q_{\text{gained by water}} = 8,400\text{ J}$ $c = Q / (m\Delta\theta) = 8,400 / (0.5 \times (150 - 35)) = 8,400 / 57.5 \approx 146.1\text{ J kg}^{-1}\text{ }^\circ\text{C}^{-1}$ [2]
(a) Water at the bottom is heated, expands, becomes less dense and rises [1]. Cooler, denser water sinks to take its place, creating a convection current [1]. (b) Silvered walls are poor emitters and poor absorbers [1], they reflect thermal radiation back into the flask to minimize heat loss [1].
(a) $Q = 1.5 \times 4200 \times (100 - 20) = 504,000\text{ J}$ [2] (b) $t = E / P = 504,000 / 2000 = 252\text{ s}$ (or 4.2 mins) [2]
(a) $Q = mL = 0.1 \times 3.34 \times 10^5 = 33,400\text{ J}$ [2] (b) $Q = mc\Delta\theta = 0.1 \times 4200 \times (20 - 0) = 8,400\text{ J}$ [2]
(a) Boiling occurs throughout the liquid at a fixed temperature [1]; evaporation occurs only at the surface at any temperature [1]. (b) Sweat evaporates from the skin [1], absorbing latent heat from the body, which lowers the body temperature [1].
(a) $Q = 0.8 \times 4200 \times (100 - 30) = 235,200\text{ J}$ . $t = 235,200 / 1200 = 196\text{ s}$ [2] (b) Total energy in 5 mins = $1200 \times 300 = 360,000\text{ J}$ [1] $m = Q / L = 360,000 / (2.26 \times 10^6) \approx 0.159\text{ kg}$ [2]
(a) Particles at the hot end vibrate more vigorously and collide with neighbors [1], transferring energy along the rod [1]. (b) Plastic/wood are insulators [1] (low thermal conductivity), preventing heat from reaching the hand [1].
(a) The sum of the random kinetic and potential energies of all the particles in a substance. [2] (b) Internal energy increases [1]. Energy is used to break/weaken intermolecular bonds (increasing potential energy) while kinetic energy remains constant [1].
(a) The substance is changing state (freezing/solidifying). [1] (b) Heat is being released as particles form bonds [1], which compensates for the heat lost to the surroundings, keeping the temperature constant [1].