IGCSE Physics Paper 4 (Theory/Extended) - Mock 2

Topic 2: Thermal Physics | Core + Supplement

Duration 75 minutes

Total Marks 80

Questions 7

Time Remaining 75:00

Instructions

Answer ALL questions in the spaces provided.
Show all working for calculation questions. Marks are awarded for method even if the final answer is incorrect.
Specific heat capacity of water = 4200 J/(kg C) unless stated otherwise.
Specific heat capacity of aluminium = 900 J/(kg C) unless stated otherwise.
Your answers will be automatically graded when you submit the exam. The model answers will be shown for review.

Question Navigation Score: 0 / 80

Question 1: Particle Model and Brownian Motion

Total: 12 marks

(a) 6 marks

Coconut oil is a substance that is solid at 20 °C but melts at 24 °C and boils at 351 °C.

(a) (i) 3 marks

Model Answer - Q1(a)(i)

Particles are closely packed in a regular/fixed pattern [1]

Particles are very close together with very small separation between them [1]

Particles vibrate about fixed positions; they do not move from place to place [1]

Mark 1: Regular/fixed pattern arrangement

Mark 2: Very close together / small separation

Mark 3: Vibrate about fixed positions

(a) (ii) 3 marks

Model Answer - Q1(a)(ii)

Particles are randomly arranged with no fixed pattern (unlike the regular arrangement in a solid) [1]

Particles are very far apart with large separation between them (much further apart than in a solid) [1]

Particles move rapidly in all directions / random motion at high speed (instead of vibrating in fixed positions) [1]

Mark 1: Random arrangement / no fixed pattern

Mark 2: Far apart / large separation

Mark 3: Rapid random motion in all directions

(b) 4 marks

A student observes pollen grains suspended in water using a microscope. The pollen grains are seen to move in a random, jerky path.

(b) (i) 1 mark

Model Answer - Q1(b)(i)

Brownian motion [1]

Mark 1: Brownian motion

(b) (ii) 3 marks

Model Answer - Q1(b)(ii)

The water molecules are in constant random motion [1]

The water molecules collide with / bombard the pollen grains [1]

The uneven / unbalanced bombardment from different sides causes the pollen grains to change direction randomly [1]

Mark 1: Water molecules are in constant random motion

Mark 2: Water molecules collide with / bombard the pollen grains

Mark 3: Uneven bombardment causes random direction changes

The student heats the water containing the pollen grains. Describe and explain how the motion of the pollen grains changes.

Model Answer - Q1(c)

The pollen grains move faster / more vigorously [1]

Because the water molecules gain more kinetic energy at higher temperature, so they hit the pollen grains harder / more frequently [1]

Mark 1: Pollen grains move faster / more vigorously

Mark 2: Water molecules have more KE / hit harder or more often

Question 2: Gas Pressure, Boyle's Law and Temperature

Total: 11 marks

(a) 3 marks

A sealed bicycle tyre contains air at high pressure. Using the kinetic particle model, explain how the gas molecules inside the tyre exert pressure on the tyre walls.

Model Answer - Q2(a)

Gas molecules move randomly at high speed in all directions [1]

The molecules collide with the inner walls of the tyre [1]

Each collision exerts a force on the wall; the many collisions per second produce a steady pressure (force per unit area) on the tyre walls [1]

Mark 1: Molecules move randomly at high speed

Mark 2: Molecules collide with the walls

Mark 3: Collisions exert force / many collisions produce pressure

(b) 4 marks

A diver at the surface of a lake has 3.0 litres of air in her lungs at atmospheric pressure of 100 kPa. She dives to a depth where the total pressure on her body is 400 kPa. Assume the temperature remains constant.

(b) (i) 1 mark

Model Answer - Q2(b)(i)

For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume / pV = constant [1]

Mark 1: Pressure inversely proportional to volume at constant temperature

(b) (ii) 3 marks

Model Answer - Q2(b)(ii)

p₁V₁ = p₂V₂ [1]

100 x 3.0 = 400 x V₂ [1]

V₂ = 300 / 400 = 0.75 litres [1]

Mark 1: Correct formula p1V1 = p2V2

Mark 2: Correct substitution

Mark 3: Correct answer 0.75 litres

During summer in Bangalore, the temperature reaches 38 °C. During winter in Shimla, the temperature drops to -5 °C.

Model Answer - Q2(c)(i)

Bangalore: T = 38 + 273 = 311 K [1]

Shimla: T = -5 + 273 = 268 K [1]

Mark 1: 311 K (Bangalore)

Mark 2: 268 K (Shimla)

Model Answer - Q2(c)(ii)

Absolute zero is the lowest possible temperature, at which particles have minimum kinetic energy / stop moving (as far as possible) [1]

Absolute zero = -273 °C (or 0 K) [1]

Mark 1: Lowest possible temperature / minimum kinetic energy

Mark 2: -273 degrees C / 0 K

Question 3: Thermal Expansion and Specific Heat Capacity

Total: 12 marks

(a) 4 marks

Railway tracks in India are made of long steel rails. Gaps are deliberately left between adjacent rails.

(a) (i) 2 marks

Model Answer - Q3(a)(i)

When the temperature rises, the steel rails expand / increase in length [1]

Without gaps, the expanding rails would push against each other, causing the track to buckle / bend / deform, which is dangerous [1]

Mark 1: Rails expand when temperature rises

Mark 2: Without gaps, rails would buckle / deform (dangerous)

(a) (ii) 2 marks

Model Answer - Q3(a)(ii)

When heated, particles gain kinetic energy and vibrate with greater amplitude / vibrate more vigorously [1]

This pushes neighbouring particles slightly further apart, increasing the average separation between particles, causing the solid to expand [1]

Mark 1: Particles gain KE / vibrate more / greater amplitude

Mark 2: Average separation increases / particles pushed further apart

(b) 5 marks

A student uses an electric immersion heater rated at 48 W to heat 0.50 kg of cooking oil in an aluminium container. The mass of the aluminium container is 0.20 kg. The temperature rises from 22 °C to 52 °C in 5 minutes.

Specific heat capacity of aluminium = 900 J/(kg °C).

(b) (i) 2 marks

Model Answer - Q3(b)(i)

E = P x t = 48 x (5 x 60) = 48 x 300 [1]

E = 14 400 J [1]

Mark 1: Correct method E = Pt with time converted to seconds (300 s)

Mark 2: Correct answer 14 400 J

(b) (ii) 3 marks

Model Answer - Q3(b)(ii)

Energy absorbed by aluminium container: E_Al = mcΔθ = 0.20 x 900 x 30 = 5400 J [1]

Energy absorbed by oil: E_oil = 14 400 - 5400 = 9000 J [1]

c_oil = E / (mΔθ) = 9000 / (0.50 x 30) = 600 J/(kg °C) [1]

Mark 1: Correct energy absorbed by aluminium = 5400 J

Mark 2: Correct energy for oil = 14400 - 5400 = 9000 J

Mark 3: Correct SHC of oil = 600 J/(kg C)

A bimetallic strip is used in a simple fire alarm. It consists of two metals (brass and invar) bonded together. Brass expands more than invar for the same temperature rise.

Model Answer - Q3(c)(i)

The strip bends / curves with brass on the outside of the curve (since brass expands more) [1]

Mark 1: Strip bends / curves with brass on outside

Model Answer - Q3(c)(ii)

When the temperature rises (due to fire), the strip bends enough to touch / make contact with an electrical contact point [1]

This completes / closes the circuit, allowing current to flow through the alarm bell / buzzer, which sounds the alarm [1]

Mark 1: Strip bends to make contact / touch a contact

Mark 2: Completes circuit / alarm sounds

Question 4: Changes of State and Heating/Cooling Curves

Total: 11 marks

(a) 6 marks

The graph below shows the temperature of a pure substance as it is heated steadily from -20 °C. The substance starts as a solid.

(a) (i) 2 marks

Model Answer - Q4(a)(i)

Melting point = 40 °C (read from the flat section B) [1]

Boiling point = 80 °C (read from the flat section D) [1]

Mark 1: Melting point = 40 C

Mark 2: Boiling point = 80 C

(a) (ii) 2 marks

Model Answer - Q4(a)(ii)

The substance is melting / changing from solid to liquid during section B [1]

The energy supplied is being used to break the bonds / overcome the forces between particles, not to increase their kinetic energy, so the temperature does not rise [1]

Mark 1: Substance is melting / changing state

Mark 2: Energy breaks bonds / overcomes forces, not increasing KE

(a) (iii) 2 marks

Model Answer - Q4(a)(iii)

The substance is entirely liquid in section C [1]

In section B, the substance is a mixture of solid and liquid (both states coexist during melting) [1]

Mark 1: Section C is entirely liquid

Mark 2: Section B is a mixture of solid and liquid

(b) 3 marks

A cook in a kitchen notices that water left in an open pan slowly disappears over several hours, but when the pan is placed on a hot stove, the water bubbles vigorously and disappears quickly.

State three differences between evaporation and boiling.

Model Answer - Q4(b)

Evaporation occurs at any temperature below boiling point; boiling occurs only at the boiling point [1]

Evaporation occurs only at the surface of the liquid; boiling occurs throughout the liquid (bubbles form within the liquid) [1]

Evaporation is a slow, quiet process; boiling is rapid and vigorous (with visible bubbles) [1]

Mark 1: Temperature difference (any temp vs boiling point only)

Mark 2: Location (surface only vs throughout the liquid)

Mark 3: Rate / nature (slow vs rapid / bubbles)

After swimming in the sea, a person feels cold when they stand in a breeze. Explain, using the idea of particles, why evaporation causes cooling.

Model Answer - Q4(c)

The fastest / most energetic water molecules at the surface have enough energy to escape from the liquid [1]

This removes kinetic energy from the remaining liquid, so the average kinetic energy of the remaining molecules decreases, causing the temperature to fall / the skin feels cold [1]

Mark 1: Most energetic molecules escape from the surface

Mark 2: Average KE of remaining molecules decreases / temperature falls

Question 5: Conduction and Convection

Total: 12 marks

(a) 4 marks

A stainless steel spoon is placed in a cup of hot chai. After a short time, the handle of the spoon becomes hot.

(a) (i) 4 marks

Model Answer - Q5(a)(i)

Lattice vibration mechanism: Particles at the hot end gain kinetic energy and vibrate more vigorously [1]

These vibrating particles collide with neighbouring particles, transferring kinetic energy along the spoon from particle to particle [1]

Free electron mechanism: Metals have free / delocalised electrons that can move through the lattice [1]

Free electrons at the hot end gain kinetic energy, move rapidly through the metal, and transfer energy to particles further along by colliding with them. This is why metals are much better conductors than non-metals [1]

Mark 1: Hot particles vibrate more vigorously

Mark 2: Vibrations passed to neighbouring particles by collisions

Mark 3: Metals have free / delocalised electrons

Mark 4: Free electrons transfer energy rapidly through the metal

(b) 3 marks

A student wants to compare the thermal conductivity of copper and glass. She heats one end of a copper rod and one end of a glass rod of the same dimensions using identical Bunsen burners. Wax beads are attached at regular intervals along each rod.

(b) (i) 2 marks

Model Answer - Q5(b)(i)

The wax beads on the copper rod melt faster / fall off sooner than those on the glass rod [1]

More wax beads melt along the copper rod than along the glass rod (in the same time), showing copper conducts heat better / faster [1]

Mark 1: Wax beads on copper melt faster

Mark 2: More beads melt on copper / copper conducts better

(b) (ii) 1 mark

Model Answer - Q5(b)(ii)

Copper has free / delocalised electrons that transfer energy rapidly, whereas glass does not have free electrons and relies only on lattice vibrations (which is much slower) [1]

Mark 1: Copper has free electrons / glass does not

A room has a wall-mounted electric heater near the floor. The diagram below shows the heater on one side of the room.

Model Answer - Q5(c)(i)

Arrows showing warm air rising from the heater upward [1]

Arrows showing a complete circulation: across the ceiling, sinking on the far side (as it cools), and returning along the floor back toward the heater [1]

Mark 1: Warm air rising from heater

Mark 2: Complete convection loop shown with correct direction

Model Answer - Q5(c)(ii)

The heater warms the air near it. The warm air expands and becomes less dense than the surrounding cooler air [1]

The less dense warm air rises (and is replaced by cooler, denser air which moves in from the sides / below) [1]

This sets up a convection current / continuous circulation which distributes warm air throughout the room [1]

Mark 1: Warm air expands / becomes less dense

Mark 2: Less dense warm air rises / replaced by cooler denser air

Mark 3: Continuous circulation / convection current formed

Question 6: Radiation, Greenhouse Effect and Thermal Equilibrium

Total: 10 marks

(a) 3 marks

A student places two identical metal cans, one painted matt black and one painted shiny silver, each filled with the same volume of hot water at 80 °C. She records the temperature of the water in each can every 2 minutes for 20 minutes.

(a) (i) 2 marks

Model Answer - Q6(a)(i)

The matt black can will cool faster [1]

Because matt black surfaces are better emitters of infrared radiation than shiny silver surfaces, so the black can loses thermal energy more quickly [1]

Mark 1: Matt black can cools faster

Mark 2: Matt black is a better emitter of infrared radiation

(a) (ii) 1 mark

Model Answer - Q6(a)(ii)

Any one of: same volume/mass of water, same starting temperature, same type/material of can, same room temperature/surroundings, same size/shape of can, lids on both cans (to prevent convection/evaporation) [1]

Mark 1: Any valid controlled variable

(b) 5 marks

(b) (i) 3 marks

Model Answer - Q6(b)(i)

Short-wavelength radiation from the Sun passes through the atmosphere and warms the Earth's surface [1]

The warm Earth re-emits longer-wavelength infrared radiation [1]

Greenhouse gases (e.g. CO₂, methane, water vapour) in the atmosphere absorb some of this outgoing infrared radiation and re-radiate it back towards Earth, keeping it warmer than it would otherwise be [1]

Mark 1: Short-wavelength radiation from Sun passes through atmosphere / warms Earth

Mark 2: Earth re-emits longer-wavelength infrared radiation

Mark 3: Greenhouse gases absorb / re-radiate IR back towards Earth

(b) (ii) 2 marks

Model Answer - Q6(b)(ii)

The rate at which the Earth absorbs energy / radiation from the Sun is equal to the rate at which it emits / radiates energy into space [1]

Because energy in equals energy out, the average temperature of the Earth remains constant / stable [1]

Mark 1: Rate of energy absorbed = rate of energy emitted

Mark 2: Therefore average temperature remains constant

In many Indian cities, water storage tanks on rooftops are painted black. Explain why this is beneficial.

Model Answer - Q6(c)

Matt/dark black surfaces are good absorbers of infrared radiation [1]

The black tank absorbs more thermal energy / infrared radiation from the Sun, heating the water inside more effectively (useful for heating water for bathing without electricity) [1]

Mark 1: Black surfaces are good absorbers of infrared radiation

Mark 2: Absorbs more solar energy / heats water more effectively

Question 7: Combined Thermal Transfer and Applications

Total: 12 marks

(a) 4 marks

A vacuum flask (thermos flask) is designed to keep hot drinks hot or cold drinks cold for a long time. The diagram shows the main features of a vacuum flask.

Explain how each of the following features reduces thermal energy transfer:

(a) (i) 2 marks

Model Answer - Q7(a)(i)

The vacuum contains no particles / no matter [1]

So thermal energy cannot be transferred by conduction or convection (both require particles) [1]

Mark 1: Vacuum has no particles / no matter

Mark 2: Prevents conduction and convection

(a) (ii) 2 marks

Model Answer - Q7(a)(ii)

Shiny / silvered surfaces are poor emitters of infrared radiation, so the hot liquid emits less radiation outward [1]

Shiny / silvered surfaces are also good reflectors of infrared radiation, so any radiation is reflected back, reducing heat loss by radiation [1]

Mark 1: Shiny surfaces are poor emitters of infrared radiation

Mark 2: Shiny surfaces reflect infrared radiation back

(b) 4 marks

A blacksmith plunges a hot iron horseshoe of mass 0.80 kg at a temperature of 600 °C into a bucket containing 5.0 kg of water at 18 °C. The final temperature of the water and horseshoe is 28 °C.

Specific heat capacity of water = 4200 J/(kg °C).

(b) (i) 2 marks

Model Answer - Q7(b)(i)

E = mcΔθ = 5.0 x 4200 x (28 - 18) = 5.0 x 4200 x 10 [1]

E = 210 000 J (or 210 kJ) [1]

Mark 1: Correct substitution E = 5.0 x 4200 x 10

Mark 2: Correct answer 210 000 J

(b) (ii) 2 marks

Model Answer - Q7(b)(ii)

Energy lost by iron = energy gained by water = 210 000 J
c = E / (mΔθ) = 210 000 / (0.80 x (600 - 28)) = 210 000 / (0.80 x 572) [1]

c = 459 J/(kg °C) (accept 450-460 J/(kg °C)) [1]

Mark 1: Correct method: energy lost by iron = energy gained by water, correct temp change for iron (572 C)

Mark 2: Correct answer approximately 459 J/(kg C)

A pressure cooker used in Indian kitchens cooks food faster than an ordinary open pan. The pressure cooker has a sealed, heavy lid and a thick metal body.

Model Answer - Q7(c)(i)

Convection [1]

Mark 1: Convection

Model Answer - Q7(c)(ii)

The sealed lid traps steam / prevents steam from escaping [1]

This increases the pressure inside the cooker above atmospheric pressure [1]

At higher pressure, the boiling point of water increases (above 100 °C), so the food is cooked at a higher temperature, which speeds up the cooking process [1]

Mark 1: Sealed lid traps steam / prevents escape

Mark 2: Pressure inside increases above atmospheric

Mark 3: Boiling point of water increases / food cooks at higher temperature

Score Summary

Topic 2: Thermal Physics - Mock 2

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