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P1 04 Heating and Insulating Buildings

212 minutes

212 marks

Q1. The diagram shows a side view of a double-glazed window.

(a) Use each of the terms in the box to explain how heat is lost from inside a house through the window.

conduction convection radiation

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(b) Besides heat, state one other form of energy that passes through double-glazed windows.

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(c) Explain why plastic foam cavity wall insulation cuts down energy transfer between warm inner walls and cooler outer walls.

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(d) When it rains the walls and windows of a house get wet.

Explain how the drying process can increase the cooling of the house.

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(Total 8 marks)

Q2. People do a number of things to reduce the energy loss from their homes.

(a) Describe one thing they may do to cut down the energy loss through:

(i) the roof;

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(ii) the outside walls;

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(iii) the glass in the windows;

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(iv) gaps around the front and back doors.

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(b) A house is more difficult to keep warm in cold weather. What other type of weather makes it difficult to keep a house warm?

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(Total 5 marks)

Q3. The drawing shows parts of a house where it is possible to reduce the amount of energy lost.

(a) Give one way in which the amount of energy lost can be reduced from each of the following parts of the house.

1, 2 and 4 ....................................................................................................................

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(b) Energy consumption can be reduced by using a more efficient boiler or more efficient light

bulbs.

What is meant by a more efficient light bulb?

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(Total 4 marks)

Q4. The table gives information about some methods of conserving energy in a house.

Conservation method Installation costin £

Annual saving onenergy bills in £

Cavity wall insulation 500 60

Hot water tank jacket 10 15

Loft insulation 110 60

Thermostatic radiator valves

75 20

(a) Explain which of the methods in the table is the most cost effective way of saving energy over a 10 year period. To obtain full marks you must support your answer with calculations.

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(b) Describe what happens to the energy which is 'wasted' in a house.

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(Total 5 marks)

Q5. The diagram below shows a house which has not been insulated. The cost of the energy lost from different parts of the house during one year is shown on the diagram.

(a) The total cost of the energy lost during one year is £1000.

(i) What is the cost of the energy lost through the floor?

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(ii) Suggest one way of reducing this loss.

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(b) The table below shows how some parts of the house may be insulated to reduce energy losses. The cost of each method of insulation is also given.

WHERE LOST COST OF ENERGYLOST PER YEAR (£)

METOD OFINSULATION

COST OFINSULATION (£)

roof 250 fibre-glass in loft 300

walls 350 foam filled cavity 800

windows 100 double glazing 4500

doors 150 draught proofing 5

(i) Which method of insulation would you install first? Explain why.

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(ii) Which method of insulation would you install last? Explain why.

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(Total 9 marks)

Q6. (a) The diagram shows a hot water system.

(i) Explain why the boiler is below the hot water tank.

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(ii) Why is heat energy transferred from hot water in the tank to the surrounding air?

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(iii) Name the process by which energy is transferred through the sides of the tank.

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(iv) How may heat loss from the hot water tank be reduced?

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(b) One way of reducing heat loss from a house is by cavity wall insulation. Foam is pumped between the inner and outer brick walls as shown in the diagram.

How is heat loss from a house reduced by:

(i) having a cavity wall?

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(ii) filling the cavity with foam?

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(Total 9 marks)

Q7. (a) The diagram shows hot water being poured into a mug.

(i) Complete the sentence by choosing the correct words from the box. Each word may be used once or not at all.

air mug table water

Heat energy is being transferred from the ...................................................... to

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

(ii) When will this transfer of heat energy stop?

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(b) In the box are the names of four types of fuel used to heat homes.

coal gas oil wood

Which one of these types of fuel is renewable?

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(c) The diagram shows where heat energy is lost from a house.

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

conduction conductor convection electric evaporation insulator

The amount of heat energy lost through the windows by

....................................................... can be reduced by using thick curtains. The

curtains trap a layer of air and air is a good ................................................... .

The curtains will also stop .................................................... currents pulling

cold air into the room through small gaps in the window.(3)

(ii) Write down one other way of reducing heat loss from a house.

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(Total 7 marks)

Q8. (a) The diagram shows an immersion heater used to heat water inside a tank. Heat is transferred through the water by convection.

(i) Draw arrows on the diagram to show the movement of the water in the tank when the heating element is switched on.

(2)

(ii) Explain how a convection current is set up in the water. The explanation has been started for you.

When the heating element is switched on, the hot water nearest the element rises

because ...........................................................................................................

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(b) The diagram shows two ways to reduce heat loss through the walls of a house.

(i) How is the aluminium foil able to reduce heat loss?

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(ii) The plastic foam is good at reducing heat loss through the walls. Explain why.

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(c) Evaporation is an important heat transfer process. When sweat evaporates, it takes heat energy from your body. As humidity increases, you are more likely to feel hot and uncomfortable. Explain why.

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(Total 10 marks)

Q9. (a) The diagram shows the ways in which heat energy can be transferred from an old house.

(i) Calculate the percentage of energy transferred by draughts.

% energy transferred by draughts = ......................................(1)

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

conduction convection radiation

Draughts transfer heat energy by ......................................................................(1)

(iii) State one way of reducing the heat transfer by draughts.

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(b) The diagram shows a section through the walls of a house built in 1930.

Explain how the air cavity between the two walls reduces the heat transfer from the house.

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(c) The table shows the installation costs and yearly savings on energy bills for different methods of insulating a house.

Method of insulation

Installation cost in £

Yearly saving on energy bills in £

Double glazing 4000 65

Loft insulation 240 60


(i) Give one reason why loft insulation is often fitted to an old house before double glazing or cavity wall insulation.

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(ii) The time it takes for the saving on energy bills to equal the cost of installing the insulation is called the pay-back time.

Calculate the pay-back time for loft insulation.

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Pay-back time = .................................................... years(1)

(Total 7 marks)

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

Method of reducing energyconsumption

Installation cost in £

Annual saving on 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.

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(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.

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(Total 5 marks)

Q11. (a) The graph shows the temperature inside a flat between 5 pm and 9 pm. The central heating was on at 5 pm.

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

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

What time do you think the curtains were closed?

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Give a reason for your answer.

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

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

conduction conductor convection evaporation insulator radiation

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

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

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

Type of insulation Cost toinstall

Money save eachyear on heating

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.

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

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(Total 9 marks)

Q12. (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.

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(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?

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

(b) What happens to the wasted energy?

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(Total 4 marks)

Q13. The diagrams show the cross-section of three double glazed windows.

The gap between the two sheets of glass can be filled with either air or a mixture of air and argon.

The U-values for different types of double glazed windows, using different types of glass X and Y, are given in the table.

Type of window 12 mm gap

16 mm gap

20 mm gap

1 Glass type X with air 2.9 2.7 2.8

2 Glass type X with air and argon 2.7 2.6 2.6

3 Glass type Y with air 1.9 1.8 1.8

4 Glass type Y with air and argon 1.6 1.5 1.5

(a) Which type of window, 1, 2, 3 or 4 is the least energy efficient?

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(b) Which two windows should be compared to decide if adding argon to the gap improves the energy efficiency of the window?

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(c) A householder is going to buy new windows. The sales assistant recommends that the householder buys windows with a 20 mm gap. These windows are much more expensive than those with a 16 mm gap.

It is not worth the householder paying the extra cost to buy 20 mm windows rather than 16 mm windows.

Explain this in terms of energy efficiency.

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(d) Windows are given an energy rating, from A down to G. The diagram shows the energy label from one type of double glazed window.

All new double glazed windows must have an energy rating of C or above.Windows having a C rating have a U-value of 1.9.

Which windows given in the table would the householder be unable to buy?

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(e) Glass transmits infrared radiation and visible light. The amount transmitted depends on the type and thickness of the glass. The data from tests on two different types of glass is

displayed in the graph below.

A homeowner has a glass conservatory built on the back of the house. The homeowner tells the builder that the inside of the conservatory should stay as cool as possible throughout the summer.

Explain why the builder uses ‘Type B’ glass for the conservatory.

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(Total 7 marks)

Q14. The diagram shows where heat is lost from a house that is not insulated.

(a) (i) Through which part of the house is most heat lost?

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(ii) How can the heat loss through the windows be reduced?

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(b) A homeowner wants to reduce her energy bills and make her home more energy efficient. The table shows five ways this could be done. The table also shows how much money each way would save the homeowner each year.

Cost Money savedeach year

Installing loft insulation £175 £60

Fitting draught-proofing £45 £20

Installing cavity wall insulation £300 £80

Adding a hot water tank jacket £15 £20

Using energy efficient light bulbs £60 £30

(i) Which one of the five ways of reducing energy bills would reduce the yearly energy bill the most?

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(ii) This year the homeowner has only got £60 to spend to improve the energy efficiency of her home.

Use the information in the table to explain what the homeowner should spend this money on.

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(Total 5 marks)

Q15. (a) The diagram shows two switches on a room heater. The heater has three power settings. The power produced by two of the settings is given in the table.

Setting Power in kW

Low 0.5

Medium 1.5

High

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

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

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Power = ......................................................... kW(1)

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

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

energy transferred(kilowatt-hour, kWh)

= power(kilowatt, kW) × time

(hour, h)


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

(iii) Electricity costs 12 pence per kilowatt-hour.

Use the equation in the box to calculate how much the heater costs to use onmedium power for three hours.

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


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Total cost = ................................................ pence(2)

(b) The heater is used to warm a room.

The graph shows how the temperature of the room changes from the moment the heater is switched on.

The heater was first used on the medium setting.

(i) At what time was the heater setting changed to the high setting?

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(ii) From 7 pm until 10 pm, the temperature of the room is not changing.

Which one of the following statements gives the reason why the temperature of the room is not changing?

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

The room is losing energy slower than the heater supplies energy.

The room is losing energy as fast as the heater supplies energy.

The room is losing energy faster than the heater supplies energy.

(1)(Total 8 marks)

Q16. Glass reflects, absorbs and transmits both infra red radiation and visible light.

(a) The diagram shows the percentages of visible light that are reflected and absorbed by one type of glass.

What percentage of visible light is transmitted by this type of glass?

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

(b) The amounts of infra red radiation and visible light transmitted by glass depend on the type and thickness of glass. The data obtained from tests on two different types of glass is displayed in the graph below.

(i) To be able to compare the two types of glass, it was important to control one variable.

What variable was controlled in the tests?

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(ii) A homeowner has a glass conservatory built on the back of the house. The homeowner tells the builder that the inside of the conservatory should stay as cool as possible throughout the summer.

Explain why the builder uses ‘type B’ glass for the conservatory.

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(c) Infra red and visible light can be used to send signals along an optical fibre.

Which one of the following diagrams, X, Y or Z, shows the path taken by a signal as it travels along an optical fibre?

Draw a ring around the correct diagram.

(1)(Total 5 marks)

Q17.(a) The table gives information about some ways of reducing the energy consumption in a house.

Method of reducing energyconsumption

Installationcost in £

Annual saving onenergy bills in £


Jacket for hot water tank 12 35

Upgraded central heating controls 310 80

Show that over 5 years, the most cost-effective method of reducing energy consumption is to install cavity wall insulation.

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(b) Any device that transforms energy will waste energy.

Why must the total energy input to such a device always equal the total energy output from the device?

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(c) A holiday cottage has a pre-payment electricity meter. The electricity is charged at the rate of 20 p per kWh. A £2 coin is put into the meter and a 2.5 kW fire switched on.

Use the equations in the box to work out how many hours it will be before £2 runs out.Assume that no other electrical device is switched on.

energy transferred = power × time

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


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Time = ................................... hours(2)

(Total 5 marks)

Q18. Warm air inside a house contains water in the form of a gas. The water condenses onto cold surfaces such as windows. This leaves liquid water on the inside of the glass.

(a) Explain what happens to the particles when water changes from a gas to a liquid.

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(b) Many houses in the UK have double-glazed windows.

Photograph supplied by iStockphoto/Thinkstock

If the window is double-glazed rather than single-glazed there is less condensation on the inside of the glass.

Explain why.

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(c) Double glazing can be made using two pieces of normal glass with an air gap between them. Better insulating glass (Superglaze or G-type) can be used instead of normal glass. The size of the air gap can also be increased to improve insulation.

A company making double glazing provides some information about their products.

U-values for different types of double glazing

Normal glass Superglaze G-type

6 mm air gap 3.1 2.7 2.6

12 mm air gap 2.8 2.2 2.0

16 mm air gap 2.7 2.0 1.8

For the same size window, under the same temperature conditions, the energy loss halves if the U-value is halved.

Cost of double glazing in £ per m2

Normal glass Superglaze G-type

6 mm air gap 90 110 160

12 mm air gap 100 130 185

16 mm air gap 110 155 210

(i) The data the double glazing company produced is checked and confirmed independently by other scientists.

Suggest why it is important to confirm the data independently.

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(ii) A homeowner is going to replace his old single-glazed windows with new double-glazed windows.

Discuss the cost of fitting double glazing using better insulating glass compared with double glazing using normal glass.

Use the information given in the tables.

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(Total 8 marks)

Q19. The diagram shows the direction of heat transfer through a single-glazed window.

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

Cost to buy and install Estimated yearly savings on energy bills

Estimated lifetime of thedouble-glazed windows

£5280 £160 30 years

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

To gain full marks you must complete a calculation.

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(Total 10 marks)

Q20.The diagram shows how one type of electric storage heater is constructed. The heater has ceramic bricks inside. The electric elements heat the ceramic bricks during the night. Later, during the daytime, the ceramic bricks transfer the stored energy to the room.

(a) (i) Complete the following sentences using words from the box.

conduction convection evaporation

Energy is transferred through the metal casing by .....................................

The warm air rising from the heater transfers energy to the

room by ................................................(2)

(ii) The inside of the metal case is insulated.

Which one of the following gives the reason why?

Tick ( ) one box.

To transfer energy from the ceramic bricks to the room faster

To stop energy from the room transferring into the heater

To keep the ceramic bricks hot for a longer time

(1)

(b) In winter, the electricity supply to a 2.6 kW storage heater is switched on for seven hours each day.

(i) Calculate the energy transferred, in kilowatt-hours, from the electricity supply to the heater in seven hours.

Use the correct equation from the Physics Equations Sheet.


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

(ii) The electricity supply to the heater is always switched on between midnight and 7 am. Between these hours, electricity costs 5 p per kilowatt-hour.

Calculate how much it costs to have the heater switched on between midnight and 7 am.

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

(c) Between 7 am and 8 am, after the electricity supply is switched off, the temperature of the ceramic bricks falls by 25 °C.

Calculate the energy transferred from the ceramic bricks between 7 am and 8 am.

Total mass of ceramic bricks = 120 kg.Specific heat capacity of the ceramic bricks = 750 J/kg °C.



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

(Total 8 marks)

Q21. A student has read that a solar cell with a dirty surface will not work as well as a solar cell

with a clean surface.

To test the effect of a dirty surface on a solar cell, the student set up the following equipment.

The student put the desk lamp a fixed distance from the solar cell. To represent the effect of a dirty surface, the student covered the surface of the solar cell with pieces of tracing paper. Each time the student added a piece of paper, she measured the output voltage of the solar cell.

(a) The results taken by the student have been used to draw the graph below.

(i) One of the results seems to be anomalous.

Draw a ring around the anomalous data point on the graph.(1)

(ii) The larger the number of sheets of tracing paper used, the lower the intensity of the

light reaching the solar cell.

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

a decrease in

A decrease in the intensity of the light reaching the solar cell causes no change to

an increase in

(1)

the output voltage from the solar cell.

(b) People can buy panels of solar cells to generate electricity for their homes.Any surplus electricity can be sold to the electricity supply company.

(i) Give one environmental advantage of generating electricity using solar cells rather than generating electricity in a coal-burning power station.

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(ii) A homeowner pays £7600 to have solar panels fitted on the roof of their house.The homeowner expects to save £950 each year from reduced energy bills and from selling the electricity.

Assuming these figures to be correct, calculate the pay-back time for the solar panels.


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

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

decrease

Allowing the surface of the solar panels to become very dirty will not change

increase

the pay-back time.(1)

(iv) Explain your answer to part (b)(iii).

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(Total 8 marks)

Q22.The diagram shows a car radiator. The radiator is part of the engine cooling system.

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

(a) Why is the radiator painted black?

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

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

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

Explain how.

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

Calculate the energy transferred each second from the coolant.

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


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Energy transferred each second = .............................................................. J

(3)

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

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

Draw a ring around the correct answer.

decreases the

efficiencydoes not change the

efficiencyincreases the

efficiency


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(Total 9 marks)

Q23.Diagram 1 shows the energy transferred per second from a badly insulated house on a cold day in winter.

Diagram 1

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

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

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

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

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

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

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


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

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

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

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

Calculate the cost of heating the house for one day.

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

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

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

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

Time of day

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

Between midnight and 6 am the rate of energy transfer from

decreases.

the house decreases then stays constant.

increases.

Give the reason for your answer.

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

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

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

Diagram 2 Diagram 3

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

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

Explain why.

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

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

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

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

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

What is meant by the term U-value?

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

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

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

U-value of the wall = 0.3

U-value of glass doors = 1.8

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

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

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

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

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

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

(Total 11 marks)

Q24.The diagram shows the design of a solar cooker. The cooker heats water using infrared radiation from the Sun.

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

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

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

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


black silver white


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

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

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

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

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

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

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

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


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

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

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

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

(Total 6 marks)

Q25.An electric immersion heater is used to heat the water in a domestic hot water tank.When the immersion heater is switched on the water at the bottom of the tank gets hot.

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

Explain how.

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

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

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

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

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

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

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

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

(b) Complete the following sentence.

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

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

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

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

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

Time in hours

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

Explain why.

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

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

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

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

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

Calculate the mass of water in the tank.

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

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

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

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

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

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

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

Time in hours

An insulating jacket only costs £12.

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

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

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

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

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

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

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

(Total 13 marks)

Q26.(a) A student used the apparatus drawn below to investigate the heating effect of an electric heater.

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

Graph A shows how the student expected the temperature of the metal block to

change after the heater was switched on.

Describe the pattern shown in Graph A.

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

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

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

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

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

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

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

Suggest one reason why.

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

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

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

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


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

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

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

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

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

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

Metal Specific heat capacity in J/kg°C

Aluminium 900

Iron 450

Lead 130

Which one of the metals will heat up the most?


aluminium iron lead

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

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

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

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

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

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

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

conduction.

Energy is transferred through the water by convection.

evaporation.

conduction.

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

evaporation.

(2)

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

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

Calculate the pay-back time for the insulating jacket.

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

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

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

(Total 11 marks)

Q27.The diagram shows three cups A, B and C.

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

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

condensation conduction convection

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

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

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

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

The results are shown on the graph.

Time in minutes

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

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

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

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

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

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

Using the graph, give a reason for your answer.

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

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

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

The same starting temperature and volume of water were used.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

(4)(Total 16 marks)

M1. (a) (heat) is conducted through the glassthe answers must be within the context of the question

1

(heat) passes through glass and air by radiationboth glass and air required

1

(heat) crosses the air gap by convectionmention of conduction through air is neutral

1

(b) any one from

lightaccept sunlight

gamma rays

X-rays

radioaccept sound or ir or microwaves or electromagnet waves

1

(c) any two from

cuts down convection currentsaccept stops air moving

air pockets trap air (from moving)accept has air pocketsdo not accept stops heat moving or traps heat

foam is a poor conductorair in the foam is a good insulatoraccept air is a good insulator in air pockets for both marks

2

(d) evaporation (of the water)do not accept rain is cold

1

takes energy from the houseaccept takes heat away or higher energy molecules leave first

1[8]

M2. (a) (i) (insulate it) with fibre glass or foamor felt or polystyrene beads orrockwool or (aluminium) foil

an example must be includeddo not credit loft insulation

1

(ii) fill the cavity with fibre glass or foamor mineral wool or polystyrene ornamed liner inside wall or makingwalls thicker

an example must be includeddo not credit cavity wall insulation

1

(iii) double glaze or draw the curtains orblinds or thicker glass or secondaryglazing described

do not credit fit smaller windows1

(iv) put in draught excluder (or described)or strip or description of filling gapsor seal gaps or double glazed doorsor build porch or curtains inside dooror mat under door

do not credit just carpetaccept buy new doorsaccept premise that gap is between frame and wall as well as between frame and door

1

(b) windy or stormy or wet or snow orrain or sleet or hail or fog or mist

do not credit frosty1

[5]

M3. (a) insulationallow example e.g fibreglass

1

double glazingallow curtains

1

draught excluderallow double glazing / close fitting doorallow turning down thermostat once only / turn down the heating

1

(b) transfers more useful energyallow converts more energy into light / less into heat / less energy wasted

1[4]

M4. (a) loft insulation1

energy saved in 10 years £6001

net saving (600 – 110) £4901

OR

hot water jacket1

energy saved in 10 years £1401

This is the highest percentage saving on cost1

(b) transferred to environment / surroundings1

as heat / thermal energy1

[5]

M5. (a) (i) £150gets 2

Else 1000 – (250 + 350 + 100 + 150) or 1000 – 850gets 1

2

(ii) (Named) floor coveringOR Insulation under floor

for 1 mark1

(b) (i) Draught proof doors or fibre glass in loft or in cavityFor draught proofing

gains 1 mark

Very low cost/easy to installRepays for itself quickly/cost recuperated quicklyReasonable energy saving

any 2 for 1 mark each

For loft insulation

Second lowest installation cost/easy to installReasonable large energy savings for this costReasonable payback time

gains 1 mark

For foam filled cavityBiggest energy/cash savingCost effective

any 2 for 1 mark each3

(ii) Double glazinggains 1 mark

Costs mostSaves least energyLeast cost effective

any 2 for 1 mark each3

[9]

M6. (a) (i) hot water rises (not heat)for 1 mark

due to convection currentsor water expands/becomes less dense on heatingor less dense water rises

any for 1 mark2

(ii) inside hotter (than outside)

for 1 mark1

(iii) (heat transfer by) conductionfor 1 mark

1

(iv) surround/cover/insulate tank with poor conductor or named insulatorfor 1 mark each

2

(b) (i) air is an insulator/poor conductorfor 1 mark

1

(ii) convection stopped foam is an insulator/poor conductorfor 1 mark each

2[9]

M7. (a) (i) any one from:

water to the mugwater to the airmug to the airmug to the table

both requireddirection of transfer must be correct

1

(ii) when temperatures are the sameaccept a specific example eg when the temperature of the water and mug are the sameaccept radiant heat transfer will never stop

1

(b) wood1

(c) (i) conductionaccept convection if not given as 3rd answer

1

insulator1

convection1

(ii) any one from:do not accept any rebuilding of house

double glazing

loft insulationaccept roof for loft

1

carpets

(cavity) wall insulationdo not accept closing doors and windows

draft excluders

foil behind radiatorsaccept blocking chimney

paint inside walls white[7]

M8. (a) (i) convection current correctly shownwith arrows extending to aboveinsulation label line

circulation must show water rising in the left half of the tank accept continuous or broken arrows must be at least one arrow up andone arrow downallow 1 mark for correct diagram which does not extend high enough

2

(ii) it expands or it gets less densedo not allow hot water risesdo not accept explanation in terms of molecules expanding orchanging densitydo not accept lighter or heavier

1

more dense water fallsallow cold water falls if qualified with a suitable reason

1

(b) (i) reflects heat back into the room or where it came fromaccept infrared or radiation or energy for heataccept bounce for reflect if in correct context

1

(ii) air is a (good) insulator or poor conductor or air stops conductiondo not accept plastic foam is a good insulator or bad conductor

1

air is trapped1

convection loss reduced or stopped1

(c) two out of the following three:any answer which gains credit must contain a comparison

rate of evaporation decreasesaccept less sweat can evaporate or evaporation is more difficult

less heat energy removed from the body

higher humidity the less water vapour can be absorbed (into the air)accept sweat for water vapourdo not credit description of high humidityaccept a correct answer in terms of dynamic equilibrium

2[10]

M9. (a) (i) 201

(ii) convection1

(iii) fit draughtproof strips1

accept lay carpetaccept fit curtainsaccept close doors / windows / curtainsaccept any reasonable suggestion for reducing a draught‘double glazing’ alone is insufficient

(b) air is (a good) insulator1

or air is a poor conductoraccept air cavity / ‘it’ for air

reducing heat transfer by conductionaccept stops for reducesignore convection

do not accept radiationdo not accept answers in terms of heat being trapped

1

(c) (i) most cost effectiveaccept it is cheaper or lowest costaccept shortest payback timeaccept in terms of reducing heat loss by the largest amountdo not accept it is easierignore most heat is lost through the roof

1

(ii) 41

[7]

M10. (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]

M11. (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]

M12. (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]

M13. (a) 11

(b) 3 and 4or1 and 2

1

(c) U-values for the 20 mm windows are the same or higherthan those for the 16 mm windows

1

therefore the 20 mm windows are no more energy efficientthan 16 mm windows

accept so the 16 mm windows are as energy efficient as 20 mm windows

1

(d) 1 and 2must have both and no other

1

(e) Type B glass transmits less infrared than Type A glassaccept radiation / heat for infraredaccept Type B glass absorbs more infrared than Type A glass

1

and as infrared has a heating effect the conservatory willremain cooler

1[7]

M14. (a) (i) wallsaccept sides (of house)

1

(ii) fit double glazingorclose / fit curtains / fit shutters

accept close windowsaccept keep house at a lower temperatureaccept fit (foam) draft excluders around the windows / in the jamsaccept put plastic (film) across the windowsdo not accept fit thicker glass

1

(b) (i) cavity (wall insulation)accept the middle one

1

(ii) fit hot water jacket and draught-proofingboth required

1

(together) saves most moneyonly scores if first mark scoresaccept saves more than fitting (energy efficient) light bulbsaccept saves £40accept gives the shortest payback timean answer fit energy efficient light bulbs (on its own) gains 1 mark only

1[5]

M15. (a) (i) 2(.0)accept 2000 W or 2000 watt(s)accept answer given in tabledo not accept 2000

1

(ii) 4.5allow 1 mark for correct substitutionie 1.5 × 3allow 1 mark for the answers 1.5 or 6(.0)

2

(iii) 54ortheir (a)(ii) × 12 correctly calculated

allow 1 mark for correct substitutionie 4.5 × 12ortheir (a)(ii) × 12allow 1 mark if correct answer is given in pounds eg £54

2

(b) (i) 6 pm1

temperature starts to rise fasteronly scores if 6 pm given

orgraph (line) is steeper / steepest

it refers to graph gradient or temperatureaccept answers in terms of relative temperature riseeg 5 to 6 pm 2 °C rise, 6 to 7 pm 6 °C riseaccept temperature rises sharply / rapidly / quicklydo not accept temperature starts to rise

1

(ii) middle box ticked1

[8]

M16. (a) 851

(b) (i) thickness (of glass)accept how thick the glass isdo not accept light intensity

1

(ii) transmits less infra redaccept radiation / or heat for infra redaccept transmits less energy (at all wavelengths)accept (glass B) absorbs more infra redaccept infra red is the same as heatignore reference to visible light

1

infra red has a heating effectorinfra red warms the room

ignore references to conservatorykeeping cool

1

(c) Z1

[5]

M17. (a) total saving shown for each methodie:cavity wall £325jacket £163central heating £90

allow 1 mark for one correctly calculated valueorallow 1 mark for showing energy bill savings for each method over 5 yearsie:cavity wall £575jacket £175central heating £400there are no marks for calculation of payback time

2

(b) energy cannot be destroyedaccept energy is conservedignore reference to created

1

(c) 4 (hours)allow 1 mark for obtaining number of kWh = 10or energy transferred = 10

2[5]

M18. (a) (kinetic) energy (of the particles) is reducedaccept slow downaccept transfer energy to (cold) glass / surfaceaccept energy is lostdo not accept vibrate less

1

move closer together1

(b) double glazing provides (better) insulationaccept double glazing has a lower U-valueaccept less energy / heat transfer through double glazing

1

(inside of) glass is not as coldaccept window stays warm(er)

1

(c) (i) any one from:

• to avoid bias

• to make sure results are reproducibleaccept repeatable / reliable for reproducible

1

(ii) any three from:accept Superglaze or G-type for ‘better insulating glass’ throughout

• the lower the U-value, the better the insulator‘better insulating glass’ has a lower U-value is insufficient

• better insulating glass costs more money

• increasing the (width of) air gap increases cost

• additional cost of better insulating glass offset by energy savings3

[8]

M19. (a) (i) conduction1

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

oratoms vibrate with a bigger amplitude

accept vibrate faster / moredo not accept start to vibrate

oratoms collide with neighbouring atoms

1

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

ormaking these other atoms vibrate with a bigger amplitude

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

1

(b) (i) 5 (°C) to 25 (°C)either order

1

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

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

2

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

2

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

1

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

this is less than cost of windows (1)or

= 176 (1)

this is more than the yearly savings (1)1

[10]

M20. (a) (i) conduction1

convection1

correct order only

(ii) to keep the ceramic bricks hot for a longer time1

(b) (i) E = P × t

18.2

allow 1 mark for correct substitution ie 2.6 × 7 provided that no subsequent step is shown

2

(ii) 91 (p)or their (b)(i) × 5 correctly calculated

accept £0.91do not accept 0.91 without £ sign

1

(c) E = m × c × θ

2 250 000allow 1 mark for correct substitution ie 120 × 750 × 25 provided that no subsequent step is shownanswers 2250 kJ or 2.25 MJ gain both marks

2[8]

M21. (a) (i) correct data point identified (4, 0.96)1

(ii) a decrease in1

(b) (i) no / less atmospheric pollutionaccept specific examples eg no CO2 / greenhouse gases producedaccept no harmful gases / fumesaccept reduced pollution from transportation (of coal)accept does not contribute to global warmingit / they refers to solar cellsdo not accept no / less pollutiondoes not harm the environment is insufficientit is a renewable energy source is insufficient

1

(ii) 8

allow 1 mark for showing correct method ie provided that no subsequent step is shown

2

(iii) increase1

(iv) these marks can score even if (b)(iii) is wrong

less / no electricity generated

accept energy for electricityaccept reduced power / voltage output

1

(because) lower light intensity (hitting solar panel / cell)orso decreases money paid / gained (from selling electricity)

allow less light / sun (hitting solar panel / cell)1

[8]

M22.(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]

M23.(a) (i) 5(.0)1

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

2

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

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

1

(iv) decreases1

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

1

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

1

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

1

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

1

(c) it will increaseroom will be cooler is insufficient

1

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

1[11]

M24.(a) to reflect (the infrared)accept (shiny surfaces) are good reflectorsignore reference to incorrect type of wave

1

(b) black1

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

1

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

orso temperature of water increases faster

accept to heat water faster accept cooks food faster

orreduces loss of water (by evaporation)

1

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

2[6]

M25.(a) (water) particles / molecules gain energy / move fasteraccept atoms for moleculesignore move more do not accept move with a bigger amplitude / vibrate more

1

and (the particles / molecules) move apart1

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

1

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

1

(b) conduction1

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

accept the water is hottest / hotter1

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

1

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

or

correctly calculating temperature fall as 8°C

or

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

answers of 0.12, 19.2 or 16.6 gain 2 marks

answers of 0.019 or 0.017 gain 1 mark3

(iii) water stays hot for longer1

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

1

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

1[13]

M26.(a) (i) temperature (increase) and time switched on are directly proportionalaccept the idea of equal increases in time giving equal increases in temperatureanswers such as:• as time increases, temperature increases• positive correlation• linear relationship• temperature and time are proportionalscore 1 mark

2

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

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

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

• (metal) block is not insulated1

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

2

(b) leadreason only scores if lead is chosen

1

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

1

(c) (i) convectioncorrect order only

1

conduction1

(ii) 3 / 4 (year)

or

allow 1 mark for correct method, ie shown

0.75

or

9 months

or

274 days2

[11]

M27.(a) conductionmust be in correct order

1

convection1

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

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

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(iii) C1

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

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

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

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

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

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to escape from the surface of the water1

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

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

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E1. Foundation Tier

Again this was a poorly answered question. In part (a), even those candidates who understood the mechanisms of conduction, convection and radiation failed to apply their knowledge to the situation described in the question.

Most candidates were able to pick up a mark in part (b) for mentioning light or sound. In part (c) very few mentioned trapped air in the cavity wall insulation.

The cooling effect of evaporation in part (d) appears to be little known. Again, those candidates who mentioned evaporation often failed to relate this knowledge to the particular context of the question.

Higher Tier

Although candidates showed good knowledge of the mechanisms of the three transfer processes in part (a), it was poorly answered in the context of the question. Candidates had considerable trouble expressing themselves coherently. Few attained the radiation mark. There may have been some confusion, since pupils are taught that double glazing reduces heat loss but science must be capable of being applied as well as regurgitated. Some candidates thought the diagram showed a window with an air gap open at the top. Many candidates described convection within the room or radiation from a radiator or from the Sun. Some had warm air ‘going’ through the glass.

A pleasing number of candidates answered part (d) well, though many failed to link energy ‘needed’ with evaporation.

E2. The answers to part (a) of this question tended to be very brief, with the single word insulation being a common response. Candidates often failed to note that the rubric asked them to describe what could be done, rather than simply to state. Strangely, in part (b), many candidates suggested that hot weather would make it difficult to keep a house warm.

E3. (a) This part was generally well done but weaker candidates gave ‘insulation’ or ‘double glazing’ indiscriminately.

(b) This was less well answered, with most being in terms of ‘using less energy’ or ‘lasting longer’.

E4. (a) This part was well answered. Most candidates were able to identify loft insulation as the most effective method and provided calculations supporting this conclusion.

(b) A surprising number made no reference to heat/thermal energy in their responses.

E5. This Question was well answered by the vast majority of candidates.

(a) A very small minority were unable to calculate the floor heat loss as £150. A few did not gain a mark for answers of 150. In part (ii)a small minority of candidates failed to appreciate that “this loss” referred to the heat loss through the floor rather than general heat loss from a house. Answers based on heat loss from other areas of the house were not credited.

(b) The vast majority of candidates gained all six marks and only a very small minority failed to gain any marks. Although not needed, a good number of candidates introduced the idea of “pay back time” in their answers.

E6. In part (a)(i) very many candidates referred to heat rising and failed to score the marks, a few referred to steam rising and fewer again actually made the scoring point that hot water rises. Very few candidates went on to score the additional mark by enhancing their explanation with further relevant detail such as “due to convection” or “to be replaced by cooler water falling” or any attempted explanation by way of reference to change of density. In part (ii) very few candidates scored the mark by making reference to the fact that the tank and hot water were at a higher temperature than the surroundings. Part (iii) produced more correct answers, although “conduction” was not offered as the answer by most candidates. The distraction here, whatever it was was not convection or radiation for a significant number of candidates. The candidates found more success in part (iv) with most gaining at least one mark and many both marks.

In part (b)(i) the reason why a cavity wall reduces heat loss, mainly because it contains air which is a bad conductor, was beyond most candidates. In part (ii) a mark was frequently obtained for foam being an insulator, but appreciation that filling the cavity with foam would reduce convection losses was rare.

E7. In part (a), the majority of candidates were able to identify from the word box the suitable sources and destinations for the heat energy but only a minority appreciated that heat transfer continues until temperatures become equal. In part (b) wood was generally correctly identified as the renewable type of fuel. The theory and practice of reducing heat energy loss from a house was widely understood. However a significant number of candidates apparently thought that electric currents pull cold air into a room.

E8. Foundation Tier

This question was poorly answered, with few candidates showing any more than a minimal knowledge of heat transfer. In part (a)(i) few candidates were able to draw a correct convection current. Most candidates simply drew a line joining the cold water inlet to the hot water outlet. Many of the explanations given in part (a)(ii) were in terms of the particles or molecules expanding. In part (b)(i) many candidates were insufficiently concise to gain the mark, making only general comments about reflection. Some referred, erroneously, to the conduction properties of aluminium and also to it being a poor emitter. In part (b)(ii) too many candidates referred to the plastic foam as a good insulator. Few recognised the reduction in conduction and convection due to the air being unable to move. Part (c) was poorly answered. A popular error was to suggest that high humidity caused a person to sweat even more so that the person felt even more uncomfortable. Only the better candidates were able to relate a reduced rate of evaporation to reduced heat loss.

Higher Tier

This question was poorly answered with few candidates showing any more than a minimal knowledge of heat transfer. In part (a)(i) few candidates were able to draw a correct convection current, common errors occurred where the specific position of the heat source had been ignored. Part (a)(ii) was answered well by the more able candidates, however, the weaker candidates often gave explanations in terms of ‘molecules expanding’ or ‘heat rising’. In part (b)(i) many candidates were insufficiently concise to gain the mark, making only general comments about reflection. Some referred, erroneously, to the conducting properties of aluminium and also to it being a poor emitter. In part (b)(ii) too many candidates referred to the plastic foam as a good insulator while few recognised the reduction in conduction and convection due to the air being unable to move. Part (c) was poorly answered. Only the better candidates were able to relate a reduced rate of evaporation to reduced heat loss.

E9. In part (a) the calculation of the energy lost through lack of draught proofing was generally successful and many candidates were able to submit appropriate ideas and techniques to limit heat transfer by draughts. Answers to part (b) were poor with few candidates being able to give an explanation in terms of air being able to reduce heat loss by conduction. Many answers referred to radiation. In part (c) many candidates were able to use the information to give an answer in terms of cost efficiency. However a significant number of candidates simply answered in terms of hot air / heat rising.

E10. 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.

E11. 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”.

E12. (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.

E14. (a) (i) Most candidates identified the walls as being the part through which most heat is lost.

(ii) Most candidates opted for double glazing as a method for reducing heat loss through the windows.

(b) (i) Most candidates correctly selected cavity wall insulation as the method that would reduce the yearly energy bill the most.

(ii) Only the better candidates realised that by buying a hot water tank jacket and fitting draught-proofing, the householder would save the most money each year. Some candidates, perhaps believing that the householder could only buy one item, opted for the energy-saving light bulbs: this option however would not save as much money. A few candidates decided to buy 4 hot water tank jackets with the £60.

E15. (a) (i) Surprisingly, only just over half of the candidates realised that the high setting would be obtained by adding together the low setting and the medium setting. Some candidates were looking for a pattern and, thinking that each power increased by 1.0, arrived at the answer 2.5.

(ii) Pleasingly nearly three quarters of candidates were able to complete this calculation correctly.

(iii) Only the better candidates could arrive at the correct answer to this calculation. Many candidates simply multiplied the cost per kilowatt-hour by the number of hours instead of by the number of kilowatt-hours, thus arriving at an answer of 36.

(b) (i) Generally most candidates opted for the correct answer of 6.00 pm, although the reason given was often too vague to deserve a mark. Candidates often stated that .that was when the temperature went up., in spite of the fact that the temperature had been increasing throughout the previous hour. A common mistake was to say that the heater was switched on at 7.00 pm because ‘that was when the temperature was the hottest’.

(ii) Just over two thirds of candidates realised that if the temperature of the room was

not changing then the room is losing energy as fast as the heater supplies energy.

E16. (a) Many candidates gave a correct answer to this question. However, a significant number of candidates supplied an answer that was in excess of 100 %.

(b) (i) The better candidates were able to identify the thickness of the glass as being the variable that had been controlled, but many other candidates thought that it was the light intensity that had been controlled.

(ii) Many candidates scored 1 mark on this question, but very few candidates made the connection between infrared radiation and the heating effect sufficiently clear. There was also confusion between transmission, absorption and reflection.

(c) Only just over half of the candidates scored this mark, Y was a popular incorrect choice.

E17. (a) Many candidates answered this well. A common error was failing to realise that the question had referred to a period of 5 years; also, simple arithmetical mistakes were not uncommon, particularly when subtracting the installation cost from the energy saving. A significant number of candidates made up their own question and worked out payback times.

(b) Just under half of the candidates were able to state that energy cannot be destroyed or that energy is conserved.

(c) Candidates generally found this calculation difficult, as they had to work back from the cost. Very few seemed to be able to do this in a logical way. A common incorrect response was 10 hours, indicating that perhaps candidates realised they could get 10 kWh for their £2; however, calculations were often just a jumble of numbers, so it was difficult to credit any steps in the working.

E18. (a) Many students were able to identify that the particles would lose energy. Whilst the idea of the particles moving closer together appeared to be understood, answers referring to the particles 'becoming denser' were quite common.

(b) A significant number of students appear to have misconceptions about double glazing,

often relating to it 'not letting the water vapour through'. Just over a tenth of students were given full marks.

(c) (i) The idea of avoiding bias was correctly identified by many students, although some have a dim view of double glazing companies who will ‘lie about their results’.

(ii) Many students found it difficult to analyse the given data. A large number of responses merely quoted the data rather than summarising it, although quite a few managed to state somewhere that the better insulating glass was more expensive. Few responses summarising the effect of the air gap width were seen. A number of students recognised that better insulating glass would lead to a reduction in energy bills, but were not always able to express this idea clearly.

E19. (a) (i) Only a small minority of students (24%) were able to identify ‘conduction’ as the method of heat transfer.

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

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

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

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

(c) This question was reasonably well done and students seemed to have a good knowledge of pay-back time and the economics of fitting double glazing. Many students managed a correct calculation and then went on to give an acceptable reason why this particular situation was not cost-effective. The most common method was to calculate the savings over 30 years (£4 800) and to conclude that this was less than the cost of installation (£5 280), giving a ‘loss’ of £480. There were however, students who did not address the question but simply described how double glazing works and others who had perhaps performed a calculation but given no evidence on their scripts. The latter group should be

made aware that for full credit a complete answer is required.

E20. (a) (i) This was generally well-answered, although the most common mistake was to have conduction and convection the wrong way round.

(ii) Most students chose the correct answer.

(b) (i) Students coped well with this calculation, the majority obtaining the correct answer of 18.2 kWh.

(ii) This calculation however was very poorly answered. A very common answer was to write 7 x 5 = 35.

(c) The majority of Students obtained the correct answer to this calculation, although some students were unable to show the correct number of zeroes.

E21. (a) (i) The vast majority of students were able to correctly identify the anomalous point, although a significant number made no attempt at this question.

(ii) Most students realised that a decrease in light intensity would lead to a decrease in output voltage.

(b) (i) Most students correctly identified the fact that there would be less atmospheric pollution, or less carbon dioxide being emitted. Those who failed to score the mark were either giving very vague general answers such as ‘it is environmentally friendly’ or ‘doesn’t cause pollution’ or were simply stating that it is a renewable resource.

(ii) The great majority of students obtained the correct answer to this calculation. The most frequent mistake was to deduct 950 from 7600, thereby arriving at an answer of 6650 years for the pay-back time.

(iii) Over half of the students thought that allowing the surface of the solar cells to become dirty would decrease the pay-back time. It would appear that there is a common misunderstanding about what is meant by pay-back time.

(iv) Most students were able to score one mark for this question, but only the better students scored both marks. This applied even to those students who thought that the pay-back time would be decreased.

E22.(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.

E23.(a) (i) Many students left this part blank. Around half of the students obtained the correct answer of 5 (kW) and they were often able to go on and obtain both marks in part (ii).

(ii) Many students left this part blank.

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

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

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

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

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

E24.(a) Most students realised that a shiny surface would be a good reflector, but many used the word “bounce” instead of “reflect”. The most common wrong response was to say that metals are good conductors.

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

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

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

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

E25.(a) Less than half of the students scored at least two marks, usually for referring to the hot water becoming less dense and therefore rising. Students who referred to water particles often mistakenly referred to them ‘vibrating more’ as a result of the energy given, or to the particles themselves becoming less dense.

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

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

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

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

E26.(a) (i) Although most students could describe the pattern as being linear, very few referred to the fact that the graph showed direct proportionality.

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

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

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

an adequate reason.

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

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

E27.(a) Nearly all students recognised two situations that represented conduction and convection.

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

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

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

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

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

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

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

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