IGCSE Physics 0625 — Topic 2: Thermal Physics

Question 1

Which statement correctly describes the arrangement of particles in a solid?

AParticles are far apart and move randomly at high speed BParticles are closely packed in a regular pattern and vibrate about fixed positions CParticles are close together but can slide past each other freely DParticles are widely spaced and move in straight lines

Question 2

A student observes smoke particles in a glass cell using a microscope. The smoke particles move in random, jerky paths. What causes this motion?

AConvection currents in the air BElectrical charges on the smoke particles CCollisions between invisible air molecules and the visible smoke particles DGravity pulling the smoke particles downward

Question 3

A sealed syringe contains gas. The piston is pushed inward slowly at constant temperature. What happens to the gas pressure?

AIt decreases because particles slow down BIt stays the same because temperature is unchanged CIt increases because particles become larger DIt increases because particles hit the walls more frequently

Question 4

Which row correctly describes the properties of the three states of matter?

ASolid: fixed shape, fixed volume | Liquid: fixed shape, fixed volume | Gas: no fixed shape, no fixed volume BSolid: no fixed shape, fixed volume | Liquid: fixed shape, no fixed volume | Gas: no fixed shape, no fixed volume CSolid: fixed shape, no fixed volume | Liquid: no fixed shape, fixed volume | Gas: no fixed shape, no fixed volume DSolid: fixed shape, fixed volume | Liquid: no fixed shape, fixed volume | Gas: no fixed shape, no fixed volume

Question 5

A balloon is left in the sun in Bangalore on a hot day. It expands. Using the kinetic particle model, which explanation is correct?

AThe gas particles get larger when heated BThe gas particles move faster, collide with the walls harder and more often, pushing the walls outward CThe number of gas particles increases DThe atmospheric pressure outside increases

Question 6

Which process involves a change from liquid to gas at a temperature below the boiling point?

ABoiling BCondensation CEvaporation DMelting

Question 7

A sealed aerosol can has a warning: “Do not expose to temperatures above 50 °C.” Using the kinetic model, what is the risk?

AThe liquid will freeze BThe metal can will melt CThe particles will become smaller DGas pressure increases as particles move faster, and the can could burst

Question 8

In Brownian motion experiments, which particles are directly observed under the microscope?

AIndividual gas molecules BAtoms of the gas CLarger visible particles such as smoke or pollen DElectrons moving between atoms

Question 9

Gas molecules in a container exert pressure on the walls. Which statement about this pressure is correct?

APressure is caused by gas molecules sticking to the walls BPressure is caused by gas molecules colliding with the walls and exerting a force CPressure is caused only by the weight of the gas DPressure decreases when more gas molecules are added at constant volume and temperature

Question 10

When a liquid evaporates, the remaining liquid cools down. Which explanation is correct?

AThe slowest particles escape first, leaving faster particles behind BEnergy is transferred from the surroundings into the liquid CThe fastest particles escape from the surface, reducing the average kinetic energy of those remaining DThe volume of liquid increases, spreading the energy over more particles

Question 11

A drop of ink is placed in a beaker of hot water and in a beaker of cold water. The ink spreads faster in hot water because:

AHot water has fewer particles BParticles in hot water move faster, so diffusion happens more quickly CThe ink is lighter in hot water DCold water is more dense and blocks the ink

Question 12

Which statement about particles in a gas is correct?

AAll gas particles move at the same speed BGas particles move in curved paths between collisions CGas particles are in constant random motion and travel in straight lines between collisions DGas particles attract each other strongly

Question 13

What is the value of absolute zero on the Celsius scale?

A0 °C B−100 °C C−273 °C D−373 °C

Question 14

A gas is at a temperature of 27 °C. What is this temperature in kelvin?

A27 K B246 K C300 K D373 K

Question 15

At absolute zero, what happens to the particles of a substance?

AThey have minimum kinetic energy and virtually stop moving BThey move at maximum speed CThey expand to fill any container DThey gain electrical energy

Question 16

A fixed mass of gas at constant temperature has a volume of 600 cm³ at a pressure of 100 kPa. The volume is reduced to 200 cm³. What is the new pressure?

A33 kPa B100 kPa C200 kPa D300 kPa

Question 17

Which graph correctly shows the relationship between pressure and volume for a fixed mass of gas at constant temperature (Boyle’s Law)?

AA straight line through the origin with positive gradient BA straight line through the origin with negative gradient CA curve that decreases — as volume increases, pressure decreases DA horizontal straight line

Question 18

Convert 350 K to degrees Celsius.

A350 °C B623 °C C77 °C D−77 °C

Question 19

A gas has pressure 200 kPa and volume 50 cm³. The pressure is changed to 100 kPa at constant temperature. What is the new volume?

A25 cm³ B50 cm³ C100 cm³ D200 cm³

Question 20

Why does a bicycle tyre feel warm after being pumped up quickly?

AFriction between the pump handle and barrel BWork is done compressing the gas, increasing the kinetic energy of gas particles CThe metal valve conducts heat from the ground DThe rubber expands and releases stored energy

Question 21

A steel bridge has expansion joints. What is their purpose?

ATo make the bridge look attractive BTo allow the bridge to expand and contract with temperature changes without cracking CTo reduce the weight of the bridge DTo allow water to drain through

Question 22

A bimetallic strip is made of brass and iron bonded together. When heated, the strip curves. This happens because:

ABrass and iron have different specific heat capacities BBrass expands more than iron, so the strip bends with brass on the outside CIron melts at a lower temperature than brass DThe glue between them expands

Question 23

Which substance expands the most for a given temperature rise?

ASolid BLiquid CGas DThey all expand equally

Question 24

A metal ball just passes through a metal ring at room temperature. After heating the ball, it no longer passes through. This demonstrates:

AThe ball has gained mass BThermal expansion of the solid metal ball CThe ring has contracted DThe ball has changed shape permanently

Question 25

2.0 kg of water (specific heat capacity 4200 J/(kg °C)) is heated from 20 °C to 70 °C. How much energy is needed?

A42 000 J B168 000 J C420 000 J D588 000 J

Question 26

A 0.5 kg block of aluminium (specific heat capacity 900 J/(kg °C)) is supplied with 9000 J of energy. What is its temperature rise?

A5 °C B10 °C C20 °C D40 °C

Question 27

Sand on a beach gets much hotter than the sea on a sunny day. This is because:

ASand is darker than water BWater reflects all sunlight CSand has a lower specific heat capacity than water, so it heats up more for the same energy input DThe sea is deeper than the sand

Question 28

An electric heater supplies 12 000 J of energy to 0.5 kg of a liquid. The temperature rises from 20 °C to 80 °C. What is the specific heat capacity of the liquid?

A200 J/(kg °C) B400 J/(kg °C) C800 J/(kg °C) D2400 J/(kg °C)

Question 29

A substance is heated at a constant rate. The temperature-time graph shows a flat section at 80 °C. What is happening during this flat section?

AThe substance is cooling down BThe heater has been turned off CThe substance is changing state — energy is being used to break bonds between particles, not to raise temperature DThe thermometer is broken

Question 30

Which statement correctly describes a difference between boiling and evaporation?

ABoiling occurs at any temperature; evaporation occurs only at the boiling point BBoiling occurs throughout the liquid at a fixed temperature; evaporation occurs only at the surface at any temperature CBoiling is slower than evaporation DEvaporation requires more energy than boiling

Question 31

Which of the following would increase the rate of evaporation of water from a bowl?

ACovering the bowl with a lid BIncreasing the humidity of the surrounding air CDecreasing the temperature of the water DIncreasing the surface area of the water and blowing air across it

Question 32

During melting, the temperature of a pure substance stays constant because:

ANo energy is being supplied BEnergy is being used to overcome forces between particles rather than increasing kinetic energy CThe substance is losing energy to the surroundings DThe thermometer cannot measure temperatures during melting

Question 33

A pressure cooker is used to cook rice faster in a Bangalore kitchen. It works because:

AThe sealed container prevents steam from escaping, increasing pressure, which raises the boiling point of water BThe metal container conducts heat better than a regular pot CThe pressure reduces the boiling point so water boils faster DThe rubber seal insulates the pot

Question 34

A metal spoon left in a cup of hot chai becomes hot at the handle end. Which method of heat transfer is mainly responsible?

AConvection BRadiation CConduction DEvaporation

Question 35

Metals are good conductors of heat because:

AThey are shiny and reflect heat BThey contain free electrons that can transfer kinetic energy quickly through the material CThey are heavy DThey have low specific heat capacity

Question 36

A room heater is placed on the floor. Warm air rises and cool air moves in to replace it. This creates a convection current. Which statement explains why warm air rises?

AWarm air is lighter because it contains fewer molecules BWarm air expands, becomes less dense than the surrounding cooler air, and floats upward CWarm air is pushed up by the heater fan DGravity has less effect on warm air

Question 37

Which surface is the best absorber of infrared radiation?

AShiny white surface BShiny silver surface CDull black surface DPolished metal surface

Question 38

A vacuum flask keeps hot drinks hot and cold drinks cold. Which feature reduces heat loss by conduction and convection?

AThe shiny silvered walls BThe vacuum between the double walls CThe plastic cap DThe outer casing

Question 39

The Earth receives energy from the Sun by:

AConduction through the atmosphere BConvection through space CRadiation, which can travel through the vacuum of space DConduction through the vacuum of space

Question 40

A car engine has a radiator with thin metal fins. Cool air flows over the fins when the car moves. This system cools the engine by:

AConduction only BRadiation only CConduction from the coolant to the fins, and then convection as air flows over the fins DEvaporation of the coolant

Paper 2 — Multiple Choice

Section A: Kinetic Particle Model (2.1)

Section B: Temperature and Gas Laws (2.1 – 2.2)

Section C: Thermal Expansion and Specific Heat Capacity (2.2)

Section D: Changes of State (2.2)

Section E: Transfer of Thermal Energy (2.3)