Web viewEach word may be used once or ... The heat exchanger uses heat from the air outside to warm the inside ... Heat exchangers are devices used to transfer heat from

P1 03 Energy Transfer by Heating

269 minutes

269 marks

Q1. A student was asked to investigate the heat loss from two metal cans, L and M. The cans were identical except for the outside colour.

The student filled the two cans with equal volumes of hot water. He then placed the temperature sensors in the water and started the data logger. The computer used the data to draw the graph below.

(a) Which one of the following is a categoric variable?

Put a tick ( ) in the box next to your answer.

the outside colour of the cans

the starting temperature of the hot water

the time

the volume of hot water (1)

(b) For can L, state the temperature drop of the water:

(i) in the first two-minute interval

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(ii) in the second two-minute interval.

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(c) In both cans the water cooled faster at the start of the investigation than at the end of the investigation. Why?

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(d) One can was black on the outside and the other can was white on the outside.

What colour was can L? ..............................................

Explain the reason for your answer.

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(Total 7 marks)

Q2. (a) The graph shows the temperature inside a flat between 5 pm and 9 pm. The central heating was on at 5 pm.

(i) What time did the central heating switch off?

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(ii) Closing the curtains reduces heat loss from the flat.

What time do you think the curtains were closed?

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Give a reason for your answer.

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(b) Less heat is lost through double-glazed windows than through single-glazed windows.

Complete the following sentences by choosing the correct words from the box. Each word may be used once or not at all.

conduction conductor convection evaporation insulator radiation

Air is a good ........................................... . When trapped between two sheets of glass it

reduces heat loss by .......................................... and ....................................................(3)

(c) The table gives information about three types of house insulation.

Type of insulation Cost toinstall

Money save eachyear on heating

Payback time

bills

Double glazing £4000 £200 20 years

Loft insulation £300 £100 3 years

Cavity wall insulation

£600 £150

(i) Use the information in the table to calculate the payback time for cavity wall insulation.

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(ii) Explain why people often install loft insulation before installing double glazing or cavity wall insulation.

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(Total 9 marks)

Q3. A student had read about a glacier that had been covered in insulating material. The idea was to slow down the rate at which the glacier melts in the summer.

She investigated this idea using the apparatus shown in the diagram.

(a) These are the steps taken by the student.

• Measure 30 cm3 of cold water into a boiling tube.

• Place the boiling tube 25 cm from an infra red lamp.

• Record the temperature of the water.

• Switch on the infra red lamp.

• Record the temperature of the water every minute for 5 minutes.

• Repeat with boiling tubes covered in different insulating materials.

(i) Why did she use an infra red lamp?

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(ii) Name one control variable in this investigation.

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(iii) Give one advantage of using a temperature sensor and data logger instead of a glass thermometer to measure temperature.

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(b) The results of the investigation are shown in the graph.

(i) Why did the student use a boiling tube with no insulation?

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(ii) From her results, what should she recommend is used to insulate the glacier?

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(iii) Explain why the insulation recommended by the student will reduce the heat transfer from the Sun to the glacier.

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(c) Explain, in terms of particles, how heat is transferred through the glass wall of a boiling tube.

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(Total 9 marks)

Q4. The diagram shows potatoes being baked in a gas oven. Each potato has a metal skewer pushed through it.

(a) Explain how heat is transferred by the process of convection from the gas flame at the bottom of the oven to the potatoes at the top of the oven.

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(b) The metal skewers help the potatoes to cook by transferring heat to the inside of the potatoes.

By what method is heat transferred through a metal skewer?

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(c) When the potatoes are taken from the oven, they start to cool down.

Suggest one factor that will affect how fast a potato cools down.

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(d) If the potatoes need to be kept hot, they may be wrapped in shiny aluminium foil.

Why does this help to keep the potatoes hot?

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(Total 6 marks)

Q5. (a) In winter, energy is transferred from the warm air inside a house to the air outside.

(i) What effect will the energy transferred from the house have on the air outside?

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(ii) What would happen to the energy transfer if the temperature inside the house were reduced? Assume the temperature outside the house does not change.

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(b) To increase energy efficiency, a householder installs a heat exchanger to an outside wall of the house. The heat exchanger uses heat from the air outside to warm the inside of the house. The diagram shows the idea of the heat exchanger.

Physics Through Applications edited by J Jardine et el (OUP, 1989), copyright ©Oxford University Press, reprinted by permission of Oxford University Press.

(i) Why does the heat exchanger cost money to run?

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(ii) The heat exchanger is cost effective in reducing energy consumption.Explain why.

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(Total 5 marks)

Q6. The diagram shows a fridge-freezer.

(a) By which method is heat transferred through the walls of the fridge-freezer?

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(b) The inside of the fridge is at 4 °C. The inside of the freezer is at –18 °C.

Into which part of the fridge-freezer will the rate of heat transfer be greater?

Draw a ring around your answer.

the fridge the freezer


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(c) The outside surface of the fridge-freezer is white and shiny.

Give two reasons why this type of surface is suitable for a fridge-freezer.

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2 ..................................................................................................................................

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(2)(Total 4 marks)

Q7. (a) The graph compares how quickly hot water cooled down in two glass beakers withdifferent surface areas.

The volume of water in each beaker was the same.

Describe how the surface area of the water affected how fast the water cooled down.

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(b) Some foxes live in a hot desert environment.

This type of fox has very large ears.

Explain how the size of the fox’s ears help it to keep cool in a hot desert.

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(2)

(c) Polar bears and reindeer are adapted to live in cold environments.

Use the words in the box to complete the following sentences.

conduction convection radiation

(i) The white colour of a polar bear’s fur helps to keep the polar bear warm by

reducing the heat lost by .................................................. .(1)

(ii) The hairs of a reindeer are hollow. The air trapped inside the hairs reduces the

heat lost by .................................................. .(1)

(Total 5 marks)

Q8. A vacuum flask is designed to reduce the rate of heat transfer.

(a) (i) Complete the table to show which methods of heat transfer are reduced by each of

the features labelled in the diagram.

The first row has been done for you.

Feature Conduction Convection Radiation

vacuum

silvered surfaces

plastic cap

(2)

(ii) Explain why the vacuum between the glass walls of the flask reduces heat transfer by conduction and convection.

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(b) The diagram shows a gas flame patio heater.

(i) Explain why the top surface of the reflecting hood should be a light, shiny surface rather than a dark, matt surface.

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(ii) Most of the chemical energy in the gas is transformed into heat. A small amount of chemical energy is transformed into light.

Draw and label a Sankey diagram for the patio heater.

(2)

(iii) State why the total energy supplied to the patio heater must always equal the total energy transferred by the patio heater.

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(Total 9 marks)

Q9.The diagram shows the apparatus used by a student to investigate the cooling effect produced by evaporation.

After wetting the paper with water, the student took a temperature reading every 30 seconds.

The student’s results are given in the table.

Time in seconds 0 30 60 90 120 150

Temperature in °C 21.0 16.0 12.5 11.5 12.5 10.5

(a) (i) One of the student’s results is anomalous.

Draw a ring around the anomalous result in the table.

Suggest one reason why the anomalous result may have occurred.

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(ii) What should the student have done to improve the validity of her data?

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(iii) Explain the advantage in this investigation of using a temperature sensor and a data logger rather than a thermometer and a stop clock.

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(b) The graph shows that the molecules in a liquid do not all have the same speed.

Use the information in the graph to explain why a liquid cools down when it evaporates.

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(c) Evaporation helps to regulate body temperature. The evaporation of sweat from the body transfers energy, producing a cooling effect.

State and explain the effect of an increase in humidity on the cooling effect produced by the evaporation of sweat.

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(Total 13 marks)

Q10. The picture shows one type of solar water heater. Water from the tank is slowly pumped through copper pipes inside the solar panel where the water is heated by energy from the Sun.

(a) Explain why the copper pipes inside the solar panel are painted black.

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(b) Each day the average European family uses 100 kg of hot water.To kill bacteria, the water going into the tank at 20 °C must be heated to 60 °C.

Calculate the energy needed to increase the temperature of 100 kg of water by 40 °C.

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

Write down the equation you use, and then show clearly how you work out your answer.

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Energy transferred = .................................... J(2)

(c) The bar chart shows how the amount of solar energy transferred to the water heater varies throughout the year.

How many months each year will there not be enough solar energy to provide the hot

water used by an average European family?

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(d) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.

The water in the tank could be heated by using an electric immersion heater.

Outline the advantages and disadvantages of using solar energy to heat the water rather than using an electric immersion heater.

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(Total 11 marks)

Q11. The bar charts show the rate of energy loss from the body of a runner at the start of a marathon race and half way through the race.

(a) It is important that the energy loss by evaporation increases during the race.

Explain why.

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(b) At the end of the marathon the runner covers herself in a silvered space blanket.

Explain how the space blanket helps keep the runner warm.

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(Total 4 marks)

Q12. (a) The diagram shows two switches on a room heater. The heater has three power settings. The power produced by two of the settings is given in the table.

Setting Power in watts

Low 700

Medium 1400

High

(i) When both switches are on, the heater works at the high power setting.

What is the power of the heater, in kilowatts, when it is switched to the high power setting?

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Power = ......................................................... kilowatts(1)

(ii) The heater is used on the high power setting. It is switched on for 1½ hours.

Use the equation in the box to work out the energy transferred from the mains to the heater in 1½ hours.

energy transferred = power × time

Show clearly how you work out your answer and give the unit.

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Energy transferred = ....................................................(3)

(iii) This type of heater is a very efficient device.

What is meant by a device being very efficient?

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(b) The graph shows how the temperature of a room changes during the 1½ hours that the heater is used.

After 1 hour, the temperature of the room has become constant, even though the heater is still switched on.

Explain why.

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(Total 7 marks)

Q13. Heat exchangers are devices that are used to transfer heat from one place to another.

The diagram shows a simple heat exchanger used by a student in an investigation.Heat is transferred from the hot water inside the pipe to the cold water outside the pipe.

(a) By which process is heat transferred from the hot water inside the pipe to the cold water outside the pipe?

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(b) The student wanted to find out if the efficiency of a heat exchanger depends on the material used to make the pipe. The student tested three different materials. For each material, the rate of flow of hot water through the pipe was kept the same.

The results obtained by the student are recorded in the table and displayed in the bar chart.

Material

Temperature of the cold waterat the start in °C

Temperature of the cold waterafter 10 minutes in °C

Copper 20 36

Glass 20 23

Plastic 20 21

(i) The rate of flow of hot water through the pipe was one of the control variables in the investigation.

Give one other control variable in the investigation.

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(ii) Why did the student draw a bar chart rather than a line graph?

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(iii) Which one of the three materials made the best heat exchanger?

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(c) The student finds a picture of a heat exchanger used in an industrial laundry.The heat exchanger uses hot, dirty water to warm cold, clean water.

Why does this heat exchanger transfer heat faster than the heat exchanger used by the student in the investigation?

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(Total 6 marks)

Q14. (a) The diagram shows a ski jacket that has been designed to keep a skier warm.The jacket is made from layers of different materials.

(i) The inner layer is shiny to reduce heat transfer.

Which process of heat transfer will it reduce?

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(ii) Why is the layer of fleece good at reducing the transfer of heat from a skier’s body?

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(b) A student tested four different types of fleece, J, K, L and M, to find which would make the warmest jacket. Each type of fleece was wrapped around a can which was then filled with hot water.The temperature of the water was taken every two minutes for 20 minutes.

The graph shows the student’s results.

(i) In each test, the water cooled faster during the first five minutes than during the last five minutes. Why?

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(ii) To be able to compare the results, it was important to use the same volume of water in each test.

Give one other quantity that was the same in each test.

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(iii) Look at the graph line for fleece K.

Estimate what the temperature of the water in the can wrapped in fleece K would be after 40 minutes.

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(iv) Which type of fleece, J, K, L or M, should the student recommend to be used in the ski jacket?

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(Total 7 marks)

Q15.The diagram shows how the metal chimney from a log-burning stove passes through the inside of a house.

(a) Explain how heat is transferred by the process of convection from the inside of the stove to the top of the chimney.

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(b) Although the outside of the chimney becomes very hot, there is no insulating material around the chimney.

(i) Explain, in terms of the particles in a metal, how heat is transferred by conduction from the inside to the outside of the metal chimney.

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(ii) Suggest one advantage of having no insulation around the chimney.

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(Total 5 marks)

Q16. The diagram shows a metal pan being used to heat water.

Energy from the gas flame is transferred through the metal pan by conduction.

Explain the process of conduction through metals.

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(Total 4 marks)

Q17. A wood burning stove is used to heat a room.

Photograph supplied by iStockphoto/Thinkstock

The fire in the stove uses wood as a fuel. The fire heats the matt black metal case of the stove.

(a) The air next to the stove is warmed by infrared radiation.

How does the design of the stove help to improve the rate of energy transfer by infrared radiation?

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(b) Burning 1 kg of wood transfers 15 MJ of energy to the stove. The stove then transfers 13.5 MJ of energy to the room.

Calculate the efficiency of the stove.

Use the correct equation from the Physics Equations Sheet.

Show clearly how you work out your answer.

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Efficiency = .................................................(2)

(c) Some of the energy from the burning wood is wasted as the hot gases leave the chimney and warm the air outside the house.

Name one other way energy is wasted by the stove.

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(d) Some people heat their homes using electric heaters. Other people heat their homes using a wood burning stove.

Give two environmental advantages of using a wood burning stove to heat a home rather than heaters that use electricity generated from fossil fuels.

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(e) The metal case of the stove gets hot when the fire is lit.

Here is some information about the stove.

Mass of metal case 100 kg

Starting temperature of metal case 20 °C

Final temperature of metal case 70 °C

Specific heat capacity of metal case 510 J/kg °C

Calculate the energy required to raise the temperature of the metal case to 70 °C.


Show clearly how you work out your answer and give the unit.

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Energy required = ..............................................................(3)

(Total 10 marks)

Q18. The diagram shows the direction of heat transfer through a single-glazed window.

(a) (i) Name the process by which heat is transferred through the glass.

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(ii) Explain how heat is transferred through the glass.

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(b) The rate of heat transfer through a window depends on the difference between the inside and outside temperatures.

The graph shows the rate of heat transfer through a 1 m2 single-glazed window for a range of temperature differences.

(i) What is the range of temperature differences shown in the graph?

From ................................................ to ................................................(1)

(ii) A student looks at the graph and concludes:

‘Doubling the temperature difference doubles the rate of heat transfer.’

Use data from the graph to justify the student’s conclusion.

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(iii) A house has single-glazed windows. The total area of the windows in the house is 15 m2.

On one particular day, the difference between the inside and outside temperatures is 20 °C.

Use the graph to calculate the total rate of heat transfer through all of the windows on this particular day.


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Rate of heat transfer = ........................................ J/s(2)

(c) A homeowner plans to replace the single-glazed windows in his home with double-glazed windows. He knows that double-glazed windows will reduce his annual energy bills.

The table gives information about the double glazing to be installed by the homeowner.

Cost to buy and install Estimated yearly savings on energy bills

Estimated lifetime of thedouble-glazed windows

£5280 £160 30 years

Explain, in terms of energy savings, why replacing the single-glazed windows with these double-glazed windows is not cost effective.

To gain full marks you must complete a calculation.

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(Total 10 marks)

Q19. The diagram shows how one type of electric storage heater is constructed. The heater has ceramic bricks inside. The electric elements heat the ceramic bricks during the night. Later, during the daytime, the ceramic bricks transfer the stored energy to the room.

(a) In winter, the electricity supply to a 2.6 kW storage heater is switched on each day between midnight and 7 am. Between these hours, electricity costs 5 p per kilowatt-hour.

Calculate the daily cost of using the storage heater.



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Cost = .................................................. p(3)

(b) Homes with electric storage heaters have a separate meter to measure the electricity supplied between midnight and 7 am. Another meter measures the electricity supplied at other times. This electricity supplied at other times costs 15 p per kilowatt-hour.

Electricity companies encourage people to use electricity between midnight and 7 am by selling the electricity at a lower cost.

Suggest why.

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(c) By 7 am, the temperature at the centre of the ceramic bricks is about 800 °C.The temperature of the outside metal casing is about 80 °C.

The ceramic bricks are surrounded by ‘super-efficient’ insulation.

Explain why.

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(d) At 7 am, the electricity supply switches off and the temperature of the ceramic bricks starts to fall. The temperature of the bricks falls by 100 °C over the next four hours. During this time, 9 000 000 J of energy are transferred from the bricks.

Calculate the total mass of ceramic bricks inside the heater.

Specific heat capacity of the ceramic bricks = 750 J/kg °C.



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Mass = .................................................. kg(2)

(Total 8 marks)

Q20. The diagram shows two thermometers. The bulb of each thermometer is covered with a piece of wet cotton wool. One of the thermometers is placed in the draught from a fan.

The graph shows how the temperature of each thermometer changes with time.

(a) Which of the graph lines, A or B, shows the temperature of the thermometer placed in the draught?

Write the correct answer in the box.

Explain, in terms of evaporation, the reason for your answer.

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(b) A wet towel spread out and hung outside on a day without wind dries faster than an identical wet towel left rolled up in a plastic bag.

Explain why.

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(Total 5 marks)

Q21.Heat exchangers are devices used to transfer heat from one place to another.

The diagram shows a pipe being used as a simple heat exchanger by a student in an investigation.

Heat is transferred from the hot water inside the pipe to the cold water outside the pipe.

(a) Complete the following sentence by drawing a ring around the correct word in the box.

Heat is transferred from the hot water inside the pipe

conduction.

to the cold water outside the pipe by convection.

radiation.

(1)

(b) The student wanted to find out if the efficiency of a heat exchanger depends on the material used to make the pipe. The student tested three different materials. For each material, the rate of flow of hot water through the pipe was kept the same.

The student’s results are recorded in the table.

Material Temperature of the cold water at the start in °C

Temperature of the cold water after 10 minutes in °C

Copper 20 36

Glass 20 23

Plastic 20 21

(i) The rate of flow of hot water through the pipe was one of the control variables in the investigation.

Give one other control variable in the investigation.

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(ii) Which one of the three materials made the best heat exchanger?

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(c) The student finds a picture of a heat exchanger used in an industrial laundry.The heat exchanger uses hot, dirty water to heat cold, clean water.

This heat exchanger transfers heat faster than the heat exchanger the student used in the investigation.

Explain why.

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(Total 6 marks)

Q22.According to kinetic theory, all matter is made up of small particles. The particles are constantly moving.

Diagram 1 shows how the particles may be arranged in a solid.

Diagram 1

(a) One kilogram of a gas has a much larger volume than one kilogram of a solid.

Use kinetic theory to explain why.

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(b) Diagram 2 shows the particles in a liquid. The liquid is evaporating.

Diagram 2

(i) How can you tell from Diagram 2 that the liquid is evaporating?

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(ii) The temperature of the liquid in the container decreases as the liquid evaporates.

Use kinetic theory to explain why.

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(Total 8 marks)

Q23.The diagram shows a car radiator. The radiator is part of the engine cooling system.

Liquid coolant, heated by the car engine, enters the radiator. As the coolant passes through the radiator, the radiator transfers energy to the surroundings and the temperature of the coolant falls.

(a) Why is the radiator painted black?

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(b) Different radiators have different numbers of cooling fins along the length of the radiator.

The sketch graph shows how the number of cooling fins affects the rate of energy transfer from the radiator.

The number of cooling fins affects the rate of energy transfer from the radiator.

Explain how.

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(c) When the car engine is working normally, 2 kg of coolant passes through the radiator each second. The temperature of the coolant falls from 112 °C to 97 °C.

Calculate the energy transferred each second from the coolant.

Specific heat capacity of the coolant = 3800 J/kg °C.


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Energy transferred each second = .............................................................. J(3)

(d) On cold days, some of the energy transferred from a hot car engine is used to warm the air inside the car. This is a useful energy transfer.

What effect, if any, does this energy transfer have on the overall efficiency of the car engine?

Draw a ring around the correct answer.

decreases the

efficiencydoes not change the

efficiencyincreases the

efficiency


........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(Total 9 marks)

Q24.Diagram 1 shows the energy transferred per second from a badly insulated house on a cold day

in winter.

Diagram 1

(a) (i) When the inside of the house is at a constant temperature, the energy transferred from the heating system to the inside of the house equals the energy transferred from the house to the outside.

Calculate, in kilowatts, the power of the heating system used to keep the inside of the house in Diagram 1 at a constant temperature.

1 kilowatt (kW) = 1 kilojoule per second (kJ/s)

...............................................................................................................

Power of the heating system = ...................................................... kW(1)

(ii) In the winter, the heating system is switched on for a total of 7 hours each day.

Calculate, in kilowatt-hours, the energy transferred each day from the heating system to the inside of the house.


...............................................................................................................

...............................................................................................................

Energy transferred each day = ...................................................... kWh(2)

(iii) Energy costs 15 p per kilowatt-hour.

Calculate the cost of heating the house for one day.

...............................................................................................................

Cost = ..............................(1)

(iv) The heating system is switched off at midnight.

The graph shows how the temperature inside the house changes after the heating system has been switched off.

Time of day

Draw a ring around the correct answer in the box to complete the sentence.

Between midnight and 6 am the rate of energy transfer from

decreases.

the house decreases then stays constant.

increases.

Give the reason for your answer.

...............................................................................................................

...............................................................................................................(2)

(b) Diagram 2 shows how the walls of the house are constructed.Diagram 3 shows how the insulation of the house could be improved by filling the air gap between the two brick walls with plastic foam.

Diagram 2 Diagram 3

U-value of the wall = 0.7 U-value of the wall = 0.3

(i) The plastic foam reduces energy transfer by convection.

Explain why.

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................(2)

(ii) Filling the air gap with plastic foam reduces the U-value of the wall.

What is meant by the term U-value?

...............................................................................................................

...............................................................................................................(1)

(c) A homeowner has part of the outside wall of her house removed and replaced with double-glazed glass doors.

U-value of the wall = 0.3

U-value of glass doors = 1.8

Explain the effect of replacing part of the outside wall with glass doors on the rate of energy transfer from the house.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

(2)(Total 11 marks)

Q25.The diagram shows the design of a solar cooker. The cooker heats water using infrared radiation from the Sun.

(a) Why is the inside of the large curved dish covered with shiny metal foil?

........................................................................................................................

........................................................................................................................(1)

(b) Which would be the best colour to paint the outside of the metal cooking pot?


black silver white


........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(c) Why does the cooking pot have a lid?

........................................................................................................................

........................................................................................................................(1)

(d) Calculate how much energy is needed to increase the temperature of 2 kg of water by 80 °C.

The specific heat capacity of water = 4200 J/kg °C.


........................................................................................................................

........................................................................................................................

........................................................................................................................

Energy = ...................................................................... J(2)

(Total 6 marks)

Q26.(a) The diagrams, X, Y and Z, show how the particles are arranged in the three states of matter.

(i) Which one of the diagrams, X, Y or Z, shows the arrangement of particles in a liquid?

Write the correct answer in the box. (1)

(ii) Which one of the diagrams, X, Y or Z, shows the arrangement of particles in a gas?

Write the correct answer in the box. (1)

(b) Draw a ring around the correct answer in each box to complete each sentence.

vibrating in fixed positions.

(i) In a gas, the particles are moving randomly.

not moving.

(1)

stronger than

(ii) In a solid, the forces between the particles are equal to the forces between

weaker than

the particles in a liquid.(1)

(c) The picture shows a puddle of water in a road, after a rain shower.

(i) During the day, the puddle of water dries up and disappears. This happens because the water particles move from the puddle into the air.

What process causes water particles to move from the puddle into the air?


condensation evaporation radiation

(1)

(ii) Describe one change in the weather which would cause the puddle of water to dry up faster.

...............................................................................................................

...............................................................................................................(1)

(Total 6 marks)

Q27.An electric immersion heater is used to heat the water in a domestic hot water tank.When the immersion heater is switched on the water at the bottom of the tank gets hot.

(a) Energy is transferred by the process of convection from the hot water at the bottom of the tank to the cooler water at the top.

Explain how.

........................................................................................................................

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........................................................................................................................(4)

(b) Complete the following sentence.

The main way the energy is transferred through the copper wall of the water tank is by

the process of ................................................................................ .(1)

(c) The immersion heater has a thermostat to control the water temperature.

When the temperature of the water inside the tank reaches 58°C the thermostat switches the heater off. The thermostat switches the heater back on when the temperature of the water falls to 50°C.

Graph A shows how the temperature of the water inside a hot water tank changes with time. The tank is not insulated.

Time in hours

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

Explain why.

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................(2)

(ii) To heat the water in the tank from 50°C to 58°C the immersion heater transfers 4032 kJ of energy to the water.

Calculate the mass of water in the tank.

Specific heat capacity of water = 4200 J/kg°C Use the correct equation from the Physics Equations Sheet.

...............................................................................................................

...............................................................................................................

...............................................................................................................

Mass = .............................................................. kg(3)

(iii) An insulating jacket is fitted to the hot water tank.

Graph B shows how the temperature of the water inside the insulated hot water tank changes with time.

Time in hours

An insulating jacket only costs £12.

By comparing Graph A with Graph B, explain why fitting an insulating jacket to a hot water tank saves money.

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................(3)

(Total 13 marks)

Q28.(a) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.

The diagram shows the structure of a vacuum flask.

A vacuum flask is designed to reduce the rate of energy transfer by heating processes.

Describe how the design of a vacuum flask keeps the liquid inside hot.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

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........................................................................................................................(6)

(b) Arctic foxes live in a very cold environment.

© Purestock/Thinkstock

Arctic foxes have small ears.

How does the size of the ears help to keep the fox warm in a cold environment?

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(Total 8 marks)

Q29.The picture shows a person taking a hot shower.

(a) When a person uses the shower the mirror gets misty.

Why?

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(3)

(b) The homeowner installs an electrically heated mirror into the shower room.

When a person has a shower, the heated mirror does not become misty but stays clear.

Why does the mirror stay clear?

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(Total 5 marks)

Q30.(a) A student used the apparatus drawn below to investigate the heating effect of an electric heater.

(i) Before starting the experiment, the student drew Graph A.

Graph A shows how the student expected the temperature of the metal block to change after the heater was switched on.

Describe the pattern shown in Graph A.

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................(2)

(ii) The student measured the room temperature. He then switched the heater on and measured the temperature of the metal block every 50 seconds.

The student calculated the increase in temperature of the metal block and plottedGraph B.

After 300 seconds, Graph B shows the increase in temperature of the metal block is lower than the increase in temperature expected from Graph A.

Suggest one reason why.

...............................................................................................................

...............................................................................................................(1)

(iii) The power of the electric heater is 50 watts.

Calculate the energy transferred to the heater from the electricity supply in 300 seconds.


...............................................................................................................

...............................................................................................................

...............................................................................................................

Energy transferred = ........................................... J(2)

(b) The student uses the same heater to heat blocks of different metals. Each time the heater is switched on for 300 seconds.

Each block of metal has the same mass but a different specific heat capacity.

Metal Specific heat capacity in J/kg°C

Aluminium 900

Iron 450

Lead 130

Which one of the metals will heat up the most?


aluminium iron lead

Give, in terms of the amount of energy needed to heat the metal blocks, a reason for your answer.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(c) A homeowner uses an electric immersion heater to heat the water in his hot water tank. The hot water tank has no insulation.

(i) Draw a ring around the correct answer to complete each sentence.

conduction.

Energy is transferred through the water by convection.

evaporation.

conduction.

Energy is transferred through the copper wall of the hot water tank by convection.

evaporation.

(2)

(ii) To keep the water in the tank hot for longer, the homeowner fits an insulating jacket around the tank. The insulating jacket costs £12 to buy.

The homeowner expects to save £16 each year from reduced energy bills.

Calculate the pay-back time for the insulating jacket.

...............................................................................................................

...............................................................................................................

Pay-back time = ........................................... years(2)

(Total 11 marks)

Q31.The diagram shows three cups A, B and C.

Energy is transferred from hot water in the cups to the surroundings.

(a) Use the correct answer from the box to complete each sentence.

condensation conduction convection

Energy is transferred through the walls of the cup by ....................................... .

In the air around the cup, energy is transferred by ........................................... .(2)

(b) Some students investigated how the rate of cooling of water in a cup depends on the surface area of the water in contact with the air.

They used cups A, B and C. They poured the same volume of hot water into each cup and recorded the temperature of the water at regular time intervals.

The results are shown on the graph.

Time in minutes

(i) What was the starting temperature of the water for each cup?

Starting temperature = ........................................ °C(1)

(ii) Calculate the temperature fall of the water in cup B in the first 9 minutes.

................................................................................................................

Temperature fall = ........................................ °C(2)

(iii) Which cup, A, B or C, has the greatest rate of cooling?

Using the graph, give a reason for your answer.

................................................................................................................

................................................................................................................(2)

(iv) The investigation was repeated using the bowl shown in the diagram.

The same starting temperature and volume of water were used.

Draw on the graph in part (b) another line to show the expected result.(1)

(v) After 4 hours, the temperature of the water in each of the cups and the bowl was 20°C.

Suggest why the temperature does not fall below 20°C.

................................................................................................................(1)

(c) (i) The mass of water in each cup is 200 g.

Calculate the energy, in joules, transferred from the water in a cup when the temperature of the water falls by 8°C.

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

Use the correct equation from Section B of the Physics Equations Sheet.

................................................................................................................

................................................................................................................

................................................................................................................

Energy transferred = ........................................ J(3)

(ii) Explain, in terms of particles, how evaporation causes the cooling of water.

................................................................................................................

................................................................................................................

................................................................................................................

................................................................................................................

................................................................................................................

................................................................................................................

................................................................................................................

................................................................................................................

(4)(Total 16 marks)

Q32.All objects emit and absorb infrared radiation.

(a) Use the correct answer from the box to complete each sentence.

dark matt dark shiny light matt light shiny

The best emitters of infrared radiation have

......................................................................... surfaces.

The worst emitters of infrared radiation have

......................................................................... surfaces.(2)

(b) Diagram 1 shows a sphere which is at a much higher temperature than its surroundings.

Diagram 1

Energy is transferred from the sphere to the surroundings.

The table shows readings for the sphere in three different conditions, A, B and C.

Condition Temperature ofsphere in °C

Temperature ofsurroundings in °C

A 70 5

B 80 0

C 90 30

In each of the conditions, A, B and C, the sphere transfers energy to the surroundings at a different rate.

Put conditions A, B and C in the correct order.


.........................................................................................................................

.........................................................................................................................(2)

(c) Diagram 2 shows a can containing water.

A student investigates how quickly a can of water heats up when it is cooler than room temperature.

Diagram 2

The student has four cans, each made of the same material, with the following outer surfaces.

dark matt dark shiny light matt light shiny

The student times how long it takes the water in each can to reach room temperature.

Each can contains the same mass of water at the same starting temperature.

(i) Which can of water will reach room temperature the quickest?


................................................................................................................

................................................................................................................

................................................................................................................

................................................................................................................(2)

(ii) Apart from material of the can, mass of water and starting temperature, suggestthree control variables for the student’s investigation.

1 ............................................................................................................

................................................................................................................

2 ............................................................................................................

................................................................................................................

3 ............................................................................................................

................................................................................................................(3)

(d) The photographs show two different foxes.

Fox A Fox B

By Algkalv (Own work) [CC-BY-3.0], © EcoPic/iStock

via Wikimedia Commons

Which fox is better adapted to survive cold conditions?

Give reasons for your answer.

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.........................................................................................................................

.........................................................................................................................(3)

(Total 12 marks)

Q33.Solid, liquid and gas are three different states of matter.

(a) Describe the difference between the solid and gas states, in terms of the arrangement and movement of their particles.

.........................................................................................................................

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.........................................................................................................................(4)

(b) What is meant by ‘specific latent heat of vaporisation’?

.........................................................................................................................

.........................................................................................................................

.........................................................................................................................

.........................................................................................................................(2)

(c) While a kettle boils, 0.018 kg of water changes to steam.

Calculate the amount of energy required for this change.

Specific latent heat of vaporisation of water = 2.3 × 106 J / kg.

Use the correct equation from Section B of the Physics Equations Sheet.

.........................................................................................................................

.........................................................................................................................

.........................................................................................................................

Energy required = .................................... J(2)

(d) The graph shows how temperature varies with time for a substance as it is heated.

The graph is not drawn to scale.

Explain what is happening to the substance in sections AB and BC of the graph.

Section AB .....................................................................................................

.........................................................................................................................

.........................................................................................................................

.........................................................................................................................

.........................................................................................................................

Section BC .....................................................................................................

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.........................................................................................................................(4)

(Total 12 marks)

M1. (a) the outside colour of the cans

1

(b) (i) 18 (°C) or 88 to 70ignore negative sign

1

(ii) 8 (°C) or 70 to 62ignore negative sign

1

(c) greater temperature difference between water and surroundings (at start)must mention temperature differenceignore just water hotteraccept energy used to heat cans initially

1

(d) black1

temperature falls the fastest (in L)accept (can L) loses more heat / cools quickeraccept heat for temperature

1

black is a good / the best / better emitter (of heat / radiation)accept converseignore black is best absorber

1[7]

M2. (a) (i) 7pmaccept 19.00 / 1900

1

(ii) 8pmaccept 20.00 / 2000

1

temperature drops more slowlyaccept heat for temperature accept line is less steep

1

(b) insulator1

conduction *1

convection *

* answers can be either way around1

(c) (i) 4 (years)1

(ii) it is the cheapest / cheaper / cheapdo not accept answers in terms of heat rising or DIY

1

has the shortest / shorter payback timedo not accept short payback time

1[9]

M3. (a) (i) as a source of thermal radiationaccept heat for thermal radiationaccept to act as the Sundo not accept sunlight alone

1

(ii) any one from:

• volume of wateraccept amount for volume

• distance between lamp and boiling tube

• initial / starting temperature of water

• same room temperaturedo not accept time or same insulation material

1

(iii) any one from:

• greater sensitivity / precision do not accept more reliable (negates mark)

• could link to a computer for (automatic) data analysis

• could take more frequent readings

• reduces instrument reading error accept more accurate do not accept easier to use on its own

1

(b) (i) acts as a control

accept to be able to make a comparisonaccept to see the differencedo not accept ‘to make it a fair test’ OWTTE on its own

1

(ii) (plastic) foam and aluminium foil1

(iii) (aluminium) foil is a poor absorber of thermal radiationaccept heat / infra red for thermal radiation

1

or (aluminium) foil is a (good) reflector of thermal radiationdo not accept ‘reflects sunlight’ on its own

(plastic) foam traps air which is a (good) insulatoraccept (plastic) foam is a poor conductor / (good) insulatordo not accept ‘the material’ is a good insulator / poor conductor

1

(c) particles vibrate with a bigger / stronger amplitude / faster / with more(kinetic) energy

accept particles vibrate moredo not accept start to vibrate only

1

energy transferred by collisions with other particlesdo not accept answers in terms offree/mobile electrons

1[9]

M4. (a) any three from:ignore reference to skewer

• (air) particles / molecules / atoms gain energy

• (air) particles / molecules / atoms move fasterdo not accept move moredo not accept move with a bigger amplitude / vibrate more

• (air) particles / molecules / atoms move apart

• air expandsdo not accept particles expand

• air becomes less dense

• warm / hot air risesdo not accept heat risesif credit is to be given for answers in terms of particles it must be clear they are air particles not gas particles

3

(b) conductionaccept conductor

1

(c) any one from:

• temperature of the potatodo not accept heat for temperature

• temperature of the surroundings / room / surface / atmosphereaccept how hot the potato / room is

• size / mass / weight / volume of the potato

• shape of the potato

• surface area of the potatopotato cut open insufficient

• nature of the surface of the potato

• type of surface it is placed on

• in a draught

• type of potato

• whether the skewers are left in or taken out1

(d) (foil) reflects heat (back towards potato)reduces heat loss is insufficientdo not accept reflects hot air

or (foil) is a poor emitter (of heat radiation)accept reduces / stops heat loss by radiationdo not accept heat is trapped

1[6]

M5. (a) (i) makes it warmer / raises the temperature

accept produces convection (current)accept makes it less dense

1

(ii) reduced or slows down1

(b) (i) electrical energy (to run the pump) must be paid foraccept electricity for electrical energyaccept electricity is needed for the pumpaccept it uses electricityaccept because of the pump

1

(ii) more useful (heat) energy is transferred into the house than the energyused to operate the pump

or reduced cost of heating the house is greater than the cost of running the (electrical) pump

or costs little to run compared to the savings madeaccept for 1 markreduces energy billsor reduced fuel costs / heating costs owttedo not accept it’s cheap

2[5]

M6. (a) conductiondo not accept conductor

1

(b) the freezerboth parts needed

greater temperature difference (between freezer and room)do not accept because it is the coldest

1

(c) any two from:

• poor absorber of heat / radiationaccept does not absorb heat poor emitter of heat / radiation is neutral

• reflects heat / radiation (from room away from fridge-freezer)

• reduces heat transfer into the fridge-freezer

• reduces power consumption of fridge-freezerdo not accept it is a bad conductor / good insulator

2[4]

M7. (a) the bigger the surface area, the faster the water cools down / temperature fallsanswers must imply rateaccept heat for temperature provided rate is implieddo not accept cools down more unless qualified

1

(b) any two from:

the ears:

• have large surface / areanot just has large ears

• radiate heataccept loses heat, but does not scoreif the reason given for heat loss is wrong

• keep blood cooler2

(c) (i) radiation1

(ii) conduction1

[5]

M8. (a) (i) silvered surfacesmore than the correct number of ticks in a row negates the mark

radiation2

plastic cap

conduction, convection (both required)

conduction convection radiation

vacuum

silvered surfaces (1)

plastic cap (1)

(ii)any mention of air or any other substance in a vacuum scores zero

because there are no particles in a vacuumaccept atoms / molecules for particlesaccept vacuum is empty spaceaccept there is nothing in a vacuumaccept there is no air / gas in the vacuum

conduction and convection need particles / mediumneed reference to both conduction and convectionaccept correct descriptions

2

(b) (i) less heat lost (to air above the heater)do not accept no heat lost

light shiny surfaces are poor emitters (of radiation)accept radiators for emittersreferences to reflection are neutral

or dull, matt surfaces are good emitters (of radiation)do not credit answers which infer reflection from the underside of the hoodignore correct reference to absorption

2

(ii) correct diagram drawn with one output arrow narrowerthan the other

ignore input

arrows correctly labelled with energy formeg

flow charts score zero2

(iii) energy cannot be destroyedaccept (principle of) conservation of energydo not accept because energy cannot be lost without clarification

1[9]

M9.(a) (i) 120, 12.5 ringed1

thermometer / stop clock misreadallow parallax errorhuman error is insufficient

1

(ii) repeat the experiment twice more to obtain 3 sets of data1

and take a mean1

(iii) because the data is recorded more frequently / continuously1

and to a greater resolution /accuracy / no reading error1

(b) there are attractive forces between moleculesaccept particles for molecules

1

only the fastest molecules have enough energy to break away from othermolecules

1

these molecules escape from the surface of the liquid1

therefore the average speed /energy of the remaining molecules goes down1

the lower the average speed /energy of molecules the lower the temperatureof the liquid

1

(c) it reduces the cooling effect1

because the rate of evaporation of sweat / water decreases1

[13]

M10. (a) because black is a good absorber of radiation1

there will be a faster transfer of energyallow the temperature of the water rises faster

1

(b) 16 800 000allow 1 mark for substitution into correct equationie 100 × 4200 × 40

2

(c) 7 allowecf from part (b)

1

(d) Marks awarded for this answer will be determined by theQuality of Written Communication (QWC) as well as thestandard of the scientific response.

No relevant content.0 marks

There is a brief description of the advantages and disadvantagesof using solar energy to heat the water rather than using anelectric immersion heater, including either advantages ordisadvantages from the examples below.

Level 1 (1-2 marks)

There is a description of some of the advantages anddisadvantages of using solar energy to heat the waterrather than using an electric immersion heater, with atleast one advantage and one disadvantage from theexamples below.

Level 2 (3-4 marks)

There is a clear, balanced and detailed description of theadvantages and disadvantages of using solar energy toheat the water rather than using an electric immersionheater, with a minimum of two advantages and twodisadvantages from the examples below.

Level 3 (5-6 marks)

examples of the points made in the response

advantages

accept specific examples of polluting gases

• a renewable energy source

• energy is free

• does not pollute the atmosphere

• no fuel is burnt

• energy can be stored (in the water)

disadvantagesaccept unreliable energy source

• only available in daylight hours

• availability fluctuates

• insufficient hours of sunlight in some countries

• average low intensity in some countries[11]

M11. (a) energy needed to produce evaporation comes from the body1

therefore this stops the body temperature rising1

(b) the silver space blanket reflects energy back to the runneraccept heat for energy

1

and this reduces the energy transferred from the body by radiation1

[4]

M12. (a) (i) 2.1correct answer only

1

(ii) 3.15ortheir (a)(i) × 1.5 correctly calculated

allow 1 mark for correct substitutionie 2.1 × 1.5ortheir (a)(i) × 1.5

2

kilowatt-houraccept kWhora substitution 2100 × 5400 scores 1 mark2100 × 5400 incorrectly calculated with answer in joules scores 2marksan answer of 11 340 000 scores 2 marksan answer of 11 340 000 J scores 3 marks

1

(iii) most (input) energy is usefully transformedaccept does not waste a lot of energyaccept most of the output / energy is usefuldo not accept it does not waste energy

1

(b) the room is losing energy / heat1

at the same rate as the heater supplies itthis mark only scores if the first is scoreddo not accept heater reaches same temperature as room / surroundingsrate of heat gain = rate of heat loss scores both marks

1[7]

M13. (a) conduction1

(b) (i) any one from:

• starting temperature (of cold water)temperature is insufficient

• pipe lengthaccept size of pipe

• pipe diameter

• pipe (wall) thickness

• volume of cold wateraccept amount for volume

• temperature of hot water (in)

• time1

(ii) (type of) material is categoricaccept one variable is categoricaccept variable(s) are categoricaccept it is categoricaccept variable(s) are not continuousdescriptions of variables ie names and numbers is insufficient

1

(iii) copper1

greatest temperature changeonly scores if copper chosenaccept heat for temperatureaccept heated water the fastestaccept it was hottest (after 10 minutes)accept it is the best / a good conductor

1

(c) larger (surface) areaaccept the pipe is longeraccept hot (dirty) water (inside pipe) is in contact with the cold water (outside pipe) for a longer timehe pipe is a spiral is insufficient

1[6]

M14. (a) (i) radiation1

(ii) traps (small pockets of) airdo not accept it’s an insulatordo not accept reduces conduction and / or convectiondo not allow it doesn’t allow heat to escape

1

(b) (i) bigger temperature difference (between the water and surroundings)at the start (than at the end)

do not accept water is hotter1

(ii) starting temperature (of the water)accept thickness of fleecedo not accept same amount of fleecedo not accept thermometer / cando not accept time is the same

1

(iii) 18 (°C)correct answer only

1

(iv) M1

smallest temperature drop (after 20 mins)cannot score if M is not chosenaccept it’s the best insulatoraccept smallest loss in heataccept keeps heat / warmth in for longer

1[7]

M15. (a) any two from:

• (air) particles / molecules / atoms gain energy

• (air) particles / molecules / atoms move fasterdo not accept move moredo not accept move with a bigger amplitude / vibrate more

• (air) particles / molecules / atoms move apart

• air expandsignore particles expand

• air becomes less denseignore particles become less dense

• warm / hot air / gases / particles risedo not accept heat risesanswers in terms of heat particles negates any of the mark points that includes particles

2

(b) (i) any two from

• free / mobile electrons gain (kinetic) energyaccept free / mobile electrons move fasteraccept vibrate faster for gain energy

• free electrons collide with other (free) electrons / ions / atoms / particles

• atoms / ions / particles collide with other atoms / ions / particlesanswers in terms of heat particles negates this mark point

2

(ii) (faster) energy / heat transfer to room(s) / houseaccept room(s) / house gets warm(er)accept lounge / bedroom / loft for rooms

1[5]

M16. accept atoms / particles for ions throughout

(a metal has) free electronsaccept mobile for free

1

(kinetic) energy of (free) electrons increasesaccept energy of ions increasesaccept ions vibrate with a bigger amplitudeaccept ions vibrate moredo not accept electrons vibrate more

1

(free) electrons move faster1

or

electrons move through metalaccept electrons collide with other electrons / ions

(so) electrons transfer energy to other electrons / ionsaccept ions transfer energy to neighbouring ions

1[4]

M17. (a) any two from:

• black is a good emitter of (infrared radiation)

accept heat for radiationignore reference to absorbing radiation

• large surface (area)

• matt surfaces are better emitters (than shiny surfaces)accept matt surfaces are good emittersignore reference to good conductor

2

(b) 90% or 0.9(0)

allow 1 mark for correct substitution, ieprovided no subsequent step shownan answer of 90 scores 1 markan answer of 90 / 0.90 with a unit scores 1 mark

2

(c) (producing) lightallow (producing) sound

1

(d) any two from:

• wood is renewableaccept wood grows again / quicklyaccept wood can be replanted

• (using wood) conserves fossil fuelsaccept doesn’t use fossil fuels

• wood is carbon neutralaccept a descriptioncheaper / saves money is insufficient

2

(e) E = m × c × θ

2 550 000allow 1 mark for correct substitutionie 100 × 510 × 50provided no subsequent step shownanswers of 1 020 000, 3 570 000 gain 1 mark

2

joules /Jaccept kJ / MJdo not accept j

for full credit the unit and numerical answer must be consistent1

[10]

M18. (a) (i) conduction1

(ii) atoms gain (kinetic) energyaccept particles / molecules for atomsdo not accept electrons for atoms

oratoms vibrate with a bigger amplitude

accept vibrate faster / moredo not accept start to vibrate

oratoms collide with neighbouring atoms

1

transferring energy to (neighbouring / other) atomsdo not accept heat for energy

ormaking these other atoms vibrate with a bigger amplitude

accept faster / more for bigger amplitudemention of (free) electrons moving and passing on energy negates this mark

1

(b) (i) 5 (°C) to 25 (°C)either order

1

(ii) a correct example of doubling temperature difference doubling heat transfer

eg going from 5 to 10 (°C) difference doubles heat transfer from 30 to 60 (J/s)accept for heat transfer number of joules / itallow 1 mark for correctly reading 1 set of data eg at 5 °C the heat transfer is 30orfor every 5°C increase in temperature difference heat transfer increases by 30 (J/s)no credit for stating they are directly proportional

2

(iii) 1800allow 1 mark for obtaining heat transfer value = 120

2

(c) payback time calculated as 33 yearscalculations must be correct to score the first mark pointexplanations must relate to it not being cost effective

1

this is greater than lifetime of windowsortotal savings (over 30 years) = £4800 (1)

this is less than cost of windows (1)or

= 176 (1)

this is more than the yearly savings (1)1

[10]

M19. (a) E = P × t

91 (p)an answer £0.91 gains 3 marksan answer 0.91 gains 2 marksallow 2 marks for energy transferred = 18.2 (kWh)orsubstitution into 2 equations combined, ie 2.6 × 7 × 5allow 1 mark for correct substitution into E = P × t, ie E = 2.6 × 7orallow 1 mark for multiplying and correctly calculating an incorrect energy transfer value by 5

3

(b) answers should be in terms of supply exceeding demandaccept there is a surplus / excess of electricity (at night)

1

(c) reduce (rate of) energy transfer (from ceramic bricks)accept heat for energydo not accept no energy / heat escapesdo not accept answers in terms of lost / losing heat if this implies heat is wasted energy

1

so keeping the (ceramic) bricks hot for longeraccept increase time that energy is transferred to the roomaccept keep room warm for longer

or

to stop the casing getting too hotaccept so you do not get burnt (on the casing)

1

(d) E = m × c × θ

120allow 1 mark for correct substitutionie 9 000 000 = m × 750 × 100

2[8]

M20. (a) Bno mark for B - marks are for the explanationfirst two mark points can score even if A is chosen

draught increases (the rate of) evaporationaccept more evaporation happensaccept draught removes (evaporated) particles fasterdo not accept answers in terms of particles gaining energy from the fan / draught

1

evaporation has a cooling effectaccept (average) kinetic energy of (remaining) particles decreases

1

so temperature will fall faster / further1

(b) larger surface area1

increasing the (rate of) evaporationaccept more / faster evaporationaccept easier for particles to evaporate

or

for water to evaporate fromaccept more particles can evaporateaccept water / particles which have evaporated are trapped (in the bag)answers in terms of exposure to the Sun are insufficient

1

[5]

M21.(a) conduction1

(b) (i) any one from:

• starting temperature (of cold water)temperature is insufficient

• pipe lengthaccept size of pipe

• pipe diameter

• pipe (wall) thickness

• volume of cold wateraccept amount for volume

• temperature of hot water (in)

• time1

(ii) copper1

greatest temperature changeonly scores if copper chosenaccept heat for temperatureaccept heated water the fastestaccept it was hottest (after 10 minutes)accept it is the best / a good conductor

1

(c) the pipe has a larger (surface) areaaccept pipe is longer

1

(so) hot / dirty water (inside pipe) is in contact with cold / clean water (outside pipe) for longer

1[6]

M22.(a) there are strong forces (of attraction) between the particles in a solidaccept molecules / atoms for particles throughout accept bonds for forces

1

(holding) the particles close togetherparticles in a solid are less spread out is insufficient

1

or

(holding) the particles in a fixed pattern / positions

but in a gas the forces between the particles are negligibleaccept very small / zero for negligible accept bonds for forces

1

so the particles spread out (to fill their container)accept particles are not close together gas particles are not in a fixed position is insufficient

1

(b) (i) particles are (shown) leaving (the liquid / container)accept molecules / atoms for particles throughoutaccept particles are escapingparticles are getting further apart is insufficient

1

(ii) accept molecules / atoms for particles throughout accept speed / velocity for energy throughout

particles with most energy leave the (surface of the) liquidaccept fastest particles leave the liquid

1

so the mean / average energy of the remaining particles goes down1

and the lower the average energy (of the particles) the lower the temperature (of the liquid)

1[8]

M23.(a) (matt) black is a good emitter of infrared / radiationaccept heat for infrared / radiationignore reference to good absorberattracts heat negates this marking point

1

to give maximum (rate of) energy transfer (to surroundings)accept temperature (of coolant) falls fast(er)accept black emits more radiation for 1 markblack emits most radiation / black is the best emitter of radiation for2 marks

1

(b) the fins increase the surface areaaccept heat for energy

1

so increasing the (rate of) energy transferorso more fins greater (rate of) energy transfer

1

(c) 114 000allow 1 mark for correct temperature change, ie 15 (°C)orallow 2 marks for correct substitution, ie 2 × 3 800 × 15answers of 851 200 or 737 200 gain 2 marksorsubstitution 2 × 3800 × 112 or 2 × 3800 × 97 gains 1 markan answer of 114 kJ gains 3 marks

3

(d) increases the efficiency1

less (input) energy is wastedaccept some of the energy that would have been wasted is (usefully) used

or

more (input) energy is usefully usedaccept heat for energy

1[9]

M24.(a) (i) 5(.0)1

(ii) 35 or their (a)(i) × 7 correctly calculatedallow 1 mark for correct substitution, ie 5 or their (a)(i) × 7 provided no subsequent step shown

2

(iii) 525(p)or(£) 5.25ortheir (a)(ii) × 15 correctly calculated

if unit p or £ given they must be consistent with the numerical answer

1

(iv) decreases1

temperature difference (between inside and outside) decreasesaccept gradient (of line) decreasesdo not accept temperature (inside) decreasesdo not accept graph goes down

1

(b) (i) air (bubbles are) trapped (in the foam)do not accept air traps heat foam has air pockets is insufficient

1

(and so the) air cannot circulate / move / form convection currentair is a good insulator is insufficient no convection current is insufficientanswers in terms of warm air from the room being trapped are incorrect and score no marks

1

(ii) how effective / good a material is as an insulator / at keeping energy inaccept heat for energy accept the lower the U-value the better the insulator accept the lower the U-value the lower the rate of energy / heat transfer

1

(c) it will increaseroom will be cooler is insufficient

1

because the glass is not (such) a good insulator (as the wall)the U-value has increased is insufficient

1[11]

M25.(a) to reflect (the infrared)accept (shiny surfaces) are good reflectorsignore reference to incorrect type of wave

1

(b) black1

best absorber (of infrared)answer should be comparativeblack absorbs (infrared) is insufficientaccept good absorber (of infrared)ignore reference to emitter ignore attracts heatignore reference to conduction

1

(c) to reduce energy lossaccept to stop energy loss accept heat for energy accept to stop / reduce convection

orso temperature of water increases faster

accept to heat water faster accept cooks food faster

orreduces loss of water (by evaporation)

1

(d) 672 000allow 1 mark for correct substitution, ie 2 × 4200 × 80 provided no subsequent step shown

2[6]

M26.(a) (i) Z1

(ii) X1

(b) (i) moving randomly1

(ii) stronger than1

(c) (i) evaporation1

(ii) any one from:

• becomes windy

• temperature increasesaccept (becomes) sunny“the sun” alone is insufficient

• less humid1

[6]

M27.(a) (water) particles / molecules gain energy / move fasteraccept atoms for moleculesignore move more do not accept move with a bigger amplitude / vibrate more

1

and (the particles / molecules) move apart

1

this causes the water to become less denseaccept water expandsignore particles become less dense

1

and the warm / hot water rises (through the tank)accept (more energetic water) particles rise to the topignore heat rises

1

(b) conduction1

(c) (i) there is a bigger temperature difference between the water and the surrounding air

accept the water is hottest / hotter1

so the transfer of energy (from hot water) is fasteraccept heat for energyignore temperature falls the fastest

1

(ii) 120allow 1 mark for converting kJ to J correctly, ie 4 032 000

or

correctly calculating temperature fall as 8°C

or

allow 2 marks for correct substitution, ie 4 032 000 = m × 4200 × 8

answers of 0.12, 19.2 or 16.6 gain 2 marks

answers of 0.019 or 0.017 gain 1 mark3

(iii) water stays hot for longer1

so heater is on for less timeaccept so less energy needed to heat water

1

so cost of the jacket is soon recovered from) lower energy costs / billsaccept short payback time

1[13]

M28.(a) Marks awarded for this answer will be determined by the Quality of Written Communication

(QWC) as well as the standard of the scientific response. Examiners should also refer to the information in the Marking guidance.

0 marksNo relevant content.

Level 1(1-2 marks)There is a basic explanation of one featureora simple statement relating reduction in energy transfer to one feature.

Level 2(3-4 marks)There is a clear explanation of one featureora simple statement relating reduction in energy transfer to two features.

Level 3(5-6 marks)There is a detailed explanation of at least two featuresora simple statement relating reduction in energy transfer to all four features.

Examples of the points made in responseextra informationaccept throughout: heat for energy loss for transfer

plastic cap:

• plastic is a poor conductoraccept insulator for poor conductor

• stops convection currents forming at the top of the flask so stopping energy transfer by convection

• molecules / particles evaporating from the (hot) liquid cannot move into the (surrounding) air so stops energy transfer by evaporation

• plastic cap reduces / stops energy transfer by conduction / convection / evaporation

glass container:

• glass is a poor conductor so reducing energy transfer by conduction

• glass reduces / stops energy transfer by conduction

vacuum:

• both conduction and convection require a medium / particles

• so stops energy transfer between the two walls by conduction and convection

• vacuum stops energy transfer by conduction / convection

silvered surfaces:

• silvered surfaces reflect infrared radiationaccept heat for infrared

• silvered surfaces are poor emitters of infrared radiation

• infrared radiation (partly) reflected back (towards hot liquid)

• silvered surfaces reduce / stop energy transfer by radiation6

(b) (the ears have a) small surface areaears are small is insufficient

1

so reducing energy radiated / transferred (from the fox)accept heat lost for energy radiateddo not accept stops heat loss

1[8]

M29.(a) any two from:

• water evaporatesaccept steam / water vapour for water moleculesaccept water turns to steam

• water molecules / particles go into the air

• mirror (surface) is cooler than (damp) airaccept the mirror / surface / glass is cold

• water molecules / particles that hit the mirror lose energyaccept water molecules / particles that hit the mirror cool down

• cooler air cannot hold as many water molecules / particles2

(causes) condensation (on the mirror)accept steam changes back to water (on the mirror)

orparticles move closer together

1

(b) mirror (surface) is warmmirror is heated is insufficient

1

(rate of) condensation reducedaccept no condensation (happens)

1[5]

M30.(a) (i) temperature (increase) and time switched on are directly proportionalaccept the idea of equal increases in time giving equal increases in temperatureanswers such as:• as time increases, temperature increases• positive correlation• linear relationship• temperature and time are proportionalscore 1 mark

2

(ii) any one from:“it” refers to the metal block

• energy transfer (from the block) to the surroundingsaccept lost for transferaccept air for surroundings

• (some) energy used to warm the heater / thermometer (itself)accept takes time for heater to warm up

• (metal) block is not insulated1

(iii) 15 000allow 1 mark for correct substitution, ie 50 × 300 provided no subsequent step shown

2

(b) leadreason only scores if lead is chosen

1

needs least energy to raise temperature by 1°Caccept needs less energy to heat it (by the same amount) lowest specific heat capacity is insufficient

1

(c) (i) convectioncorrect order only

1

conduction1

(ii) 3 / 4 (year)

or

allow 1 mark for correct method, ie shown

0.75

or

9 months

or

274 days2

[11]

M31.(a) conductionmust be in correct order

1

convection1

(b) (i) 70accept ± half a square(69.8 to 70.2)

1

(ii) 15accept 14.6 to 15.4 for 2 marksallow for 1 mark 70 − 55ecf from (b)(i) ± half a square

2

(iii) C1

biggest drop in temperature during a given timeaccept it has the steepest gradient this is a dependent

1

(iv) starting at 70 °C and below graph for Cmust be a curve up to at least 8 minutes

1

(v) because 20 °C is room temperatureaccept same temperature as surroundings

1

(c) (i) 6720correct answer with or without working gains 3 marks6 720 000 gains 2 markscorrect substitution of E = 0.2 × 4200 × 8 gains 2 markscorrect substitution of E = 200 × 4200 × 8 gains 1 mark

3

(ii) the fastest particles have enough energyaccept molecules for particles

1

to escape from the surface of the water1

therefore the mean energy of the remaining particles decreasesaccept speed for energy

1

the lower the mean energy of particles the lower the temperature (of the water)accept speed for energy

1[16]

M32.(a) dark matt1

light shiny1

(b) B A C1

biggest temperature difference (80 °C)dependent on first mark

1

(c) (i) (the can that is) dark matt1

best absorber (of infrared radiation)1

(ii) any three from:

• same area / shape of can• surrounding temperature is the same for all cans• same surface underneath cans• same position in the room

3

(d) fox A

smaller ears1

thicker fur1

these minimise energy transferdependent on first 2 marks

1[12]

M33.(a) solidparticles vibrate about fixed positions

1

closely packedaccept regular

1

gasparticles move randomly

accept particles move fasteraccept freely for randomly

1

far apart1

(b) amount of energy required to change the state of a substance from liquid to gas (vapour)

1

unit mass / 1 kgdependent on first marking point

1

(c) 41000 or 4.1 × 104 (J)accept41400 or 4.14 × 104

correct substitution of0.018 × 2.3 × 106 gains 1 mark

2

(d) ABchanging state from solid to liquid / melting

1

at steady temperaturedependent on first AB mark

1

BCtemperature of liquid rises

1

until it reaches boiling pointdependent on first BC mark

1[12]

E1. Many candidates gave incorrect answers to parts (a) and (b). It was common for candidates to misread the scales in part (b).

Part (c) was very poorly answered, with hardly any candidates scoring the mark. The significance of temperature difference is clearly not understood.

Answers to part (d) demonstrated a basic, widespread, misunderstanding of the absorption and emission of thermal energy. Most candidates stated that can L must be white but many still scored one mark for noting that can L cooled faster than can M. The main reasons for the colour decision seemed to be that white is a good reflector of heat and therefore would have kept the liquid inside cooler or that because black is a good absorber it would continue to absorb heat which would keep can M hotter.

E2. The better candidates were able to score all 3 marks in part (a). The weaker candidates failed to relate the question to the data in the graph, and were therefore putting down answers such as “The curtains were closed at 5 o’clock because that is when it gets dark”.

In part (b) most candidates were able to score at least 2 out of the 3 marks, however many candidates thought that double glazing reduced heat lost by radiation.

A pleasing number of candidates were able to carry out the calculation in part (c)(i) successfully. In part (c)(ii) candidates again tended to ignore the data in the table. This led to many answers along the lines of either “Hot air rises” or “If you don’t insulate the loft first you are wasting your money on double glazing and cavity wall insulation because of all the draughts in the loft”.

E3. The candidates were generally aware of the ideas of types of variables, control, accuracy and precision and the way that laboratory equipment can be used to simulate large scale situations. Candidates were able to demonstrate the ability to extract information from investigative results.

However, in part (b)(iii) the skill required to explain the results of the investigation was in little evidence, as was the ability to explain a facet of heat transfer in particulate terms in for part (c).

E4. Foundation Tier

(a) Many candidates appeared to be led astray by the presence of the metal skewer, and were thus basing their answers on the process of conduction. Many of the other candidates simply stated that the heat was transferred by the process of convection; as

this fact was stated in the stem of the question, they therefore gained no marks. A number of candidates wrote ‘heat rises’ rather than ‘heated air rises’ and so did not gain credit. Overall there was a disappointing response to this question.

(b) Most candidates correctly identified the process of conduction.

(c) A well-answered question, with most candidates referring either to the temperature of the room or to whether or not the skewer was removed as being the main factor influencing the rate at which the potatoes will cool down. Some candidates appeared not to understand the term ‘factor’.

(d) Some candidates offered vague answers such as “The foil traps the heat inside”. Many candidates however realised that the shiny foil will reflect the heat back into the potatoes.

Higher Tier

(a) Candidates who answered in terms of the bulk movement of air tended to score better than those who referred to particles. Although the fact that particles gained energy was correctly stated, many candidates answered in terms of the particles vibrating or expanding. Many candidates used the expression ‘heat rises’ rather than ‘heated air rises’. A significant number of candidates misinterpreted the question and explained about the conduction of heat through the skewer and potato.

(b) This was correctly answered by the majority of candidates.

(c) A well answered question with very few failing to gain a mark. A variety of responses was seen with the most popular referring to temperature of surroundings, surface area or the metal skewer.

(d) There were many good answers in terms of the heat being reflected, or the foil being a poor emitter of radiation. More general answers referring to insulation or reducing heat loss failed to score a mark.

E5. (a) (i) This was answered correctly by the majority of candidates.

(ii) Most answers involved one of three responses: no transfer of energy; transfer of energy from outside to inside; and the correct response that the energy transfer would reduce. Some candidates answered in terms of the air itself being transferred.

(b) (i) The majority of candidates realised that electricity was needed, many specifying that it was needed to operate the pump.

(ii) This question was not well answered. Many candidates did not respond to the instruction to answer in terms of cost effectiveness. Of those who answered in terms of cost, many gained a mark for saying that money would be saved on the original method of heating the house, but only a minority compared this saving to the cost of running the heat exchanger.

E6. (a) Candidates showed some confusion between conduction, convection and radiation with only just over half of the candidates gaining the mark.

(b) The majority of candidates correctly identified the freezer but less than half of these went on to give the correct reason of greater temperature difference with the others merely noting that the freezer was colder. A number of weaker candidates indicated the fridge because they thought it would be easier to raise its temperature to match the surroundings.

(c) Many candidates scored a mark for correctly identifying that the white shiny surface is a poor absorber of heat. Whilst there were many answers referring to the surface reflecting the heat, there were also answers of ‘reflecting the cold’. A few candidates seemed to think that we needed to reduce the heat loss from the fridge freezer to the room. Non-physics answers of fitting in with kitchen colour schemes and being easier to clean were fairly frequent.

E7. (a) Many candidates failed to spot that what was required was a comparison of the rate of cooling; thus answers such as ‘the large surface area cooled down more’ were common. Several candidates were not able to interpret the graph correctly, and stated that the small surface area would cool down more quickly.

(b) Many candidates failed to spot the connection between part (b) and part (a) of the question and therefore did not realise that this question was also about surface area. This mistake led to many answers such as ‘the large ears act as sunshades’ and ‘the fox is able to flap his ears to create a breeze’.

(c) (i)(ii) Both were poorly answered, with many candidates being totally confused between conduction, convection and radiation.

E8. Foundation Tier

(a) (i) Few candidates obtained any marks for completing the table.

(ii) It was surprising to find that very few candidates understand what is meant by the term ‘vacuum’. The majority of candidates believed that a vacuum contains air, and that this is what prevents the loss of heat.

(b) (i) This question was very poorly answered. Most candidates failed to read the labels on the diagram correctly, and thought that they were being asked about the lowersurface of the reflecting hood rather than the top surface. Consequently

their answers all referred to heat being reflected down onto the people sitting below.Even those candidates who did understand that they were required to answer about the top surface, failed to realise that it was the emissive properties of the surface that were important, not the absorbing or reflective properties.

(ii) It was clear that, at some centres, candidates had not come across Sankey diagrams: these candidates often simply copied the diagram of the patio heater and added labels showing the energy flow.

(iii) Very few candidates could relate this question to conservation of energy.

Higher Tier

(a) (i) Few candidates gained 2 marks, although many candidates correctly linked the silvered surfaces to reducing radiation for one mark only.

(ii) Even at Higher Tier it was surprising how many candidates did not know what a vacuum is. Many candidates gave answers in terms of the vacuum containing air, a poor conductor. Few candidates showed a good understanding of the role of particles in conduction and convection.

(b) (i) The majority of candidates scored no marks. Most answers referred to the underside of the hood reflecting heat down to the patio. Those candidates who picked up that the question was asking about the top surface sometimes scored one mark for saying that shiny surfaces were poor emitters of radiation, but most candidates were still concerned about reflection and often not even of heat but of light.

(ii) Many candidates attempted to draw a Sankey diagram and gained some credit. However the standard of the diagrams drawn tended to be poor – not using a ruler to draw straight lines and both output’s being similar in magnitude.

(iii) Many candidates quoted the law of conservation of energy. However candidates should appreciate that an answer which merely re-states the question (energy input always equals energy output) will not gain credit.

E12. (a) (i) The majority of candidates indicated that they had correctly added together 1400 and 700 to get 2100. However, a large number of candidates failed to notice that the values given were in watts and that the question asked for the answer in kilowatts.Of those who made an attempt to convert their answer, a large number of candidates were unable to do this correctly, the most common mistakes being to divide by 100 or to multiply by 1000. Another frequently seen error was an indication of 2100/1000 but then a failure to calculate this correctly.

(ii) It was pleasing to see so many correct answers to this calculation, usually by those candidates who opted to work out the energy in kilowatt-hours.Of those candidates who opted for joules, a common mistake was to multiply the power by a time of 90 minutes rather than converting to seconds.

(iii) This question was correctly answered by three fifths of the candidates. Most of the candidates who failed to score the mark had either just defined the term efficiency or had not picked up on the question asking for .‘very’ efficient.

(b) This part question was correctly answered by only a very small minority of candidates (less than one twentieth). Incorrect responses often stated that the temperature of the room had become the same as the temperature of the heater.

E13. (a) Less than half of the candidates wrote down the name of a process of heat transfer, and of those who did, the great majority opted for convection rather than conduction.

(b) (i) Most candidates appeared to know what was meant by a control variable. Several candidates lost the mark because their answer was imprecise, for example, simply stating .the temperature. was insufficient, as was ‘the temperature of the water’, had they written ‘the starting temperature of the water’ or ‘temperature of the hot water’, they would have gained a mark.

(ii) It is interesting to note that when this question is asked on an ISA paper, the majority of candidates can state the correct reason for the choice of graph. However, candidates seem unable to transfer this knowledge to a written paper. In this question, the most common answer was ‘because bar charts are much easier to understand than line graphs’. Under one fifth of candidates realised that a bar chart was the correct choice because one of the variables is categoric.

(iii) Most candidates correctly chose copper as the best material for the heat exchanger, and most were able to supply a satisfactory explanation in terms of the temperature change. Some candidates however were clearly muddled as to the difference between a conductor and an insulator, and therefore chose plastic because this material gave the smallest temperature change.

(c) There were few correct answers to the question; most candidates simply stated that the pipe was now coiled but failed to explain why this might be an advantage.

E14. (a) (i) Very few candidates gave the correct answer to this question.

(ii) Very few candidates answered this question correctly, in terms of air being trapped between the fibres of the fleece. Most candidates simply stated that the fleece was an insulator, or that the fleece lining was very thick. There are still many candidates who talk in terms of ‘heat particles’ being unable to escape.

(b) (i) Almost no correct answers were seen to this question, with the majority of candidates simply repeating the question in their answer.

(ii) The better candidates were able to deduce that the starting temperature of the water had been kept the same. However, most candidates simply referred to the temperature of the water, without stating that it was the starting temperature.

Other candidates correctly stated that the thickness of the fleece should have been kept the same: weaker candidates simply referred to the ‘amount’ of fleece, which was not sufficiently specific.

(iii) There were very few correct answers to the question. Several candidates thought that the temperature would rise during the next 20 minutes. Some candidates unfortunately failed to read the graph scale correctly and estimated a temperature of 19 °C.

(iv) Many candidates correctly identified jacket M as being the one that should be recommended. However, the reasons given for the choice were often very vague.

E15. (a) Less than half of the students were able to give a good description of convection, and nearly one third scored zero.

(b) (i) The description of conduction through the metal chimney was less well answered with just over one tenth of students gaining both marks. Few answers referred to the free electrons in the metal.

(ii) Around two thirds of students realised that the chimney would be able to heat the rooms up. Of the incorrect responses, a significant number stated that it would be cheaper not to insulate the chimney.

E16. The mechanism of conduction appeared to be only loosely understood by many students. Unfortunately, unclear or incorrect statements such as 'the particles start to vibrate' were often seen. About half of the answers referred to the metal having free electrons, but descriptions of how these played a part in conduction were often hazy, if not wrong.

E17. (a) Most students stated that matt black surfaces were good absorbers of radiation, but failed to go on to state that they were also good emitters of radiation. Many of the weaker students tried to explain the reason in terms of conduction or convection, even though the term radiation was used in the stem of the question. There is still a common misconception that ‘black attracts heat’.

(b) Although most students could select the correct equation to use, many put the numbers in

the wrong way round - possibly because they could not cope with the larger number being on the bottom of the fraction. Of those who did the arithmetic correctly, some added a spurious unit or, if they were expressing the efficiency as a percentage, simply left the answer as 90 without adding the percentage sign.

(c) Only a third of students gave a correct response of light or sound as a way in which energy is wasted from the stove. Some students seemed to have interpreted the word ‘way’ differently, and stated that some energy is lost when the door is opened.

(d) Just over a third of students scored at least one mark in this question, usually for stating that wood is a renewable resource. A common misconception was that the wood burning stove would not give off any gases that contribute to global warming.

(e) Nearly half of the students were able to calculate a correct value for the energy, but few scored all three marks because they either omitted the unit or wrote down an incorrect unit.

E18. (a) (i) Only a small minority of students (24%) were able to identify ‘conduction’ as the method of heat transfer.

(ii) This was poorly answered. Students did not appear to be able to even start to describe conduction. Convection or radiation were more often described. There were rare references to particles or atoms and the idea of energy being passed on by collision even rarer. There was a great deal of bad science, often having little to do with heat transfer. Even those students who mentioned vibrations of atoms or particles, suggested that the particles ‘started to vibrate’ as the process started, apparently not realising that they were already vibrating. Few marks were awarded in this question.

(b) (i) Most students gained this mark.

(ii) This was generally well done. Students found it easy to extract data correctly from the graph in order to demonstrate the truth of the statement given in the question. Some students however, tried to answer the question without using any numerical data and consequently simply repeated the question in their own words.

(ii) Many students appeared to ignore the graph and performed a calculation based upon the two quantities given in the question i.e. the area and the temperature. Those students that used the graph were often able to find the rate of heat transfer at 20°C (120 J/s) but did not realise that this was for 1 square metre. These students scored one mark. However, it was pleasing to see others go on to gain full credit for calculating the total rate of heat transfer for the full window. A significant minority (15%) did not attempt this question.

(c) This question was reasonably well done and students seemed to have a good knowledge of pay-back time and the economics of fitting double glazing. Many students managed a correct calculation and then went on to give an acceptable reason why this particular situation was not cost-effective. The most common method was to calculate the savings over 30 years (£4 800) and to conclude that this was less than the cost of installation

(£5 280), giving a ‘loss’ of £480. There were however, students who did not address the question but simply described how double glazing works and others who had perhaps performed a calculation but given no evidence on their scripts. The latter group should be made aware that for full credit a complete answer is required.

E19. (a) Many students gained full credit, or at least two marks, for calculating energy as 18.2 kWh. The most common errors were to use an incorrect time, six hours being popular and / or to calculate cost by dividing 18.2 by 5.

(b) This was very poorly answered, with just under a tenth of students scoring the mark. Most students simply repeated the stem of the question and added that it was for the electricity companies to make more money. Few students realised the significance of a lower cost and the surplus of energy at night.

(c) This was poorly answered with two-thirds of students scoring zero. Many students seemed to think that the purpose of the super-efficient insulation was to completely stop any energy / heat transfer to the room. These students seem not to understand the purpose of room heaters!

(d) Nearly half of the students scored both marks. However, all students should be encouraged to copy the equation from the equation sheet and then substitute figures. If this is done correctly, students will score at least one mark. There were a significant number of errors made in transforming the equation. Students showing only an incorrect transformation gained no credit. A significant minority of students used a temperature change other than the 100 °C given.

E20. (a) Very few students showed an understanding of evaporation. Many students thought that the fan must be blowing hot air onto the thermometer, and therefore chose thermometer A. Others chose thermometer B but thought that this was because the air from the fan was colder than the surrounding air.

(b) This part was also badly answered. Many students thought that ‘the Sun would not get through the plastic Many’. bag others failed to notice that the towel was hung outside on a day without wind, and were stating that the towel in the bag would remain wet because there was no wind.

E21.(a) Only a minority of students gained the mark here. Most thought that heat was transferred through the pipe by convection.

(b) (i) Many students were able to correctly identify one other control variable – 'starting temperature' being the favourite.

(ii) Most chose 'copper' as the material to make the best heat exchanger, but fewer managed a suitable explanation for their choice. Simply quoting figures from the data, 'copper reached 36°C', is not enough for any credit.

(c) It was apparent that many students did not understand what was happening inside the industrial heat exchanger. There were more blank responses in this question than any other on the paper. Some thought that the coil was a heating element whilst others thought that it moved or spun round. 'It's industrial so it's better' was a common answer. Many thought that the purpose of the coil was to make the water flow faster. Few answers gained both marks.

E22.(a) Whilst many answers referred to the arrangement of particles in solids and gases, fewer responses referred to the forces between the particles.

(b) (i) Just under half of the students answered correctly in terms of particles leaving the container / liquid. Other answers seen just referred to the particles ‘rising.’

(ii) Many answers referred to particles needing energy to escape, but often just stated ‘gaining energy’, without specifying that they had more energy than the particles that remained. Very few students gained the second marking point because they did not refer to “mean / average” energy. A fair number of students gained the third mark by linking a decrease in energy to the decrease in temperature.

E23.(a) Many students are unable to distinguish between a hot object emitting infrared radiation, and a cold object absorbing it. However, by stating that matt black objects are good emitters and absorbers, many were able to achieve one mark.

(b) This question was answered well, with over half of the responses correctly stating a relationship between the number of fins and the rate of energy transfer; of these responses, about half also referred to the increased surface area.

(c) The majority of students were able to substitute the correct numbers into the correct equation and perform the calculation. Common mistakes were converting the 2 kg mass to grams, and not calculating the difference between 97 and 112 correctly.

(d) Some very pleasing answers were seen, students clearly expressing that energy which would have been wasted had now been converted into useful energy.

E24.(a) (i) Many students left this part blank. Around half of the students obtained the correct answer of 5 (kW) and they were often able to go on and obtain both marks in part (ii).

(ii) Many students left this part blank.

(iii) Many students left this part blank. This part caused more difficulty with students commonly multiplying the cost per kWh by the days or by 24. Those failing to calculate part (i) correctly often went on to gain credit with the error carried forward into the other two parts although for part (iii), correct answers for part (ii) were sometimes ignored for another quantity. Perhaps this was due to the students not

recognising how the parts were connected.

(iv) Whilst many students scored the first mark for saying that the rate of energy transfer from the house decreases, only a handful gained the second. Most simply stated the temperature dropped over the time period in question. A sizeable minority chose the second option for the first marking point, saying that between 5.30 and 6.00 am the graph did not change.

(b) (i) Most students found this difficult. “Hot air being trapped in the cavity” or “heat being trapped in the air bubbles” were common incorrect responses. Many simply repeated that energy transfer by convection would be reduced, which they were told in the stem of the question.

(ii) Many students were not able to give an indication that they understood the idea of U-value. Often they simply tried to substitute a word for U e.g. “ultimate value” or “ultra value”. Others were influenced by the word 'value' and related it to economics in some way.

(c) A major misconception of many students is that double-glazing is the best form of thermal insulation. Therefore many answered with statements like 'the rate would fall because glass is such a good insulator'. Others thought that 'heat would be trapped by the vacuum between the panes of glass'. Yet others obviously did not understand the term 'energy transfer'.

E25.(a) Most students realised that a shiny surface would be a good reflector, but many used the word “bounce” instead of “reflect”. The most common wrong response was to say that metals are good conductors.

(b) Although most students correctly chose black as the best colour to paint the outside of the metal cooking pot, there was much confusion as to the reason. Many students stated that black was the best colour to attract the Sun. Some students stated that black would absorb energy without making any comparison, e.g. by stating that black is a good absorber. As in previous papers there was much confusion between absorption and emission.

(c) The great majority of students could give a correct reason for having a lid: usually to keep the heat in or to stop the water evaporating.

(d) The majority of students could correctly complete the calculation. Some however, although they could correctly substitute the numbers into the appropriate equation, were unable to calculate the correct value. This may have been either because they did not have a calculator or they were unable to use the calculator correctly. Some students incorrectly chose to convert the mass in kilograms into grams before doing the calculation.

The correct numerical answer was 672000. Some students sensibly wrote this as 672,000 using a comma as a separator. Others wrote it as 672’000 using an apostrophe as a separator.

E26.(a) (i) Nearly all students answered this correctly.

(ii) Nearly all students answered this correctly.

(b) (i) Nearly all students answered this correctly.

(ii) Nearly all students answered this correctly.

(c) (i) The majority of students correcty chose evaporation.

(ii) Most students knew that if the weather became warmer or more windy the puddle of water would evaporate faster. A few students were unspecific and simply wrote “temperature” or “the Sun”.

E27.(a) Less than half of the students scored at least two marks, usually for referring to the hot water becoming less dense and therefore rising. Students who referred to water particles often mistakenly referred to them ‘vibrating more’ as a result of the energy given, or to the particles themselves becoming less dense.

(b) Nearly three quarters of the students correctly identified the process of conduction.

(c) (i) Fewer than one fifth of the students realised that this question related to the greatest difference in temperature between the water and the surroundings.

(ii) A small minority of the students scored full marks. The majority of students failed to convert kJ to J. Many students were unable to transpose the equation correctly.

(iii) This was very well answered, with over half of the students scoring at least two of the three marks. This was usually for realising that the insulating jacket would keep the water hotter for longer, thus requiring the heater to be switched on for a shorter period of time. Many did not score the third mark because they merely repeated the question by saying that this ‘saves money’ rather than referring to the cost of electricity / energy used.

E28.(a) This question incorporated the assessment of the Quality of Written Communication. The responses were, on the whole, disappointing. Many tried to answer this item without even mentioning conduction, convection or radiation. A sizeable minority simply listed the labelled parts of the diagram and after each stated that they stopped heat movement without stating what method of heat transfer was being affected or what it was about the component that was useful in this regard. It was obvious that many did not know what a vacuum was.

(b) Only half of the students scored any marks on this question. Many appeared to know what was going on here but could not make their ideas clear enough to gain marks. “Surface area” was often missed out. Other students suggested that it was “cold” that was moving rather than “energy” or “heat”. Common errors included “small ears made covering by fur easier”, “small ears wouldn't flap and cool down the fox” and “small ears enabled the fox to hold them close to their body for warmth”.

E29.(a) This question discriminated well, with the best students scoring all three marks. However, there was much confusion about terminology with the terms condensation, convection and evaporation apparently interchangeable in many answers. The most common way of gaining a mark was to say that condensation was occurring. The verb “to condensate” was almost universal.

(b) Most students realised that condensation would not take place, although condensation followed by evaporation from the mirror surface was common. Many thought that warm air was “attracted” to a cold surface. Others did not state that the mirror was warm and simply repeated the “heated mirror” from the stem of the question. As in part (a) the meaning of “evaporation” and “condensation” was not clear.

E30.(a) (i) Although most students could describe the pattern as being linear, very few referred

to the fact that the graph showed direct proportionality.

(ii) There were very few correct answers to this question. A few suggested it took time for the heater to warm up but other acceptable answers were rarely seen. Many stated that the difference was because the first graph was a “guess” and the second was a “real” result. There was a lot of discussion about the original room temperature and some thought that since the student was reading the temperature every 50s, they had to switch off the heater whilst they were doing this.

(iii) The majority of students could correctly complete the calculation to find the energy transferred.

(b) The majority of students chose aluminium rather than lead, presumably because it had the highest specific heat capacity. Of those who did select lead, very few were able to provide an adequate reason.

(c) (i) Most students were able to score both marks in this question.

(ii) There were few correct answers to this question. The most common method was to multiply the two numbers and thereby end up with a figure of 192 years for the pay-back time.

E31.(a) Nearly all students recognised two situations that represented conduction and convection.

(b) (i) Almost all students were able to read the starting value of temperature from a cooling curve.

(ii) Nearly all students correctly calculated the temperature fall from the cooling curve. Those who got it wrong gave the value of the temperature reached rather than the change in temperature.

(iii) The given graph showed the cooling curves for three cups of different cross-sectional areas. Students were asked which cup showed the greatest rate of cooling. Only half of the students were able to give a reason because they did not refer to temperature drop in a given time.

(iv) A diagram of a fourth container was given and students had to draw the expected cooling curve on the same axes. This was well done with four-fifths of students scoring full marks.

(v) Nearly all students recognised that the lowest temperature reached after four hours was also room temperature.

(c) (i) The calculation of energy transferred from the water, where the mass of water was given in grams, was correctly done by two-thirds of the students.

(ii) The explanation of evaporation causing the cooling of water was very poorly answered with half of the students scoring zero marks. Many students described convection and very few referred to the reduction in the mean energy of the particles when the most energetic had escaped from the surface of the water. Only a tenth of students scored three or four marks.

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Web viewEach word may be used once or ... The heat exchanger uses heat from the air outside to warm the inside ... Heat exchangers are devices used to transfer heat from