Past papers- 2. thermal physics

Question 1

State and explain the two ways that thermal energy is conducted in a metal

Answer 1

delocalised / free / mobile electrons
electrons move through metal OR electrons collide with distant particles OR electrons carry energy through the metal

lattice vibrations transfer energy to neighbouring particles OR particles vibrate and cause nearby / adjacent particles to
vibrate OR vibrating particles collide with particles transferring energy (molecules gain KE OR vibrate more)

Question 2

Explain, in terms of forces and distances between particles, why the gas occupies a much greater volume than it does as a liquid.

Answer 2

(attractive) forces (between particles are much) greater in liquids (than in gases)

particles in gases are (much) further apart (than in liquids)

Question 3

ways in which boiling differs from evaporation.

Answer 3

occurs at a fixed temperature
takes place throughout the liquid

Question 4

When the heaters are first switched on, the temperature of the air immediately below the ceiling increases more quickly than the temperature of the air in the rest of the room. Explain why this happens.

Explain, in terms of the particles of helium, how the pressure of the helium remains constant after temperature and volume was increased.

Answer 4

1. heated / hot(ter) / warm(er) air is less dense OR cool(er) air is more dense

heated / hot(ter) / warm(er) air rises (to ceiling displacing cooler air) OR cool(er) air falls (displaced by warm(er) air)

2. (higher temperature means) particles collide (with rubber) harder / with more force / with greater momentum (change)

(larger volume means) particles collide (with rubber) less frequently OR (larger volume means) larger (surface) area (for particle collisions)

effect of larger volume cancels effect of increased temperature OR the effect of larger area cancels the effect of larger force OR P = F / A so the two changes cancel each other

Question 5

The efficiency of the lamp is less than the value determined.
Suggest one reason for this

Answer 5

temperature change is an underestimate (due to thermal energy losses)

(thermal energy is) transferred from the water (to air / beaker / bench)

energy (other than light) transferred in lamp (filament / glass / internal structure)

(some) water evaporates

Question 6

Explain what is meant by the term absolute zero. Refer to particles in your answer.

Answer 6

(temperature at which) particles have least
EK / kinetic energy

lowest possible temperature

Question 7

why the time calculated is the minimum time needed to
increase the temperature of the air in the room

State the main methods of thermal energy transfer from the room to outside which are reduced by this type of window.

Answer 7

a. (thermal) energy is transferred to furniture / walls / objects (in the room)

(thermal) energy is transferred through windows / doors / floor / ceiling / from the room

(2019-Thermal energy used to raise temperature of air entering room via draughts / openings )

b. conduction AND convection

Question 8

Describe, in terms of the motion and arrangement of particles, the structures of solids and gases.

Answer 8

(solids) particles vibrate
(gases) particles move freely
(gas) particles move quickly ((with high speed
freely, zig-zag, in straight lines in all directions)

(solids) particles in fixed / close positions
(gases) particles randomly arranged (in container) / wide separation

Question 9

Define specific heat capacity

Answer 9

(specific heat capacity is the) energy required to raise 1 kg / unit mass by 1 °C / 1 K / 1 kelvin / unit temperature

Question 10

Describe the process by which the volume of water in the puddle decreases.

Explain, in terms of molecules, how sweating helps to cool your body on a hot day.

Answer 10

• (Amount of water in the pool decreases) as water evaporates / becomes water vapour / gas
• The (more) energetic molecules escape OR fast(er) molecules escape OR molecules with more (kinetic) energy escape
• From the surface of the water
• (thermal) energy in the skin / body transferred to (molecules of) sweat
• These molecules (have enough KE to) escape from the skin / become water vapour
• Leaving behind molecules with lower average speed / average kinetic energy so temp dec
• Which leaves the skin / body at a lower temperature- temperature related to speed / energy of molecules

Question 11

The heating element in Fig. 4.1 remains switched on. The temperature of the sand remains constant at a value above room temperature.

Explain why the temperature of the sand remains constant.

Answer 11

(sand is warmer than surroundings and so thermal) energy (constantly) is lost from the sand

(at a constant temperature) rate of (thermal) energy supplied to the sand is equal to rate of (thermal) energy lost from sand

Question 12

Describe how energy from the Sun reaches the Earth and warms the road.

Answer 12

any three from:

radiation
light / infrared / electromagnetic (radiation)
travel through space / vacuum
absorbed by road

Question 13

A cyclist travelling along the road notices that a cool breeze is blowing from the sea to
the land.

Explain how convection produces this breeze. You may include a diagram if it helps your
answer.

Answer 13

density (of air above road) decreases or density (of hot air) decreases

air (above land / road) rises or air (that is hot) rises

air (above road) replaced by cool air / air from above sea

Question 14

Explain, in terms of forces and the motion of air molecules, the cause of the motion of the smoke particles.

Answer 14

 air molecules bombard smoke particles
 air molecules are small (compared to smoke particles) / have small(er) mass
 air molecules are very fast moving
 air molecules move in random directions
 (collisions exert unbalanced) forces on smoke particles

((Change direction at each collision OR undergo Brownian motion))

Question 15

Describe an experiment to show whether a black surface or a white surface is the better emitter of radiation. You may draw a diagram.

State two quantities in the experiment that you described that must be identical during the test.

Answer 15

1. equipment- e.g. black container, white container, thermometers or Leslie’s cube and detector

warm / hot water in container and temperature decreases recorded or time to reach a given temperature / to cool
or warm / hot water in cube and meter readings recorded

better emitter surface cools quicker or greater reading from better emitter surface

2. initial temperature of water
   mass / volume of water
   dimensions / surface area of container
   time of cooling
   mass of container
   shape of container
   smoothness of surface

surface area of face (of cube)
distance of detector
temperature of water at time
of measurement
smoothness of surface

Question 16

Explain why the red light does not change direction as it enters the plastic block. ( entering from curve of a protractor)

Answer 16

angle of incidence is 0°
(hence) angle of refraction is 0°
or
all the wavefront hits the plastic at the same time
all slows down at the same time

Question 17

The power station uses some of its waste thermal energy to heat water for houses in a nearby town.

State one problem of using waste energy in this way if the power station is far from the town.
Suggest a way of reducing this problem.

Answer 17

water will cool (too much) / thermal energy lost (during transfer)
lag/insulate (pipes) OR transport in a poor conductor of thermal energy

Question 18

State, in terms of molecules, what is meant by an increase in internal energy.

Answer 18

increase in kinetic energy of molecules or increase in potential energy of molecules

Question 19

Explain, in terms of molecules, why a liquid expands when heated.
Explain, in terms of molecules, why a liquid expands more than a solid when heated.

Answer 19

molecules / they speed up or gain kinetic energy
molecules move further apart or push others away

forces between liquid molecules weak(er than in solids)
less energy / work done to separate molecules or greater separation for same work done / same increase in energy

Question 20

State one everyday problem that is a result of thermal expansion.

Suggest and explain one way of solving this problem.

Answer 20

bridges buckle (in hot weather)

allow gaps at the ends of the bridge
as the bridge expands the gaps close

Question 21

Explain how using the holder makes it more comfortable to hold the plastic cup.

Suggest and explain another action that reduces the rate of cooling more effectively.

Answer 21

air good insulator / poor conductor

holder / it stops / reduces conduction OR no / less thermal energy conducted (to hand)

temperature (of outside of holder) lower (than cup) OR less energy to skin / hand / person

5(b) (put a) lid / cover (on cup) B1
less / no convection (from surface) B1
less / no evaporation (from surface / container)

Question 22

A cup of water contains 250cm3 of water at a temperature of 0°C. An identical cup contains 250cm3 of a mixture of ice and water at a temperature of 0°C.
The temperature of the surrounding air is 20°C.
State and explain which cup contains the liquid with the lower temperature after 10 minutes.

Answer 22

cup containing mixture of ice and water M1
mixture of ice and water will remain at 0 °C until all ice is melted (but temperature of water at 0 °C rises)
or reverse argument
OR energy needed for change of state so temperature doesn’t rise until this has taken place

Question 23

Describe simple experiments to mark the positions of the fixed points on this liquid-in-glass thermometer.

State the property of the liquid which ensures that the scale on a liquid-in-glass thermometer
is linear.

Answer 23

(place) in melting ice
when bead has stopped moving OR owtte mark as lower fixed point / 0 °C

(place) in steam (above boiling water)
when bead has stopped moving OR owtte mark as upper fixed point / 100 °C

expands uniformly (with temperature) OR same distance between all degree intervals

Question 23

On a sunny day, the temperature of the sand on a beach is much higher than the temperature of the sea.

Answer 23

(specific) heat capacity of water is much higher than (specific) heat capacity of sand
same rate of energy supplied to sand and sea

Question 24

Describe how the molecular structure of the liquid metal differs from that of the solid metal

Answer 24

(molecules /they) have an irregular arrangement / not ordered/random arrangement

(molecules /they) are (slightly) further apart (on average)

(molecules /they are) not fixed in place

Question 24

Solids have a fixed shape. Liquids adapt to the shape of their container. Gases fill their container. Explain in terms of forces between molecules and arrangement of molecules, why solids, liquids and gases have these properties.

Answer 24

Solids – molecules in lattice arrangement
solids – strong forces between molecules

liquids – molecules not fixed in place OR molecules have an irregular arrangement OR molecules (slightly) further apart (on average) than in solids OR spaces between the molecules
liquids – (average) forces too weak to keep molecules in a definite pattern OR forces just enough to hold molecules in the bulk of the liquid

gases – molecules far apart
gases – weak / no forces between molecules (except during collisions)

Question 24

Describe, in terms of molecules, why the temperature of the whole of the plastic spoon increases.

The plastic spoon is replaced by a metal spoon. Describe an additional process by which the temperature of the whole of this spoon increases

Answer 24

Molecules of hot liquid collide with (surface of) spoon.
transfer energy / heat to (molecules of) spoon.
(amplitude of) vibration of spoon’s molecules increases / is faster (increasing spoon’s temperature)

Molecules of hot liquid (also) transfer energy to (free) electrons in the spoon.
These (free) electrons move through the metal.

Question 24

A student wants to investigate good and bad absorbers of thermal radiation. She has the apparatus
shown in Fig. 5.1, a supply of cold water and a metre rule.

small polished can
small black-painted can
2 thermometers
electric heater

Explain how the student could use the apparatus she has available to carry out her investigation.

Describe the results she would expect to obtain. Draw a diagram of the set-up.

Answer 24

diagram shows cans placed near heater

put thermometers in water AND observe readings

good detail e.g.
cans equal distances from heater
same water volumes/levels
thermometers same positions in cans

higher thermometer reading in black (painted) can OR black (surface) good/best/better absorber

Question 25

The piston in the cylinder is free to move. The piston moves to the left when the temperature of the gas is decreased.

Explain, in terms of the molecules of the gas, why this happens

Answer 25

(average) speed of the molecules decreases

molecules collide less often (on the piston and the walls of the cylinder)

smaller momentum change molecules (on collision)

piston now has a greater force on its right-hand side OR pressure less than atmospheric

Question 26

The temperature of the surrounding air increases to a temperature above 23 °C.

(i) Suggest one reason why there is a delay before the temperature of the water increases to 23 °C

Answer 26

Glass is a poor conductor of heat OR glass conducts heat at a slow rate

OR water has a high (specific) heat capacity