particle model

Question 1

whats the error when a balance starts at a number greater than 0 and what can fix the problem

Answer 1

zero error

allow systematic error

1

(b)  reset the balance to zero g

Question 2

A student is reading the volume of water in the measuring cylinder.

Give two changes the student should make to increase the accuracy of the volume measurement.

Answer 2

place the measuring cylinder on a horizontal surface

1

view with eye in line with the level of the water

Question 3

(e)  Describe how the student could use a displacement method to determine an accurate value for the volume of a single coin.

Answer 3

add several coins to the measuring cylinder

allow a minimum of 5 coins if a number of coins is given

1

measure the change in the water level in the measuring cylinder

1

divide by the number of coins added

Question 4

(a)  Explain what happens to the internal energy of the coolant as its temperature increases.

Answer 4

(a)  the kinetic energy (and the potential energy) of the particles increases

allow the speed of the particles increases

1

so the internal energy increases because it is the sum of kinetic and potential energy (of the particles)

Question 4

(b)  What name is given to the energy needed to change the state of the liquid coolant?

Answer 4

specific latent heat of avporisation

Question 5

(c)  What happens to the mass of the coolant as it evaporates and becomes a vapour?

Answer 5

stays the same

Question 6

The compressor increases the density and temperature of the coolant vapour inside the pipe.

Explain why the pressure in the pipe increases.

Answer 6

more collisions per second

1

a greater force per collision

Question 7

The air in the building gains 400 J for every 100 J of energy transferred from the mains electricity supply to the compressor.

An advertisement claims that the heat pump system has an efficiency of 400%.

Explain why the advertisement is not correct.

Answer 7

the advertisement has ignored the energy input from the surrounding air

1

so the total energy input is greater than the energy supplied from the electricity

an answer that the total energy input comes from the electricity supply and the air outside the building gains the first two marking points

1

the efficiency must be less than 100%

Question 8

(c) Explain why the different thermal conductivities of metal and plastic are important in the design of the bowl.

Answer 8

metal: has a high thermal conductivity

1

which increases the rate of energy transfer from the mixture

allow ice cream for mixture

1

plastic: has a low thermal conductivity

1

which reduces the rate of energy transfer from the surroundings

Question 9

The heating element of the kettle was connected to the mains supply.

Explain why the temperature of the heating element increased.

Answer 9

electrons collide with particles in the heating element

allow there is a current in the heating element

1

which increases the (kinetic) energy of the particles (in the heating element)

(b)  the starting temperature of the water

should be controlled

Question 10

The temperature of the air inside the canister increases.

What happens to the movement of the air particles?

Answer 10

the (mean) speed of the particles would increase

Question 11

It could be dangerous if the temperature of the air inside the canister increased by a large amount.

Explain why

Answer 11

(if the temperature increases) the pressure increases

allow an explanation in terms of large pressure difference

1

so it could explode

Question 12

(f)  What happens to the volume of the air when it is released from the canister?

Answer 12

increases

Question 13

Energy is transferred to the water at a constant rate.

Explain why the graph is a different shape in parts A and B interal enrgy grapgh

Answer 13

in part A the increase in internal energy raises the temperature of the water

1

in part B the increase in internal energy changes the state

1

without changing the temperature

Question 14

When the water drops to a low level, the heater automatically switches off.

Explain what problem would be caused if the heater did not automatically switch off.

Answer 14

(c) the heater would continue to transfer energy which would not be transferred to the water

1

so would raise the temperature of the device

1

causing it to be damaged

Question 15

(e) Which statement gives the purpose of the earth wire?

Answer 15

stops casing becoming lie

Question 16

(b) Explain why heating a gas increases the average speed of the gas particles.

Answer 16

heating increases the temperature of the gas

1

temperature is proportional to kinetic energy

1

if kinetic energy increases speed increases

Question 17

Water can exist as either a liquid or a gas at 100 °C.

Explain why a mass of gaseous water at 100 °C contains more energy than an equal mass of liquid water at 100 °C.

Answer 17

energy is needed to change the state of the water

1

to break the bonds

Question 18

Central heating boilers burn gas and use the energy released to heat water.

Modern condensing central heating boilers take advantage of the energy that is released when water condenses.

Waste water vapour produced when the water is heated in the boiler is used to preheat the cold water entering the boiler.

Give some of the arguments in favour of condensing boilers compared to older non-condensing boilers

Answer 18

because the water is preheated) the change in temperature of the water
is less

• so less energy is used to heat the water (E=mcΔθ)
• therefore they (condensing boilers) are more efficient
• so less energy is wasted
• less gas is burned to heat the same amount of water
• less waste gas (CO2) is produced by the boiler or (because less gas
  is used) they are cheaper to run / save money

Question 19

A student investigated the cooling effect of evaporation.

She used the equipment in Figure 1 to measure how the temperature of three different liquids changed as the liquids evaporated.

Answer 19

surface area

or

duration of experiment

Question 20

(b) Give two advantages of using dataloggers and temperature probes compared to using the thermometer shown in Figure 2.

Answer 20

takes readings automatically

ignore easier or takes readings for you

• takes readings more frequently
• reduces / no instrument reading error

ignore human error

• higher resolution

allow better resolution

• don’t need to remove probe to take reading
• more accurate

Question 21

(d) Explain how the evaporation of a liquid causes the temperature of the remaining liquid to decrease.

Answer 21

particles with more energy

accept particles with higher speeds

1

leave the (surface of the) liquid

1

(which) reduces the average (kinetic) energy (of the remaining particles

Question 22

(i) The temperature of the water falls at the fastest rate just after the heater switches off.

Answer 22

there is a bigger temperature difference between the water and the surrounding air

accept the water is hottest / hotter

1

so the transfer of energy (from hot water) is faster