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P1 05 Efficiency and Transfer

233 minutes

233 marks

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(a) In Britain most power stations burn fuel to produce heat. The diagram shows the stages by which the heat is transferred into electrical energy.Complete the diagram by filling in the missing word.

Water heated to produce steam → Steam turns

a turbine →Turbine turns a coil in a

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

→ Electricity is produced

(1)

(b) A fuel burning power station uses 2000 joules of fuel energy to generate 600 joules of electrical energy. The rest of the fuel energy is wasted as heat.

(i) For every 600 joules of electrical energy generated, how much fuel energy is wasted as heat?

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

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

(ii) Use the following equation to calculate the efficiency of the power station.Show clearly how you work out your answer.

efficiency =

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

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

efficiency = ......................................................................(2)

(c) List A gives three energy resources used to generate electricity. List B gives

environmental problems that may be caused by using different energy resources. Draw a straight line from each energy resource in List A to the environmental problem it may cause in List B. Draw three lines only.

(3)

(d) A small wind generator is used to charge a battery. The graph shows the power output of the generator at different wind speeds.

(i) What is the maximum power produced by the generator?

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

(ii) The generator is designed to stop if the wind speed is too high.

At what wind speed does the generator stop working?

.................................................................................................................... m/s(1)

(iii) Give one disadvantage of using a wind generator to charge a battery.

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

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

(Total 10 marks)

Q2. (a) The drawing shows the energy transferred each second by a television set.

(i) What form of energy is transferred as waste energy by the television set?

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

(ii) What effect will the waste energy have on the air around the television set?

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

(iii) Use the following equation to calculate the efficiency of the television set.

efficiency =

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

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

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

(b) The diagrams show the energy transferred each second for three different types of lamp. For each lamp the electrical energy input each second is 100 joules.

Which type of lamp is the most efficient?

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

Give a reason for your choice.

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

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

(Total 6 marks)

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(a) The table gives information about some ways of reducing the energy consumption in a house.

Method of reducing energy Installation Annual saving on

consumption cost in £ energy bills in £

Fit a new hot water boiler 1800 200

Fit a solar water heater 2400 100

Fit underfloor heating 600 50

Fit thermostatic radiator valves 75 20

Which way of reducing energy consumption is most cost effective over a 10-year period?

To obtain full marks you must support your answer with calculations.

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

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

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

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

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

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

(b) Explain why using an energy-efficient light bulb instead of an ordinary light bulb reduces the amount of carbon dioxide emitted into the atmosphere.

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

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

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

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

(Total 5 marks)

Q4. (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?

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

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

What time do you think the curtains were closed?

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

Give a reason for your answer.

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

(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

billsPayback time

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.

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

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

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

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

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

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

(Total 9 marks)

Q5. (a) The picture shows a new washing machine.

Complete the following sentence using one of the words in the box.

kinetic light sound

A washing machine is designed to transform electrical energy into heat and

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

(b) The instruction booklet for the washing machine contains the following information.

Wash cycle Average powerduring cycle

Time taken torun cycle

HOT 1.5 kW 2 hours

COOL 1.1 kW 1½ hours

FAST 1.0 kW ¾ hour

(i) Use the following equation to calculate the energy transferred, in kilowatt-hours, to the washing machine during the HOT wash cycle. Show how you work out your answer.

energy transferred = power × time

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

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

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

(ii) Why does it cost more to use the washing machine on the HOT cycle than on the COOL or FAST cycle?

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

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

(iii) Before buying a washing machine, a householder researched several makes to find out which washing machine was the most energy efficient.

Write down one way that he could have done this research.

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

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

(Total 5 marks)

Q6. (a) The diagram shows how much heat is lost each second from different parts of an uninsulated house.

(i) Each year, the house costs £760 to heat.

How much money is being wasted because of heat lost through the roof?

Show clearly how you work out your answer.

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

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

(ii) Insulating the loft would cut the heat lost through the roof by 50 .

The loft insulation has a payback time of years.

How much did the loft insulation cost to buy?

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

Cost of loft insulation = £ .................................................(1)

(b) What happens to the wasted energy?

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

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

(Total 4 marks)

Q7. The pictures show six different household appliances.

(a) Four of the appliances, including the fan heater, are designed to transform electrical energy into heat.

Name the other three appliances designed to transform electrical energy into heat.

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

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

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

(b) Complete the following sentence using one of the words from the box.

chemical heat kinetic sound

Energy that is not usefully transformed by the fan heater is wasted as

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

(c) The table gives information about two different fan heaters.

Useful energy

transferred eachsecond in joules

Wasted energytransferred eachsecond in joules

Fan heater L 1200 10

Fan heater M 1200 20

Complete the following sentence by drawing a ring around the line in the box that is correct.

Fan heater L

is more efficient than

has the same efficiency as

fan heater M.

is less efficient than

(1)(Total 5 marks)

Q8. (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?

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

(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.

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

(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?

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

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

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

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

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

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

(Total 5 marks)

Q9. The diagram shows the label from a new freezer.

(a) An old freezer has an energy consumption per year of 350 kWh.

Use the equation in the box to calculate the extra cost of using the old freezer for one year compared with using a new ‘A’ rated freezer.

total cost = number of kilowatt-hours × cost per kilowatt-hour

Assume 1 kilowatt-hour (kWh) of energy costs 12 p.


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

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

Extra cost per year = £ ..............................(2)

(b) The price of the new freezer was reduced in a sale.

Reducing the price reduces the payback time for replacing the old freezer from 12 years to 9 years.

Calculate, in pounds, how much the new freezer was reduced in the sale.


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

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

Price reduced by = £ ........................................(2)

(c) An advertisement in a shop claims that:

‘Replacing an old freezer with a new ‘A’ rated freezer will benefit the environment.’

Do you agree that replacing the freezer will benefit the environment?

Answer yes or no. ..............................

Explain the reasons for your answer.

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

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

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

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

(Total 6 marks

Q10. (a) The diagram shows the energy transformations produced by a TV.

(i) Use the information in the diagram and the equation in the box to calculate the efficiency of the TV.

efficiency =


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

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

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

(ii) What eventually happens to the useful energy transferred by the TV?

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

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

(b) Electrical appliances left on standby use energy.

The bar chart shows the power for the appliances that one family leaves on standby when they go on holiday.

The family is on holiday for a total of 175 hours.

(i) Use the information in the bar chart and the equation in the box to calculate the energy wasted by leaving the compact stereo on standby while the family is onholiday.

energy transferred(kilowatt-hour, kWh)

= power(kilowatt, kW)

× time(hour, h)


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

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

Energy wasted = .............................. kilowatt-hours(2)

(ii) Electricity costs 12 p per kilowatt-hour.

Use the equation in the box to calculate the cost of leaving the compact stereo onstandby while the family is on holiday.



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

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

(c) A headline from a recent newspaper article is shown below.

Explain why leaving appliances on standby damages the environment.

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

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

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

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

(Total 8 marks)

Q11. The diagram shows the energy transformations produced by a TV.

(a) Use words from the diagram to complete the following sentence.

The TV is designed to transform ............................................................ energy into

light and ................................................................... energy.(2)

(b) Which one of the following statements is false?

Put a tick ( ) in the box next to the false statement.

The energy transformed by the TV makes the surroundings warmer.

The energy transformed by the TV becomes spread out.

The energy transformed by the TV will be destroyed. (1)

(c) Two different makes of television, A and B, transform energy at the same rate.Television A wastes less energy than television B.

Complete the following sentence by drawing a ring around the correct line in the box.

Television A has

a higher efficiency than

the same efficiency as

a lower efficiency than

television B.

(1)(Total 4 marks)

Q12. The pictures show three different types of electric heater.

(a) The ceramic heater is run on full power for 5 hours.

Use the following equation to calculate, in kilowatt-hours, the amount of energy transferred from the mains to the heater.



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

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

Energy transferred = .............................. kilowatt-hours(2)

(b) Which heater will be the most expensive to run on its highest heat setting?

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

(c) A heater is needed for a small office.

Comparing each type of heater with the other two, give one advantage of using each type of heater in the office.

oil-filled panel heater .................................................................................................

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

fan heater ....................................................................................................................

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

ceramic heater .............................................................................................................

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

(Total 6 marks)

Q13. 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.

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

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

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

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

(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.

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

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

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

(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.

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

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

(Total 9 marks)

Q14. The picture shows a solar-powered aircraft. The aircraft has no pilot.

Photo by NASA.

(a) Use words from the box to complete the following sentence.

electrical heat light sound

Solar cells are designed to transform .............................................................. energy into

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

(b) On a summer day, 175 000 joules of energy are supplied to the aircraft’s solar cells every second. The useful energy transferred by the solar cells is 35 000 joules every second.

(i) Use the equation in the box to calculate the efficiency of the solar cells.


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

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

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

(ii) What happens to the energy that is not usefully transferred by the solar cells?

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

(c) The aircraft propellers are driven by electric motors. As well as the solar cells, there are fuel cells that provide additional power to the electric motors.

(i) Suggest one advantage of the aircraft having fuel cells as well as the solar cells.

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

(ii) Give one environmental advantage of using electric motors to drive the aircraft propellers rather than motors that burn a fuel.

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

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

(iii) Eventually, the designers want to produce an unmanned aircraft that can fly at twice the height of a passenger jet for up to six months.

Suggest one possible use for an aircraft such as this.

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

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

(Total 8 marks)

Q15. The picture shows a food processor, which is used to grate, shred, liquidise and mix food.The table gives some information about the food processor.

Energy input Electrical

Useful energy output Kinetic

Power rating 1200 watts

Efficiency 0.8

(a) The food processor is used for a total of 30 minutes a day.

Calculate the cost of the energy wasted by the food processor each day.

Electricity costs 15 p per kilowatt-hour.

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

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

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

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

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

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

Cost of waste energy = ...................................... p(4)

(b) Explain what happens to the waste energy.

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

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

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

(Total 6 marks)

Q16. (a) The block diagram shows the important parts of a coal burning power station.

Use words from the box to complete the block diagram

boiler condenser furnace generator(2)

(b) The diagram shows the energy transformations in a coal burning power station.

Calculate the efficiency of the power station.Write down the equation you use, and then show clearly how you work out your answer.

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

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

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

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

(c) Draw a ring around the correct answer to complete the following sentence.

If fewer coal burning power stations are used to generate electricity the amount of

decrease.

not change.

increase.

carbon dioxide emitted into the atmosphere will

(1)

(d) Some types of power station generate electricity by burning a biofuel.

Give one example of a biofuel.

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

(e) Nuclear power stations generate electricity without burning a fuel.

Name the process by which a nuclear fuel provides the energy needed to generate electricity.

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

(Total 7 marks)

Q17. The farmers in a village in India use solar powered water pumps to irrigate the fields.

On average, a one square metre panel of solar cells receives 5 kWh of energy from the Sun each day.The solar cells have an efficiency of 0.15

(a) (i) Use the following equation to calculate the electrical energy available from a one square metre panel of solar cells.


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

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

Electrical energy = ................................................... kWh(2)

(ii) On average, each solar water pump uses 1.5 kWh of energy each day.

Calculate the area of solar cells required by one solar water pump.

Area = ......................................................... square metres

(1)

(b) Give one reason why the area of solar cells needed will probably be greater than the answer to part (a)(ii).

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

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

(Total 4 marks)

Q18. The picture shows a new washing machine. When the door is closed and the machine switched on, an electric motor rotates the drum and washing.

(a) Complete the following sentences.

(i) An electric motor is designed to transform electrical energy into

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

(ii) Some of the electrical energy supplied to the motor is wasted as

....................................... energy and ...................................... energy.(1)

(b) What happens to the energy wasted by the electric motor?

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

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

(c) The diagram shows the label from the new washing machine.

An ‘A’ rated washing machine is more energy efficient than a ‘C’ rated washing machine.

Explain what being more energy efficient means.

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

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

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

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

(d) The graph shows that washing clothes at a lower temperature uses less energy than washing them at a higher temperature. Using less energy will save money.

(i) Electricity costs 12 p per kilowatt-hour (kWh).The temperature setting is turned down from 40 °C to 30 °C.

Use the graph and equation in the box to calculate the money saved each wash

cycle.



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

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

Money saved = .................................................. p(2)

(ii) Suggest why reducing the amount of energy used by washing machines could reduce the amount of carbon dioxide emitted into the atmosphere.

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

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

(Total 8 marks)

Q19. (a) The diagram shows a solar powered device being used to recharge a mobile phone.

On average, the solar cells produce 0.6 joules of electrical energy each second.The solar cells have an efficiency of 0.15.

(i) Use the following equation to calculate the average energy input each second to the device.


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

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

Average energy input each second = .................................... J/s(2)

(ii) Draw a labelled Sankey diagram for the solar cells.The diagram does not need to be drawn to scale.

(1)

(iii) Energy from the Sun is stored by a rechargeable battery inside the device.

Suggest one factor that would affect the time it takes to fully charge the battery.


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

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

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

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

(b) Scientists have developed a new type of solar cell with an efficiency of over 40 %.The efficiency of the solar cell was confirmed independently by other scientists.

Suggest why it was important to confirm the efficiency independently.

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

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

(c) The electricity used in homes in the UK is normally generated in a fossil fuel power station.

Outline some of the advantages of using solar cells to generate this electricity.

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

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

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

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

(Total 8 marks)

Q20. A person uses a stairlift to go upstairs. The stairlift is powered by an electric motor.

The Sankey diagram shows the energy transfers for the electric motor.

(a) Complete the following sentence.

The electric motor wastes energy as .............................................. energy.(1)

(b) Use the equation in the box to calculate the efficiency of the electric motor.


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

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

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

(Total 3 marks)

Q21. The diagram shows a small-scale, micro-hydroelectricity generator which uses the energy of falling river water to generate electricity. The water causes a device, called an Archimedean screw, to rotate.The Archimedean screw is linked to the generator by a gearbox.

(a) Each second, the micro-hydroelectricity generator transforms 80 000 joules of gravitational potential energy into 60 000 joules of electrical energy.

(i) Fill in the missing word to complete the energy transformation diagram.

Gravitational potentialenergy of the falling water

................................ energy

Electrical energygenerated

of the Archimedean screw

(1)

(ii) Use the equation in the box to calculate the efficiency of the micro-hydroelectricitygenerator.


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

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

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

(b) The power output from a conventional large-scale hydroelectric power station is 100 000 times more than the power output from a micro-hydroelectric system.

Give one disadvantage of a conventional large-scale hydroelectric power station compared to the micro-hydroelectric system.

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

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

(c) The electricity generated by a micro-hydroelectric system is transferred via a transformer directly to local homes. The electricity generated by a conventional large-scale hydroelectric power station is transferred to the National Grid, which distributes the electricity to homes anywhere in the country.

(i) What is the National Grid?

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

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

(ii) Explain why transferring the electricity directly to local homes is more efficient than using the National Grid to distribute the electricity.

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

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

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

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

(Total 7 marks)

Q22. A homeowner had a new gas boiler installed.

(a) The following information is an extract from the information booklet supplied with the boiler.

Fuel Natural Gas

Water temperature 60 °C

Energy supplied to gas boiler 8.0 kJ/s (8.0 kW)

Efficiency 0.95

(i) Use the equation in the box to calculate the energy transferred each second by the gas boiler to the water inside the boiler.


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

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

Energy transferred by the gas boiler each second = ..................... kJ(2)

(ii) The energy value of the gas used in a home is measured in kilowatt-hours (kWh).

The homeowner has a pre-payment meter and pays £30 into his account. With a pre-payment meter, gas costs 15p per kilowatt-hour.

Use the equations in the box to calculate the total number of hours that the gas boiler would operate for £30.




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

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

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

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

Number of hours = ..................................................(2)

(b) Although the gas boiler is very efficient, some energy is wasted.

Explain what happens to the waste energy.

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

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

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

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

(Total 6 marks)

Q23. (a) The diagram shows the energy transformations produced by a television.

When the television is working, 1200 joules of energy are supplied to the television every second. The useful energy transferred by the television is 720 joules every second.

(i) Use the equation in the box to calculate the efficiency of the television.


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

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

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

(ii) Use one word from the diagram to complete the following sentence.

The electrical energy that is not usefully transformed by the television is wasted as

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

(b) Drawn below are the Sankey diagrams for three televisions, J, K and L.The diagrams are drawn to the same scale.

J

K

L

Which one of the televisions, J, K or L, is the most efficient?

Write your answer in the box.


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

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

(c) A homeowner is sent an electricity bill every 3 months. The total amount of electrical energy used during one 3-month period was 800 kilowatt-hours.Electrical energy costs 15p per kilowatt-hour.

Use the equation in the box to calculate the cost of the energy transferred from the mains electricity supply.


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

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

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

Cost = ..................................................(2)

(Total 7 marks)

Q24. 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?

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

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

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

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

(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.


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

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

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

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.

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

(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.

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

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

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

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

(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.

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

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

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

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

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

(Total 10 marks)

Q25. The appliances shown below transfer electrical energy to other types of energy.

(a) The vacuum cleaner is designed to transfer electrical energy to kinetic energy.

Three more of the appliances are also designed to transfer electrical energy to kinetic

energy. Which three?

Draw a ring around each correct appliance.3

(b) Which two of the following statements are true?

Tick ( ) two boxes.

Appliances only transfer part of the energy usefully.

The energy transferred by appliances will be destroyed.

The energy transferred by appliances makes the surroundings warmer.

The energy output from an appliance is bigger than the energy input.

(2)(Total 5 marks)

Q26. The table gives data about two types of low energy bulb.

Type of bulb Power inputin watts

Efficiency Lifetimein hours

Cost ofone bulb

Compact FluorescentLamp (CFL)

8 20% 10 000 £3.10

Light Emitting Diode(LED)

5 50 000 £29.85

(a) Both types of bulb produce the same useful power output.

(i) Calculate the useful power output of the CFL.



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

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

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

Useful power output = ................................................. W(2)

(ii) Calculate the efficiency of the LED bulb.



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

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

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

Efficiency = ......................................................(1)

(b) Sketch and label a Sankey diagram for the CFL.

(2)

(c) LED bulbs are expensive. This is because of the large number of individual electronicLED chips needed to produce sufficient light from each bulb.

(i) Use the data in the table to evaluate the cost-effectiveness of an LED bulb compared to a CFL.

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

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

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

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

(ii) Scientists are developing brighter and more efficient LED chips than those currently used in LED bulbs.

Suggest one benefit of developing brighter and more efficient LED chips.

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

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

(Total 8 marks)

Q27. (a) The Sankey diagram for a low energy light bulb, known as a CFL, is shown below.

(i) What is the useful energy output that the CFL is designed to produce?

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

(ii) What effect does the waste energy output have on the surrounding air?

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

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

(iii) Use the information in the diagram to calculate the efficiency of the CFL.



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

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

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

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

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

(iv) CFLs contain mercury. Mercury is a poisonous substance.

It is important that old CFLs are sent for recycling and not thrown into a rubbish bin.

Suggest one reason why.

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

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

(b) A new type of low energy bulb uses light emitting diodes (LEDs).

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

LED bulbs are more efficient than CFLs. This means that LED bulbs

a smaller

waste the same proportion of the input energy compared to CFLs.

a bigger

(1)

(c) The graph shows how the outside surface temperatures of a CFL and an LED bulb change after they are switched on.

Apart from a higher efficiency, suggest one advantage of using an LED bulb rather than a CFL.

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

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

(d) At the moment, LED bulbs are much more expensive to buy than CFLs.

Which two of the following would a homeowner need to know to decide whether it would be cost-effective to replace a CFL with an equally bright LED bulb?

Tick ( ) two box.

The number of hours each bulb lasts before needing to be replaced

The power of each bulb in watts

The voltage of the mains electricity supply

(1)(Total 8 marks)

Q28.(a) Solar energy is a renewable energy source used to generate electricity.

(i) What is meant by an energy source being renewable?

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

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

(ii) Name two other renewable energy sources used to generate electricity.

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

2 ...............................................................................................................(1)

(b) A householder uses panels of solar cells to generate electricity for his home.The solar cells are tilted to receive the maximum energy input from the Sun.

The data in the table gives the average energy input each second (in J/s), to a 1 m2 area of solar cells for different angles of tilt and different months of the year.

Month

Angle of tilt

20° 30° 40° 50°

February 460 500 480 440

April 600 620 610 600

June 710 720 680 640

August 640 660 640 580

October 480 520 500 460

December 400 440 420 410

(i) Use the data in the table to describe how the average energy input to the solar cells depends on the angle of tilt.

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

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

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

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

(ii) The total area of the solar cell panels used by the householder is 5 m2.

The efficiency of the solar cells is 0.18.

Use the equation in the box to calculate the average maximum electrical energy available from the solar cell panels each second in June.


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

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

Maximum energy = ............................................... joules/second(3)

(c) The diagram shows part of the National Grid.

(i) Even though the householder uses solar cells to generate electricity for his home, the home stays connected to the National Grid.

Give one reason why the householder should stay connected to the National Grid.

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

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

(ii) The step-up transformer increases the efficiency of the National Grid.

Explain how.

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

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

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

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

(Total 10 marks)

Q29.The picture shows a washing machine. When the door is closed and the machine switched on, an electric motor rotates the drum and washing.

(a) Complete the following sentences.

(i) An electric motor is designed to transform electrical energy into

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

(ii) Some of the electrical energy supplied to the motor is wasted as

........................................ energy and ........................................ energy.(1)

(b) What happens to the energy wasted by the electric motor?

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

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

(c) The graph shows that washing clothes at a lower temperature uses less energy than washing them at a higher temperature. Using less energy will save money.

Temperature setting in °C

(i) Electricity costs 15p per kilowatt-hour (kWh).

The temperature setting is turned down from 40 °C to 30 °C.

Use the graph and equation in the box to calculate the money saved each wash cycle.

total cost = number of kilowatt-hours x cost per kilowatt-hour


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

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

Money saved = ...............................................(2)

(ii) Reducing the amount of energy used by washing machines could reduce the amount of carbon dioxide emitted into the atmosphere.

Explain why.

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

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

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

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

(Total 7 marks)

Q30.The picture shows a solar-powered aircraft. The aircraft has no pilot.

By NASA/Nick Galante [Public domain], via Wikimedia Commons

(a) Use words from the box to complete the following sentence.

electrical heat light sound

Solar cells are designed to transform ............................................................. energy

into ............................................................. energy.(2)

(b) On a summer day, 175 000 joules of energy are supplied to the aircraft’s solar cells every second. The useful energy transferred by the solar cells is 35 000 joules every second.

Use the equation in the box to calculate the efficiency of the solar cells.


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

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

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

(c) The aircraft propellers are driven by electric motors.

Give one environmental advantage of using electric motors to drive the aircraft propellers

rather than motors that burn a fuel.

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

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

(Total 5 marks)

Q31.The pictures show six different household appliances.

(a) Four of the appliances, including the fan heater, are designed to transform electrical energy into heat.

Name the other three appliances designed to transform electrical energy into heat.

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

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

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

(b) The bar chart shows the power of three electric kettles, X, Y and Z.

Kettle

(i) In one week, each kettle is used for a total of 30 minutes.

Which kettle costs the most to use?

Put a tick ( ) next to your answer.

X

Y

Y

(1)

(ii) A new ‘express boil’ kettle boils water faster than any other kettle.

Draw a fourth bar on the chart to show the possible power of an ‘express boil’ kettle.(1)

(c) The graph shows how the time to boil water in an electric kettle depends on the volume of water in the kettle.

Volume of water in litres

A householder always fills the electric kettle to the top, even when only enough boiling water for one small cup of coffee is wanted.

Explain how the householder is wasting money.

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

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

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

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

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

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

(Total 8 marks)

Q32.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?

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

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

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

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

(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.

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

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

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

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

(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.


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

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

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

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

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)

Q33.The Sankey diagrams show the energy transfers in a traditional coal-burning power station and a combined heat and power (CHP) station.

Waste energyWaste energy

(a) What effect does the waste energy from a power station have on the surroundings?

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

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

(b) Calculate the efficiency of the CHP station.


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

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

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

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

(c) Why is a CHP station more efficient than a traditional coal-burning power station?

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

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

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

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

(d) A CHP station is usually used to meet the demand for electricity within the local area. The electricity is not transmitted and distributed through the National Grid.

(i) What is the National Grid?

Tick ( ) one box.

A system of cables and pylons.

A system of cables and transformers.

A system of cables, transformers and power stations

(1)

(ii) Using the electricity locally and not transmitting it through the National Grid increases the overall efficiency of a CHP station by 7%.

Give one reason why.

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

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

(Total 7 marks)

Q34.A student finds some information about energy-saving light bulbs.

(a) The Sankey diagram is for a 30 W light bulb over a period of time.

(i) Calculate the energy wasted by the light bulb in this period of time.

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

Wasted energy = ................................. J(1)

(ii) What happens to the energy wasted by the light bulb?

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

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

(iii) Calculate the efficiency of this light bulb.

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

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

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

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

(iv) Calculate the period of time, in seconds, during which the 600 J is provided to the 30 W light bulb.

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

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

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

Time = ......................... s(2)

(b) A company that makes light bulbs provides information about some of their products.

The table shows some of this information.

Power in watts Lifetime in hours Cost of bulb in £

Filament bulb 60 1250 2.00

LED bulb 12 50 000 16.00

(i) Suggest why it is important to confirm this information independently.

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

(ii) A homeowner is thinking about replacing his filament bulbs with LED bulbs.

A 12 W LED bulb gives the same light output as a 60 W filament bulb.

Suggest reasons why the homeowner is likely to choose LED bulbs.

Use the information given in the table.

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

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

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

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

(iii) State one factor, other than efficiency, that is important when considering the choice of a bulb for lighting in the home.

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

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

(Total 10 marks)

M1. (a) generatoraccept dynamoaccept alternator

1

(b) (i) 1400ignore units

1

(ii) 0.3 or 30%any incorrect unit penalise 1 markallow 1 mark for the correct use of 600or 0.3% or 30

2

(c) 1 mark for each correct link

if more than 3 lines are drawn, mark only3 lines starting with those that are incorrect

3

(d) (i) 110no tolerance

1

(ii) 12no tolerance

1

(iii) wind speed may be too low to operate the generatoraccept wind may not always blowaccept power depends on wind speedaccept does not generate if wind speed is too highaccept does not generate if wind speed is above 12 (m/s)accept does not generate if wind speed is below 1.6 (m/s)accept it is unreliabledo not accept answers referring to cost only

1[10]

M2. (a) (i) heat1

(ii) temperature increases or (cause) convection (currents)accept gets warmeraccept gets hotter

1

(iii) 60% or 0.660 without % scores 1 mark0.6 with a unit scores 1 mark60 with incorrect unit scores1 mark

or correct substitution for 1 mark

2

(b) street1

more (energy transferred as) light or less (energy transferred as) heat or usefulenergy output the highest

can only score this mark if first mark scoredall efficiencies calculated correctly score 2nd mark point

1[6]

M3. (a) four calculations correctly shown200 × 10 – 1800 = £200100 × 10 – 2400 = –£140050 × 10 – 600 = –£10020 × 10 – 75 = 125accept four final answers only or obvious rejection of solar water heater and underfloor heating, with other two calculations completed any 1 complete calculation correctlyshown or showing each saving × 10 of all four calculations = 1 mark answers in terms of savings as a percentage of installation cost may score savings mark only

2

hot water boilercorrect answers only

1

(b) less electricity / energy to be generated / needed from power stationsaccept less demand

1

reduction in (fossil) fuels being burntaccept correctly named fuelaccept answer in terms of:fewer light bulbs required because they last longer (1 mark)less energy used / fuels burnt in production / transport etc. (1 mark)

ignore reference to CO2 or global warmingignore reference to conservation of energy

1[5]

M4. (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 around

1

(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]

M5. (a) kineticaccept movement

1

(b) (i) 3 (kWh)allow 1 mark for selecting the correct information

1

(ii) transfers more energyaccept transform or use for transferaccept electricity for energyallow higher (average) power and switched on for more time

2

(iii) any one from:

• use the internet

• brochures

• reading adverts

• visiting shops

• recommendation from friends / plumbers1

[5]

M6. (a) (i) £190nb mention idea of cost per J in £ will come to an approx figure full credit givenallow 1 mark for showing that the energy loss through the roof is ¼ of the total energy loss ie 150 / 600

2

(ii) £142.50allow ecf 50 % of their (a)(i) × 1.5 ie their (a)(i) × 0.75

1

(b) transferred to surroundings / atmosphere

or becomes spread out1

[4]

M7. (a) iron1

hairdryer1

kettle

answers can be in any order1

(b) sound1

(c) is more efficient than1

[5]

M8. (a) (i) makes it warmer / raises the temperatureaccept 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]

M9. (a) £15allow 1 mark for use of 125 (kWh)allow 1 mark for an answer 1500

allow both marks for 1500 pence / pallow 1 mark for correct calculation of annual cost for either freezer (£27 and £42)

2

(b) £45

or their (a) × 3allow 1 mark for correct use of 3allow 1 mark for 12 – 9 = 3

2

(c) any two from:the marks are for the explanation

yes plus explanation

• less electricity / energy needed / usedaccept less energy wasted

• less (fossil) fuels burnedaccept a named fossil fueldo not accept conserving (fossil) fuels

• less polluting gases emittedaccept a named polluting gas / greenhouse gases / carbon emissions / reduce global warmingaccept an answer in terms of nuclear fueleg less nuclear fuel required (1) less nuclear waste (1)

2

or no plus explanation

• old freezer must be disposed of

• hazardous chemicals inside freezeraccept CFC gases

• (lot of) energy used in producing new freezer[6]

M10. (a) (i) 0.6accept 60 %allow 1 mark for useful energy = 480answer 0.6 with any unit or 60 gains 1 mark only

2

(ii) transferred to surroundingsaccept goes into the airaccept heats the surroundings upaccept gets spread outaccept transferred into heat (only)do not accept wasted / lost unless qualifieddestroyed negates marktransferred into light / sound negates mark

1

(b) (i) 1.75allow 1 mark for converting to kWanswers of 0.7, 0.525, 0.35, 0.875, 1.05, 5.25 gains 1 markanswers of 1750 or 17.5 gains 1 mark

2

(ii) 21p or £0.21 or their (b)(i) × 121

(c) any two from:

• (more) electricity needs to be generated(more) electricity is being used

• (more) power stations needed

• (more) fossil fuels burntaccept named fossil fuel

• (more) pollutant gases emittedaccept named gasaccept harmful for pollutantaccept greenhouse gasesaccept atmospheric pollutionaccept answer in terms of any form of electricity generation and an associated environmental problem

2[8]

M11. (a) electrical1

soundcorrect order only

1

(b) the energy transformed by the TV will be destroyed1

(c) a higher efficiency than1

[4]

M12. (a) 9allow 1 mark for correct substitution(1.8 × 5)an answer of 9000 gains 1 markan answer of 2 or 15 gains 1 mark

2

(b) (3kW) fan heateraccept 3kWaccept the middle one

1

(c)features common to more than one heater, treat as neutral

oil-filled

low level heat

cannot be knocked over / space saving / no trailing wiresdo not accept just wall-mounted

or more control over heat outputdo not accept just 3 heat settings

1

fan

warms (office) rapidly or can be used to cool air (in summer)accept can be used as a fanaccept cool air fan (setting)accept ‘it has a cool air setting in case it gets too hot’do not accept a specific reference to cooling the heater

1

ceramic

can be switched on for set periods of timedo not accept just has a timer

or can be switched on before office is used / switched off automatically at night1

[6]

M13. (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]

M14. (a) light1

electricalcorrect order only

1

(b) (i) 0.2 or 1/5accept 20% for both marksallow 1 mark for correct substitution answer of 0.2%or 20 gains 1 markignore units

2

(ii) wastedaccept transformed to heat / other formsaccept transferred to the air / surroundings sound = neutral

1

(c) (i) any one from:

• can fly at nightaccept can fly when it is cloudyaccept as a back-up

• can stay in the air for longer

• can fly in the winter

• can fly fasterincreases power is neutral

1

(ii) any one from:

• produces no (pollutant) gases

or no greenhouse gasesaccept named gasaccept no air pollutiondo not accept no pollutionaccept less global warmingaccept harmful for pollutantaccept produces no carbondo not accept environmentally friendly

• produces no / less noise

• less demand for fuelsaccept any other sensible environmental advantage

1

(iii) accept any sensible suggestion eg, map the Earth’s surface / weather forecasting / spying / monitoring changes to the Earth’s atmosphere, etc

do not accept ideas in terms of transportingaccept use as a satellite

1[8]

M15. (a) 1.8 (p)these 4 marks can be broken down as follows:1 mark for correct transformation and substitution into efficiency equationie 0.8 × 1200 – useful powerPLUS1 mark for useful power = 960 W / 0.96 kWPLUS1 mark for waste energy transferred = 0.24 × 0.5orwaste energy transferred = 0.12 (kWh)

PLUS1 mark for cost = 0.12 × 15where a mathematical error has been made full credit should be given for subsequent correct method

4

(b) the waste energy is transferred as heat and sound1

to the surroundings where it spreads out / is shared bysurrounding particles

accept air for surroundings1

[6]

M16. (a) boiler1

generator1

(b) 0.3 or 30%allow 1 mark for substitution of 2 correct values taken from the Sankey diagram into correct equation

2

(c) decrease1

(d) any named biofuel eg wood, ethanol, straw1

(e) (nuclear) fission1

[7]

M17. (a) (i) 0.75allow 1 mark for correct transformation and substitutionie 0.15 = 5

2

(ii) 2accept 1.5 ÷ their (a)(i) correctly calculated

1

(b) any one from:

• seasonal changesaccept specific changes in conditionseg shorter hours of daylight in winter

• cloud coveraccept idea of changemust be stated or unambiguously impliedeg demand for water will not (always) match supply of solar energydo not accept figures are average on its owndo not accept solar panels are in the shade

1[4]

M18. (a) (i) kineticdo not accept movement

1

(ii) thermalaccept heat for thermal

sounddo not accept noise for soundboth answers required in either order

1

(b) transferred to surroundings / surrounding molecules / atmosphere‘it escapes’ is insufficient

orbecomes dissipated / spread out

accept warms the surroundingsaccept degraded / dilutedaccept a correct description forsurroundings eg to the washing machinedo not accept transformed into heat on its own

1

(c) a smaller proportion / percentage of the energy supplied is wastedowtteaccept a statement such as ‘less energy is wasted’ for 1 markdo not accept costs less to runignore references to uses less energy

2

(d) (i) 2.4 (p)accept 2 p if it is clear from the working out this is rounded from 2.4 pallow 1 mark for correct substitution of correct valuesie 0.2 × 12allow 1 mark for calculating cost at 40 °C (13.2 p)orcost at 30 °C (10.8 p)

2

(ii) any one from:

• less electricity neededignore answers in terms of the washing machine releasing less energyan answer in terms of the washing machine releasing CO2 negates the markdo not accept less energy is produced

• fewer power stations needed

• less fuel is burnedaccept a correctly named fueldo not accept less fuel is needed

1[8]

M19. (a) (i) 4allow 1 mark for correct transformation and substitution

ie substitution only scores if no subsequent steps are shown

2

(ii) diagram showing two output arrows with one arrow widerthan the other with the narrower arrow labelledelectrical / electricity / useful

1

(iii) any one from:

• time of day / year

• position of solar cells

• angle of solar cells (to the Sun)

• latitude

• cloud cover

• solar cells covered in dust / dirtaccept charger for solar cellsaccept any reasonable suggestion that would lead to a change in intensity of sun(light)the weather is insufficientdo not accept any physical changes to the charger eg area

1

causes a change in intensity of sun(light)accept brightness for intensityaccept a description of the reduction of intensity

1

(b) any one from:

• to check reliability / validity / accuracy

• to avoid bias1

(c) any two from:

• produce no / less (air) pollutionaccept named pollutantaccept produces no waste (gases)

• energy is freeaccept it is a free resourcedo not accept it is free

• (energy) is renewable

• conserves fossil fuel stocks

• can be used in remote areas

• do not need to connect to the National Grid2

[8]

M20. (a) heat / thermalor / andsound

do not accept noise

other forms of energy eg light negates answer1

(b) 0.4or40 %

allow 1 mark for orequivalent fractionan answer 0.4 % gains 1 markanswers 0.4 or 40 given with any unit gains 1 mark40 without % gains 1 mark

2[3]

M21. (a) (i) kineticaccept KEdo not accept movement

1

(ii) 0.75

allow 1 mark for correct substitution ie or75 %

an answer 0.75 % or 0.75 with a unit gains 1 mark onlyan answer 75 with or without a unit gains 1 mark only

2

(b) any one from:

• large areas of land are floodeduses large areas of land / takes up large areas of land is insufficient

• people's homes may be destroyed

• habitat (of animals and plants) lost / damagedconstruct is neutralvery noisy is neutral

1

(c) (i) system of cables and transformersboth required for the markaccept power lines / wires for cablesignore reference to pylons

inclusions of power stations / consumers negates answer1

(ii) less energy loss / wasted (in the cables)accept heat for energydo not accept no energy lossdo not accept electricity for energy

1

as the cables are shorter1

[7]

M22. (a) (i) 7.6allow 1 mark for correct substitution and / or transformation

ie 95 × 8.0

2

(ii) 25 (hours)allow 1 mark for obtaining number of kWh = 200an answer of 26(.3) gains both marks

2

(b) any two from

• transferred to the surroundings / air / atmosphere

• becomes spread out

• shared between (many) molecules

• (wasted as) heat / sound2

[6]

M23. (a) (i) 0.6or60%

allow 1 mark for correct substitution ie provided no subsequent step shownan answer of 0.6 / 60 with a unit gains 1 mark only

an answer of 60 gains 1 mark only2

(ii) heatallow thermal

1

(b) Kreason only scores if K is chosen

1

smallest amount of wasted energyreasons must be comparativeaccept waste arrow is narrowest

orlargest amount of useful energy

accept useful arrow is widestwaste arrow is smallest is insufficient

1

(c) 12 000 por£120

to score both marks the unit must be consistent with the numerical answeranswers 12 000 and 120 gain 1 mark onlyallow 1 mark for correct substitution ie 800 × 15 or 800 × 0.15provided no subsequent step shown

2[7]

M24. (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 jfor full credit the unit and numerical answer must be consistent

1[10]

M25. (a) fan1

drill1

washing machinefour circled including correct three scores 1 markfive circled scores zero

1

(b) Appliances only transfer part of the energy usefully1

The energy transferred by appliances makes the surroundings warmer1

[5]

M26. (a) (i)

1.6 (W)

allow 1 mark for correct substitution ie 2

(ii)

32 (%) / 0.32ortheir (a)(i) ÷ 5 correctly calculated

ignore any units1

(b) two output arrowsone arrow should be wider – judged by eye

1

narrower arrow labelled light or useful (energy / output / power)only scores if first mark awarded

and

wider arrow labelled waste (energy / output / power)accept heatignore numerical values

1

(c) (i) any two from:

• comparison over same period of time of relative numbers of bulbs

required eg over 50 000 hours 5 CFL’s required to 1 LEDaccept an LED lasts 5 times longer

• link number of bulbs to cost eg 5 CFL’s cheaper than 1 LEDan answer in terms of over a period of 50 000 hours CFLs cost £15.50 (to buy), LED costs £29.85 (to buy) so CFLs are cheaper scores both marksan answer in terms of the cost per hour (of lifetime) being cheaper for CFL scores 1 mark if then correctly calculated scores both marks

• over the same period of time LEDs cost less to operate (than CFLs)2

(ii) any one from:

• price of LED bulbs will dropdo not accept they become cheaper

• less electricity needs to be generatedaccept we will use less electricity

• less CO2 produced

• fewer chips needed (for each LED bulb)

• fewer bulbs required (for same brightness / light)

• less energy wasteddo not accept electricity for energy

1[8]

M27. (a) (i) light (energy)this answer only

1

(ii) raises its temperatureaccept warms / heats itaccept air molecules / particles gain energy / move fasterdo not accept heatdo not accept pollution

1

(iii)

20% or 0.2

allow 1 mark for correct substitution ie provided that no subsequent step is shown20 without % scores 1 mark, 20 or 0.2 with a unit scores 1 mark

2

(iv) mercury can be recovered /reused / recycledormercury (vapour) does not get into the atmosphere / environment / air

accept to stop mercury poisoning the land / getting into the food chain / water supplyaccept poisonous gas for mercury (vapour)do not accept general poisoningcause harm to the environment is insufficient

1

(b) a smaller1

(c) reaches full brightness fasteraccept brighter / switches on faster accept it does not get as hotaccept it will not burn someone who touches itaccept stays coolaccept temperature does not increase as muchaccept temperature only goes to 24 (°C)accept contains no mercurydo not accept wastes less energy

1

(d) top two boxes both ticked

The number of hours each bulb lasts before needing to be replaced.

The power of each bulb in watts.1

[8]

M28.(a) (i) replaced faster than it is usedaccept replaced as quick as it is usedaccept it will never run out do not accept can be used again

1

(ii) any two from:two sources required for the mark

• wind

• waves

• tides• fall of water

do not accept water / oceansaccept hydroelectric

• biofuelaccept a named biofuel eg wood

• geothermal1

(b) (i) any two from:

• increases from 20° to 30°

• reaches maximum value at 30°

• then decreases from 30°

• same pattern for each monthaccept peaks at 30° for both marksaccept goes up then down for 1 mark ignore it’s always the lowest at 50°

2

(ii) 648an answer of 129.6 gains 2 marksallow 1 mark for using 720 value only from table allow 2 marks for answers 639, 612, 576, 618(.75) allow 1 mark for answers 127.8, 122.4, 115.2, 123.75

3

(c) (i) (sometimes) electricity demand may be greater than supply (of electricity from the system)

accept cloudy weather, night time affects supply

or

can sell (excess) electricity (to the National Grid)1

(ii) decreases the currentaccept increases the voltage

1

reducing energy loss (along cables)accept less heat / thermal energy lost / produced

1[10]

M29.(a) (i) kineticdo not accept movement

1

(ii) thermal soundaccept heat for thermal do not accept noise for soundboth answers required in either order

1

(b) transferred to surroundings / surrounding molecules / atmosphere‘it escapes’ is insufficient

orbecomes dissipated / spread out

accept warms the surroundingsaccept degraded / dilutedaccept a correct description for surroundings eg to the washing machinedo not accept transformed into heat on its own

1

(c) (i) 3 (.0 p)allow 1 mark for correct substitution of correct values ie 0.2 x 15allow 1 mark for calculating cost at 40°C (16.5p)orcost at 30°C (13.5p)

2

(ii) any two from:

• less electricity neededignore answers in terms of the washing machine releasing less energy an answer in terms of the washing machine releasing CO2 negates mark do not accept less energy is produced

• fewer power stations needed

• less fuel is burnedaccept a correctly named fuel do not accept less fuel is needed

2[7]

M30.(a) lightcorrect order only

1

electrical

1

(b) 0.2 or 1/5accept 20% for both marks

allow 1 mark for correct substitution ie answers of 0.2% or 20 gain 1 mark only

2

(c) any one from:

• produces no (pollutant) gasesorno greenhouse gases

accept named gasaccept no air pollution do not accept no pollutionaccept less global warmingaccept harmful for pollutantaccept produces no carbon do not accept environmentally friendly

• produces no / less noise

• less demand for fuelsaccept any other sensible environmental advantage

1[5]

M31.(a) iron1

hairdryer1

kettle1

answers can be in any order

(b) (i) Y1

(ii) bar drawn with any height greater than Yignore width of bar

1

(c) (bigger volume) takes more time (to boil)accept explanation using data from graph

1

(so) more energy transferreddo not accept electricity for energy

1

(and) this costs more moneyignore reference to cost of waterwasting more money because heating more water than needed is insufficient

1[8]

M32.(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]

M33.(a) warms itdo not accept answers in terms of waste gases or pollution

1

(b) 80% or 0.8answers of 80 or 0.8 plus a unit gain 1 mark only

or allow 1 mark for a correct substitution, ie an answer of 35% or 0.35 gains 1 markanswers of 85%, 75%, 0.85 or0.75 gain 1 mark

2

(c) some of the energy that would be wasted (by a coal-burning power station)accept less waste energy

1

is usefully used (to heat homes etc)accept energy used to heat homes etc

1

(d) (i) A system of cables and transformers1

(ii) less energy / power loss / wasted (in shorter cables)accept no energy / power loss / wasted (in shorter cables)accept energy is lost when transmitted through cablesdo not accept electricity for energy

1[7]

M34.(a) (i) 1501

(ii) transferred to the surroundings by heatingreference to sound negates mark

1

(iii) 0.75450 / 600 gains 1 markaccept 75% for 2 marksmaximum of 1 mark awarded if a unit is given

2

(iv) 20 (s)correct answer with or without working gains 2 markscorrect substitution of 600 / 30 gains 1 mark

2

(b) (i) to avoid bias1

(ii) use less power and last longer1

1 LED costs £16, 40 filament bulbs cost £80

or

filament costs (5 times) more in energy consumption1

(iii) any one from:

• availability of bulbs• colour output• temperature of bulb surface

1[10]

E1. Parts (a) and (b)(i) were well answered.

(ii) Many candidates inverted the figures before calculation or gave a unit to their final numerical answer.

(c) The noise problem of wind was usually given correctly but many candidates transposed the problems of hydro-electricity and tides.

(d) Most candidates identified the maximum power from the graph but many went on to state that the generator stopped working at 8 m/s because the graph line became horizontal at that point. The unreliability of wind generators was widely known.

E2. Many candidates excellently completed this question. Efficiency can be a difficult concept but the format of the question allowed candidates to demonstrate their understanding.

(a) In part (iii) the main errors involved either 400 being used as the total energy supplied or the correct numerical answer being offered but with the unit J added.

(b) Only a few candidates lost one of the marks by not making their answer comparative.

E3. In part (a) those candidates who chose the payback route generally gained no credit, unless they picked the boiler as the best option. Many candidates scored two marks for selecting the

boiler and a correct calculation. A significant number of candidates scored all three marks for completing all the calculations correctly and making the correct choice.

Few candidates scored 2 marks in part (b). Most candidates failed to link the less energy back to the power station. The common mark scored was for stating the reduction in fuel burnt. Many considered the efficiency of the bulbs; but did not link it back to the need to generate less electricity. Very few thought about the need for fewer bulbs and the energy saving in their manufacture. There were a significant minority of candidates who thought that conventional light bulbs emit carbon dioxide or that energy loss somehow produces carbon dioxide, often as a result of heat loss.

E4. 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”.

E5. In part (a) the vast majority of the candidates showed an understanding of energy transfer and many successfully achieved maximum marks for the calculation in part (b)(i). However, the cost implications of using different power cycles for the washing machine were not widely understood and many candidates were unable to describe how they would undertake research to compare the energy efficiency of domestic appliances. The candidates that were successful generally stated using the Internet.

E6. (a) (i) Whilst quite a lot of candidates were able to work out that 25 % of the energy was lost through the roof, many failed to realise that they needed to work out 25 % of the cost.

(ii) This calculation proved rather difficult for many candidates.

Overall in part (a) there were a surprisingly large number of minor arithmetical errors and several answers which candidates should have recognised as unrealistically small or large eg in part (ii) answers such as £1 or £200,000.

(b) Candidates scored well with most gaining credit.

E7. (a) Most candidates could correctly name the other three appliances designed to transform electrical energy into heat. A few included the fan heater amongst their choices which was given in the question and a very small number wrote down the names of appliances that were not shown in the pictures.

(b) Most candidates correctly chose sound energy as being the form in which the fan heater wasted energy. A few however selected heat, perhaps thinking that this is always the answer to a ‘wasted energy’ question.

(c) The majority of candidates correctly identified that fan heater L was more efficient than fan heater M.

E8. (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.

E9. (a) Most candidates knew how to answer this, but a significant number failed to realise that their answer of ‘1500’ was pence, not pounds.

(b) This proved to be a difficult question for many candidates, a significant number not attempting it. Of those who made an attempt, quite a few realised that there was a saving of 3 years, but did not link the pay-back time to their previous answer.

(c) Most candidates opted for the ‘yes’ answer, gaining some credit for stating that less electricity would be used by the new freezer, but often failing to describe how this would

benefit the environment. Of those who chose the ‘no’ option some credit was usually gained for the ideas that the appliance would need to be disposed of.

E10. (a) (i) This calculation was correctly done by most candidates. Of those who did not score full marks, some gained credit for calculating the useful energy as 480 J, but were then unable to complete the calculation correctly. Others arrived at the correct numerical answer, but added an incorrect unit such as J or J/s.

(ii) A wide range of responses was seen. A number of answers had the energy changing into light/sound and therefore being used by the person watching the television. There were indications that many candidates had not read the question carefully enough to appreciate that it referred to the ‘useful’ energy and what happens to it ‘eventually’.

(b) (i) Just under half of the candidates gained full marks. The most common incorrect answer was 1750 showing no conversion from watts to kilowatts. Many candidates did not read the question carefully and instead of referring to the compact stereo, chose another item or all of the items together.

(ii) The candidates that answered correctly in part (b)(i) generally scored this mark. Many candidates scored the mark for error carried forward mostly from an answer of 1750. A significant but small number of candidates made errors on converting pence to pounds or multiplied by 0.12 but forgot to put in £ sign. Some candidates who had failed to do the correct conversion in part (b)(i) arrived at a cost of £210 for leaving a small electrical item on standby for about a week!

(c) This was very well answered by many candidates. A common mistake seen was that the electrical appliance itself was giving off heat, which contributed to global warming, or more bizarrely, was giving off carbon dioxide.

E11. (a) The vast majority of candidates knew that a television is designed to transform electrical energy into light and sound energy.

(b) Most candidates could identify the false statement from the list.

(c) Most candidates realised that wasting less energy leads to a higher efficiency.

E12. Foundation Tier

(a) Most candidates could substitute the correct numbers into the equation, although some erroneously put in a figure of 8 hours instead of 5. The most common mistake was to fail to convert 1800 watts into 1.8 kilowatts, thus arriving at an answer of 9000 instead of 9.

(b) Many candidates chose the ceramic heater, perhaps because it appeared to have the largest number attached to it.

(c) Most candidates were able to score at least one mark on this question, although very few scored all three marks. The most common mistake was simply to pick a feature from the illustration and copy it down. These candidates failed to realise that (i) it should be a feature not possessed by either of the other two, and (ii) that they should explain why this feature is an advantage.

Higher Tier

(a) A large number of candidates scored at least 1 of the 2 marks, common mistakes were a failure to convert from W to kW, or wrongly converting by dividing by 100. A surprising number of answers used the time as 8 hours, presumably because of the 8-hour timer. It would appear that many candidates do not read the questions thoroughly.

(b) This was well answered on the whole, although it appeared that some candidates just looked for the highest number, regardless of units.

(c) Many marks were lost by candidates not comparing each heater with the other two, again an example of not reading the question thoroughly. Good answers explained why the feature would be an advantage rather than just picking out a statement from the lists given.

E13. 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.

E14. (a) Most candidates correctly stated that solar cells are designed to transform light energy into electrical energy. The most common mistake was to state that they transform heat energy into electrical energy.

(b) (i) The majority of candidates could substitute the correct numbers into the correct places in the equation. However, some candidates then found that they could not cope with a fraction where the denominator was larger than the numerator; they therefore inverted the fraction and ended up with the answer 5 instead of 0.2. It is possible that some candidates did not use a calculator in the examination.

Some candidates tried, unnecessarily, to express the answer as a percentage. Those who correctly answered 20% gained both marks; those who erroneously stated it to be 0.2% were only awarded one mark.

(ii) Most candidates correctly stated that the energy that is not usefully transferred is wasted.

(c) (i) Most candidates correctly stated that either the fuel cells were to act as a backup for the solar cells, or that this enabled the aircraft to fly at night or when there was insufficient light.

(ii) Most candidates were able to state that burning fuels releases gases such as carbon dioxide into the atmosphere. Candidates whose answers were very vague such as “it reduces pollution” were not awarded a mark.

(iii) Many candidates believed that such an aircraft would be able to fly into space or be used to visit the moon. Another common mistake was to misread the question and instead of suggesting a possible use for the aircraft, some candidates were giving an advantage of this aircraft over conventional passenger jets.

E17. (a) (i) This was the best answered numerical question with many candidates able to transform the equation and substitute values to arrive at the correct answer.

(ii) This proved difficult for the majority of candidates, even with the correct answer to the previous part.

(b) Very few correct answers were seen, the majority being too imprecise and not giving a reason for the variation in sunlight.

E18. (a) (i) Kinetic energy was correctly identified by most candidates.

(ii) Most candidates correctly stated that sound and thermal / heat were the two forms of wasted energy.

(b) This was poorly answered, with only just over a quarter of candidates realising that the energy was transferred to the surroundings.

(c) Most candidates were able to earn 1 mark here for stating that the more efficient machine would waste less energy. Very few candidates answered in terms of the proportion of the input energy that was wasted was less.

(d) (i) Few candidates were able to score both marks here. Many of the weaker candidates had difficulty in placing the decimal point correctly. Another common mistake was to calculate the cost for either 40 °C or for 30 °C, but not work out the difference.

(ii) Few correct answers. Many candidates thought that washing machines produced carbon dioxide directly.

E19. (a) (i) Less than half of the candidates answered this correctly. Many were unable to transpose the equation correctly.

(ii) Only about a third of candidates were able to draw something resembling a Sankey diagram and label it appropriately. Whilst the majority of candidates obviously had some idea that a Sankey diagram had some arrows going in different directions, some drew a picture of solar cells, and over a tenth did not attempt the question.

(iii) This was answered reasonably well, with over three quarters of candidates gaining at least one of the two marks, usually for realising that a change in intensity of the sunlight would affect the time taken to charge the battery. However, less than half of these went on to score the second mark by giving a factor which would change the intensity.

(b) This question was correctly answered by the majority of candidates. However, many seem to have a dim view of company scientists, indicating that they would lie or falsify results.

(c) Nearly all candidates gained at least one mark, with more than half scoring both. The most common answers were that the Sun is a renewable resource and that solar cells do not produce pollutant gases.

E20. (a) Just under a half of the candidates wrote a correct response of either heat (thermal) or sound energy as the form of wasted energy. However, many candidates opted for kinetic or electrical energy.A few candidates read the word ‘as’ to mean ‘because’ and wrote a sentence in the gap to try to explain why energy is wasted.

(b) There was a pleasing response to this question, with about half of the candidates obtaining the correct answer to the calculation. The most common mistake was to invert the fraction and hence arrive at an answer of 2.5 rather than 0.4.

E21. (a) (i) This was well answered.

(ii) The majority of candidates were able to substitute correctly into the given equation.

Mistakes made subsequently were to do the arithmetic incorrectly, or to give a wrong unit with a correct numerical answer, eg 75 J or 0.75 %.

(b) Few candidates scored this mark. A common insufficient answer was to say that it would take up a lot of land, without going on to explain the consequences. Few candidates seemed to realise that scaling up by a factor of 100 000 would require the area to be flooded.

(c) (i) As a simple recall of knowledge question it was surprising that very few candidates were able to give the correct answer. Common misconceptions included the idea

that pylons carry the electricity; that the power station or consumer is part of the National Grid.

(ii) Despite the given information stating that the electricity from the micro-system was transferred to local homes via a transformer, a large number of answers stated that no transformers would be needed, indicating that many candidates had failed to read the question carefully.

E22. (a) (i) The vast majority of students attempted this calculation, with over three quarters getting the correct answer. The most common errors were in transposing the equation incorrectly, or including the water temperature of 60°C in the calculation.

(ii) Around half of the students were able to use the total cost of £30 and the cost per kWh of 15p to calculate a figure of 200; however that is the point at which most stopped, quoting an answer of 200 hours. A few then attempted to involve the power, with only a minority ending up with the correct answer. A few students did not attempt to answer this question.

(b) Most students gave at least one correct point in answer to this question, with around half being able to give two points correctly.

E23. (a) (i) There were many correct answers here. Use of ‘J’ as a unit for the answer was the most common error.

(ii) Most students correctly identified ‘heat’ as the wasted energy.

(b) Most students correctly gave ‘K’ as the most efficient TV. Of those students, nearly three quarters then went on to supply a correct reason for their choice. Students who simply quoted values from the Sankey diagrams and attempted no comparison did not score the second mark.

(c) Most students were able to multiply the number of kWh by the cost per kWh to get 120 or 12 000. However less than a half of those students were able to give the appropriate unit to match their numerical answer.

E24. (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.

E25. (a) Surprisingly, less than two-thirds of students could identify the fan, the drill and the washing machine as being the devices that were designed to transfer electrical energy to kinetic energy.

(b) Just over half of students scored both marks, and just under half scored one mark.

E26. (a) (i) Almost a half of students gained both marks. The common errors were to multiply 8 by 20 without then dividing by 100 or divide 20 by 8 giving an answer of 2.5.

(ii) A significant number of students thought this question could not be answered due to lack of data. These students had failed to read the question stem that told them both bulbs had the same useful power output. Students scoring both marks in part (a)(i) usually also scored this mark. However, there were a significant number of students giving answers in excess of 100 %.

(b) Students presented numerous versions of a Sankey diagram. Some students failed to label the two outputs and so limited themselves to one mark. A number of students gave

three output arrows. Students would be well advised to spend some time practising drawing neat, labelled diagrams.

(c) (i) Students were asked to use the data and not simply to repeat it. However, there were many good answers that compared the cost over the same period of time and gained both marks. Different, but still valid answers, which used correct calculations in terms of cost per hour or hours per pound spent, were regularly seen.

(ii) There was a wide variety of answers, many unfortunately, too vague to credit. The most popular correct answer was in terms of ‘waste less energy’.

E27. (a) (i) Only about half of the students realised that the question required them to name a type of energy, ie light. Many students wrote ‘4 joules’.

(ii) Fewer than half of the students realised that the waste energy would warm the air. Many said that the waste energy would cause pollution.

(iii) About one-third of the students obtained the correct answer of 20 % or 0.2. Some students only scored one mark, either because the failed to show the percentage sign after the number 20, or because they added a unit after the number. Many students showed the correct substitution but could not then correctly complete the arithmetic.

(iv) This was a poor scoring question, mainly because of the very vague nature of most of the answers. Many students simply repeated the information in the question and stated that mercury is poisonous. Others used phrases such as ‘foxes could eat them’.

(b) Most students realised that the LED bulbs would waste a smaller proportion of the input energy.

(c) Some students misread the graph, and thought that the CFL would be brighter than the LED. Others ignored the part of the question that stated ‘Apart from a higher efficiency’ and talked about energy losses. However, about half of the students gave a correct response.

(d) The most common mistake in this question was the failure to spot the requirement that two boxes should be ticked.

E28.(a) (i) Around half of the responses scored the mark for this question. A common errors was to indicate that the energy source could be used again.

(ii) Three-quarters of students gave two correct responses.

(b) (i) Students found difficulty in analysing the data to find any patterns. Around half were able to identify that an angle of 30° led to the maximum average energy input. A large number of students saw the word ‘average’ and attempted to calculate the average of the values given for each month. A surprisingly high number of responses seemed to think that the ‘degrees’ referred to the temperature.

(ii) A minority of students gained all three marks for this calculation, but more were able to gain one mark by correctly identifying the value of 720 J/s.

(c) (i) Around two-thirds of students were able to give a coherent and correct answer.

(ii) Less than one-fifth of responses gained both marks, slightly more students were able to gain one mark, usually for indicating that less energy would be lost. ‘Absolute’ statements such as ‘no energy would be lost’ were often seen.

E29.(a) (i) Nearly all students responded correctly with ‘kinetic’ energy.

(ii) The majority of answers correctly identified the two forms of wasted energy.

(b) Just over half of responses gained credit. Insufficient responses included ‘it is wasted’ (given in the question) or ‘it turns into heat’ (answered in the previous part).

(c) (i) Fewer than half of the students gained both marks for this question, although some were able to gain one mark for calculating the cost at 40°C or 30°C.

(ii) More than half of the responses failed to gain credit, many answers indicating that the washing machine itself gave off carbon dioxide. Of those students who had the correct idea, many failed to answer the question as to why reducing the amount of energy used reduces the amount of carbon dioxide.

E30.(a) A majority of students were able to answer this question correctly. Nearly every response indicated that the student realised that the end product of this energy transformation would be 'electrical', but some thought that it was the Sun's 'heat' that was transformed.

(b) A good proportion managed the calculation and scored both marks. A minority used the data the wrong way round and got '5' as the efficiency. Some students were penalised for missing the percentage sign when it was appropriate or for adding spurious units to their answer.

(c) Many students realised that using electric motors meant no release of polluting or harmful gases into the atmosphere. However, it must be emphasised again that vague terms like 'environmentally friendly' or 'eco friendly' will not gain any credit. A small proportion of answers indicated that some thought electric motors were powered by wind energy rather than solar.

E31.(a) A straightforward question that allowed many students to gain all 3 marks available. Some did choose 'fan heater', even after they were told in the question stem to 'name theother three appliances designed to transform electrical energy into heat'. A small minority named devices that were not on the list provided.

(b) (i) The vast majority of students were able to identify Y as the costliest kettle.

(ii) Most students were able to draw an acceptable bar on the chart, gaining the mark.

(c) Most students were able to gain some credit for their answer and there were some very good and clear responses that scored full marks. Many realised that it would take longer to boil the water if the kettle was filled and then they went on to suggest that it would cost the householder more money. The third marking point, that more energy would be used, was seen less often. The use of 'electricity' rather than 'energy' meant that some students did not gain this mark.

E32.(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.

E33.(a) Very few students appreciated that the waste energy from the power station would cause an increase in temperature of the surroundings. Of those who were thinking along these lines they often stated that the waste energy from the power station would cause global warming. Many students thought that the waste would be in the form of gases and were therefore talking about pollution of the environment.

(b) The best students were able to correctly calculate the efficiency of the CHP station. However, some of these failed to gain maximum marks because either they neglected to insert the % sign after the number 80 or they quoted the efficiency as 0.8 but then put a % sign or a unit after the number.

(c) About half of the students gained one of the two marks on this question.

(d) (i) Very few students knew that the National Grid comprises cables and transformers; the majority thought that it comprised cables and pylons.

(ii) Few students could provide an adequate reason for the increased efficiency. Responses such as “the electricity doesn't have to travel far”, “it's quicker/cheaper” and the use of “electricity” rather than “energy” meant that many scored no marks.

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