St Thomas More Catholic School

Q1.The image below shows a student before and after a bungee jump.

The bungee cord has an unstretched length of 20 m.

(a)     For safety reasons, it is important that the bungee cord used is appropriate for the student’s weight.

Give two reasons why.

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

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

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(2)

(b)     The student jumps off the bridge.

Complete the sentences to describe the energy transfers. Use answers from the box.

 

 

elastic potential      gravitational potential      kinetic      sound      thermal

Before the student jumps from the bridge he has a store of

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

When he is falling, the student's store of .......................................... energy increases.

When the bungee cord is stretched, the cord stores energy as

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

M1.(a)     any two from:

•        bungee rope may snap

•        rope may extend too much

•        student may land in the river

2

(b)     gravitational potential

correct order only

1

kinetic

1

elastic potential

1

Q2.Iceland is a country that generates most of its electricity using geothermal power stations and hydroelectric power stations.

(a)     (i)      Complete the following sentences to describe how some geothermal power stations work.

In regions where volcanoes are active, the ground is hot.

Cold ............................................. is pumped down into the ground

and is ............................................. by hot rocks.

It returns to the surface as steam. The steam is used to turn a turbine.

The turbine drives a ............................................. to produce electricity.

(3)

(ii)     Which one of the following statements about geothermal power stations is true?

Tick () one box.

 

Geothermal power stations use fossil fuels.

 

Geothermal power stations produce carbon dioxide.

 

Geothermal power stations provide a reliable source of electricity.

(1)

(b)     What is needed for a hydroelectric power station to be able to generate electricity?

Tick () one box.

 

Falling water

 

A long coastline

 

Lots of sunny days

(1)

(Total 5 marks)

M2.(a)     (i)      water

1

heated

accept boiled or turned to steam

do not accept evaporated

1

generator

1

(ii)     geothermal power stations provide a reliable source of electricity

1

(b)     falling water

1

Q3.The image shows a man using a leaf blower to move some leaves.

The leaf blower is powered by an electric motor connected to a battery.

(a)     Energy transfers take place when the leaf blower is being used.

Use the correct answer from the box to complete each sentence.

 

 

chemical

electrical

kinetic

nuclear

sound

The battery stores ......................................... energy which is transferred into electrical energy.

The electric motor transfers electrical energy usefully into ......................................... energy.

The motor wastes energy as ......................................... energy and as energy that heats the surroundings.

(3)

(b)     The total power input to the leaf blower is 750 W.The useful power output of the leaf blower is 360 W.

Calculate the efficiency of the leaf blower.

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Efficiency = ..................................

(2)

(Total 5 marks)

M3.(a)      chemical

correct order only

1

kinetic

1

sound

1

(b)     48% or 0.48

an answer of 0.48 with a unit gains 1 markan answer of 0.48% gains 1 markan answer of 48 with or without a unit gains 1 mark

2

[5]

Q4.A heater uses energy from a laptop computer to keep a drink hot.

The image shows a metal mug on the heater.

(a)     The laptop computer is operating on battery power.

How would connecting the heater affect the amount of time the laptop computer would operate for, before needing to be recharged?

Tick (✔) one box.

 

 

 

Tick (✔)

 

it would decrease the time

 

 

it would not affect the time

 

 

it would increase the time

 

(1)

(b)     The power output from the heater is 12 W.

Calculate the energy transferred to the metal mug in 60 seconds.

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    Energy = ................ joules

(2)

(c)     The table lists changes that may affect the energy transfer per second from the heater to the liquid.

Tick (✔) one box to show the effect of each change.

 

 

Change

Energy transfer per second to the liquid

 

increases

decreases

does not change

 

use a mug with a smaller base

 

 

 

 

use a lower power heater

 

 

 

 

use a plastic mug instead of a metal mug

 

 

 

(3)

M4.(a)     it would decrease the time

1

(b)     720 (J)

allow 1 mark for correct substitution ie 12 × 60 provided no subsequent step

2

(c)     decreases

1

decreases

1

decreases

1

more than one tick in any row negates the mark

[6]

Q5.A student investigated how much energy from the Sun was incident on the Earth’s surface at her location.

She put an insulated pan of water in direct sunlight and measured the time it took for the temperature of the water to increase by 0.6 °C.

The apparatus she used is shown in the figure below.

 

(a)     Choose the most appropriate resolution for the thermometer used by the student.

 

 

Tick one box.

 

 

0.1 °C

 

 

0.5 °C

 

 

1.0 °C

 

(1)

(b)     The energy transferred to the water was 1050 J.

The time taken for the water temperature to increase by 0.6 °C was 5 minutes.

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

Write down the equation which links energy transferred, power and time.

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

(1)

(c)     Calculate the mean power supplied by the Sun to the water in the pan.

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                  Average power = ............................................. W

(2)

M5.(a)     0.1 (°C)

1

(b)     power = energy transferred / time

allow P = E / t

1

allow E = P × t

(c)     1050 / 300

1

3.5 (W)

1

accept 3.5 (W) with no working shown for 2 marks

Q6.(a)     In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.

A householder wants to reduce her energy bills. She collected information about a number of ways of reducing energy used. The information is shown in the table.

 

 

Ways of reducingenergy used

Cost to buy andinstall in £

Money savedper year in £

 

Install anenergy-efficient boiler

  2 000

320

 

Insulate the loft

     400

200

 

Install double-glazedwindows

12 000

120

 

Install cavity wallinsulation

     415

 145

Use the information in the table to compare the different ways of reducing the energy used. Your answer should include some calculations.

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(6)

M6.(a)     Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also apply a ‘best-fit’ approach to the marking.

0 marksNo relevant information

Level 1 (1-2 marks)There is a relevant statement about an energy saving method

Level 2 (3-4 marks)There is at least one clear comparison of energy saving methods and their cost effectiveness with an appropriate calculation

Level 3 (5-6 marks)There is a comparison of energy saving methods and their cost effectiveness with appropriate calculations. Comparison to include further detail.

examples of physics points made in the response

examples of relevant statements

•        energy efficient boiler saves the most (energy / money) per year

•        loft insulation costs the least to install

•        double-glazing costs the most to install

examples of statements that include cost effectiveness

•        loft insulation is the most cost effective in the long term

•        double-glazing is the least cost effective

•        loft insulation has the shortest payback time

•        double-glazing has the longest payback time

•        payback time calculated for any method

payback times:

energy efficient boiler: 6.25 years

loft insulation: 2 years

double glazing: 100 years

cavity wall insulation: 2.86 years

examples of further detail

•        for cost effectiveness install in the following order: loft, cavity wall, boiler, double-glazing

•        for reducing energy use install in the following order: boiler, loft, cavity wall, double glazing

•        don’t install double-glazing for insulation purposes

•        double-glazing won’t pay for itself in your lifetime

•        justified choice of best / worst method

6

Q7.(a)     In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.

The diagram shows the structure of a vacuum flask.

 

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

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

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(6)

M7.(a)     0 marksNo relevant content.

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

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

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

Examples of the points made in response

accept throughout: heat for energy loss for transfer

plastic cap:

•         plastic is a poor conductor

accept insulator for poor conductor

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

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

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

glass container:

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

•         glass reduces / stops energy transfer by conduction

vacuum:

•         both conduction and convection require a medium / particles

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

•         vacuum stops energy transfer by conduction / convection

silvered surfaces:

•         silvered surfaces reflect infrared radiation

accept heat for infrared

•         silvered surfaces are poor emitters of infrared radiation

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

•         silvered surfaces reduce / stop energy transfer by radiation

6

Q8.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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(2)

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

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

 

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

Explain how.

(2)

M8.(a)     (matt) black is a good emitter of infrared / radiation

accept 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 mark

black emits most radiation / black is the best emitter of radiation for 2 marks

1

(b)     the fins increase the surface area

accept heat for energy

1

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

1

(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 efficiency

does not change the efficiency

increases the efficiency

Give a reason for your answer.

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(2)

(Total 9 marks)

(c)     114 000

allow 1 mark for correct temperature change, ie 15 (°C)

or

allow 2 marks for correct substitution, ie 2 × 3 800 × 15

answers of 851 200 or 737 200 gain 2 marks

or

substitution 2 × 3800 × 112 or 2 × 3800 × 97 gains 1 mark

an answer of 114 kJ gains 3 marks

3

(d)      increases the efficiency

1

less (input) energy is wasted

accept some of the energy that would have been wasted is (usefully) used

or

more (input) energy is usefully used

accept heat for energy

1

[9]

Q9.          (a)     The diagram shows two switches on a room heater. The heater has three power settings. The power produced by two of the settings is given in the table.

 

Setting

Power in watts

Low

700

Medium

1400

High

 

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

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

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

                        Power = ......................................................... kilowatts

(1)

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

Calculate the energy transferred from the mains to the heater in 1½ hours.

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

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                         Energy transferred = ....................................................

(3)

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

What is meant by a device being very efficient?

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

(1)

M9.         (a)      (i)     2.1

correct answer only

1

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

allow 1 mark for correct substitution

ie 2.1 × 1.5

or

their (a)(i) × 1.5

2

kilowatt-hour

accept kWh

or

a substitution 2100 × 5400 scores 1 mark

2100 × 5400 incorrectly calculated with answer in joules scores 2 marks

an answer of 11 340 000 scores 2 marks

an answer of 11 340 000 J scores 3 marks

1

(iii)    most (input) energy is usefully transformed

accept does not waste a lot of energy

accept most of the output / energy is useful

do not accept it does not waste energy

1

 

Q10.A student finds some information about energy-saving light bulbs.

(a)     A 30W light bulb uses 600J of electrical energy in a certain period of time. In that time, it produces 450 J of light energy. The rest of the energy is wasted.

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

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

Wasted energy = ................................. J

(1)

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

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(1)

(iii)    Calculate the efficiency of this light bulb.

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

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

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Time = ......................... s

(2)

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

The table shows some of this information.

 

 

 

Power in watts

Lifetime in hours

Cost of bulb in £

 

Filament bulb

60

  1250

  2.00

 

LED bulb

12

50 000

16.00

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

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(1)

M10.(a)     (i)      150

1

(ii)     transferred to the surroundings by heating

reference to sound negates mark

1

(iii)    0.75

450 / 600 gains 1 mark

accept 75% for 2 marks

maximum of 1 mark awarded if a unit is given

2

(iv)    20 (s)

correct answer with or without working gains 2 marks

correct substitution of 600 / 30 gains 1 mark

2

(b)     (i)      to avoid bias

1

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

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

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

Use the information given in the table.

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(2)

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

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(1)

(Total 10 marks)

(ii)     use less power and last longer

1

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

or

filament costs (5 times) more in energy consumption

1

(iii)    any one from:

•        availability of bulbs

•        colour output

•        temperature of bulb surface

1

[10]

Q11.A small community of people live in an area in the mountains.

The houses are not connected to the National Grid.

The people plan to buy an electricity generating system that uses either the wind or the flowing water in a nearby river.

Figure 1 shows where these people live.

Figure 1

 

© Brian Lawrence/Getty Images

(a)     It would not be economical to connect the houses to the National Grid.

Give one reason why.

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

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(1)

(b)     Information about the two electricity generation systems is given in Figure 2.

Figure 2

 

 

The wind turbine costs £50 000 to buy and install.

The hydroelectric generator costs £20 000 to buy and install.

The average power output from the wind turbine is 10 kW.

The hydroelectric generator will produce a constant power output of 8 kW.

Compare the advantages and disadvantages of the two methods of generating electricity.

Use your knowledge of energy sources as well as information from Figure 2.

(6)

M11.(a)     any one from:

•     high cost of installing overhead power lines or underground cables or pylons

•     high cost as (very) long cables needed

•     amount of electricity required is too low

allow not enough (surplus) electricity would be generated

1

(b)    

Level 3 (5 – 6 marks):

clear comparison of advantages and disadvantages of each method

Level 2 (3 – 4 marks):

at least one advantage and one disadvantage is stated for one method and a different advantage or disadvantage is stated for the other method

Level 1 (1 – 2 marks):

at least one advantage or one disadvantage of either method

examples of physics points made in the response

Advantages of both methods:

•     both renewable sources of energy

•     both have no fuel (cost)

•     both have very small (allow 'no') running costs

•     no carbon dioxide produced

accept carbon neutral

accept no greenhouse gases

accept doesn't contribute to global warming

Advantages of wind:

•     higher average power output

produces more energy is insufficient

Advantages of hydroelectric:

•     constant / reliable power (output)

•     lower (installation) cost

Disadvantages of wind:

•     higher (installation) cost

•     variable / unreliable power output

•     (may) kill birds / bats

Disadvantages of hydroelectric:

•     lower power output

•     (may) kill fish or (may) damage habitats

•     more difficult to set up (within river)

Disadvantages of both methods:

•     (may be) noisy

•     visual pollution

ignore payback time unless no other relevant points made

ignore time to build for both

6

Q12.The image shows a solar thermal power station.

© Kim Steele/Photodisc/Thinkstock

Energy from the Sun is directed at the solar receiver by many mirrors.

(a)     (i)      Suggest one reason why a solar thermal power station is built in a hot desert.

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(1)

(ii)     Complete the following sentence to describe how the mirrors direct energy from the Sun towards the solar receiver.

Energy from the Sun is ................................................... by the mirrors

towards the solar receiver.

(1)

(iii)    Heated water is used to generate electricity in the solar thermal power station.Choose the correct answer from the box to complete each sentence.

 

 

boiler

motor

transformer

turbine

At the solar receiver, water is heated in a ........................................

which turns the water into steam. The steam turns a

....................................which is connected to a water into steam. The

steam turns a .................................... which is connected to a generator.

The generator produces electricity. A ........................................ is used

to change the voltage for transmission along power lines.

(3)

M12.(a)     (i)      high levels of infrared radiation (from the Sun)

allow lots of (solar) energy (available)

do not accept ‘heat’ for infrared

‘it is hot’ is insufficient ‘lots of sunlight’ is insufficient

1

(ii)     reflected

1

(iii)    boiler

correct order only

1

turbine

1

transformer

1

(b)     A solar storage power station is a new type of solar power station.It is able to store energy from the Sun to generate electricity at night.

The solar storage power station can supply a town with a maximum electrical power of 140 000 kW for 15 hours.

Calculate the maximum energy, in kWh, stored by the solar storage power station.

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Energy = ............................................................ kWh

(2)

(c)     A different method of generating electricity uses wind turbines.A student researching a wind farm wrote the following.

 

 

Top Hill Wind Farm has 25 wind turbines.Last week, one of the wind turbines generatedelectricity for only 42 hours out of a possible 168 hours.My conclusion is that all wind turbines operate for only25% of the time.

(i)      Give two reasons why the student is not correct in reaching his conclusion.

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

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

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(2)

(ii)     Give one reason why wind turbines do not generate electricity all the time.

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(1)

(iii)    Give one advantage of using wind turbines to generate electricity compared with using fossil fuel power stations.

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(1)

(Total 11 marks)

M12

(b)     2 100 000 (kWh)

allow 1 mark for correct substitution i.e. 140 000 × 15 provided no subsequent step

2

(c)     (i)      only 1 wind turbine was considered

accept only one location is considered

1

or

other wind turbines may have generated more electricity

accept insufficient sample size

only 1 week’s weather was reported on

or

wind speed varies from one week to another

‘wind speed varies’ is insufficient

1

(ii)     any one from:

•        wind speed is too high / low

allow no windallow too windy

•        wind is unreliable.

allow wind is variable

1

(iii)    any one from:

•        wind is a renewable energy source

•        do not use fuel

•        energy source is free

•        do not release carbon dioxide

•        do not release greenhouse gases

•        do not release sulfur dioxide

•        do not cause acid rain

•        do not cause climate change

•        do not cause global warming

•        do not cause global dimming.

answer must be an advantage of wind, converse answers in terms of fossil fuels are insufficient

accept do not release pollutant gases

‘no pollution’ is insufficient

1

[11]

Q13.          Antarctica is a huge land mass surrounding the Earth’s south pole. It is covered in a very thick layer of ice and is the only remaining large area of the Earth’s surface that has not been affected very much by humans.

There are, however, teams of scientists from various countries studying Antarctica. These scientists need electricity for lighting, for their computers and other scientific instruments and to communicate, via satellite, with the rest of the world. The temperature in Antarctica is always sub-zero, so the scientists need some way of keeping their buildings warm. They also need fuel to be able to get around on their snowmobiles.

Scientists cannot avoid affecting the environment. However, they want to affect it as little as possible.

Atmospheric pollution produced in one country eventually affects the whole of the Earth’s atmosphere. The hole that appears each year in the ozone layer above Antarctica, for example, is mainly caused by pollutants such as CFCs from countries in the northern half of the Earth.

M13.          ideas that

•        direct solar radiation will provide enough energy to heat the (specially designed) buildings during the period Oct-Mar / summer

•        solar cells will produce plenty of electricity in Oct-Mar / summer (when wind generators produce little)

•        a couple of wind generators will produce all electricity needed (for all but heating) Apr-Oct / winter

•        number required makes wind generators unsuitable for heating / buildings

•        no solar energy in June and July / little in winter

•        solar / wind have little effect on environment

•        or  cause no air pollution

•        solar and wind complement each other

•        or  together provide energy all year

•        fuel / gas / diesel can provide energy all the time / at any time

•        fuel / gas / diesel needed for transport

•        fuel / gas / diesel needed for heating in winter

•        diesel has to be imported

•        diesel likely to freeze

•        gas wouldn’t have to be imported

•        drilling for gas difficult / harms environment

•        but atmospheric pollution a global rather than local matter so any produced in Antarctic doesn’t matter much

          (deduct 1 mark (to minm. zero) for incorrect claims about destroying ozone layer)

•        gas produces less carbon dioxide (for the same energy released) than diesel*

•        gas produces less sulphur dioxide (for the same energy released than diesel*

          (* these ideas met by candidates in Q.16 so must be allowed, though not required)

any ten for 1 mark each

[10]

Discuss the advantages and disadvantages of using the following energy sources to meet the scientists’ needs:

•        solar energy

•        energy from the wind

•        natural gas (present in large quantities deep down in the Antarctic land mass)

•        diesel oil (which would have to be imported)

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(Total 10 marks)

 

M13.          ideas that

•        direct solar radiation will provide enough energy to heat the (specially designed) buildings during the period Oct-Mar / summer

•        solar cells will produce plenty of electricity in Oct-Mar / summer (when wind generators produce little)

•        a couple of wind generators will produce all electricity needed (for all but heating) Apr-Oct / winter

•        number required makes wind generators unsuitable for heating / buildings

•        no solar energy in June and July / little in winter

•        solar / wind have little effect on environment

•        or  cause no air pollution

•        solar and wind complement each other

•        or  together provide energy all year

•        fuel / gas / diesel can provide energy all the time / at any time

•        fuel / gas / diesel needed for transport

•        fuel / gas / diesel needed for heating in winter

•        diesel has to be imported

•        diesel likely to freeze

•        gas wouldn’t have to be imported

•        drilling for gas difficult / harms environment

•        but atmospheric pollution a global rather than local matter so any produced in Antarctic doesn’t matter much

          (deduct 1 mark (to minm. zero) for incorrect claims about destroying ozone layer)

•        gas produces less carbon dioxide (for the same energy released) than diesel*

•        gas produces less sulphur dioxide (for the same energy released than diesel*

          (* these ideas met by candidates in Q.16 so must be allowed, though not required)

any ten for 1 mark each

[10]

Q14.          The map below shows the position of two towns, A and B, on the banks of a large river estuary.

A is an important fishing and ferry port.

The wind usually blows from the west. The major roads and railways are shown.

A power station is to be built in area X to generate electricity for the region.

The choice is between a nuclear power station and a coal fired power station.

(a)     State the advantages and disadvantages of the two methods of generating electrical energy.

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(6)

M14.          (a)     must give one advantage and one disadvantage of each to get 4 marksand 2 further scoring pointsAdvantages and disadvantages relevant to:(1) health risk(5) cost(6) environmental factors(7) transport/ storagee.g. common coal / nuclear – high cost of building both

          anti-nuclear examplesnuclear fuel transported on roads/rail in regionpossible effects on public health in surrounding areahigh cost of de-commissioninglong life very active waste materials producedhow waste materials stored safely for a long time

          anti-coal examplesunsightlypollutionsupplies of fuel limitedacid rainnon-renewable

          pro-nuclear examplesfuel cheapno foreseeable fuel shortage

          pro-coal examplessafereliablelarge coal reservesdisposal of solid waste is easier

to max 6

6

Q15.         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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(3)

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

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(2)

(Total 5 marks)

M15.          (a)     loft insulation

1

          energy saved in 10 years £600

1

          net saving (600 – 110) £490

1

OR

          hot water jacket

1

          energy saved in 10 years £140

1

          This is the highest percentage saving on cost

1

(b)     transferred to environment / surroundings

1

          as heat / thermal energy

1

[5]

Q16.Under the same conditions, different materials heat up and cool down at different rates.

(a)     What is meant by specific heat capacity?

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(2)

(b)     Quenching’ is a process used to change the properties of steel by cooling it rapidly.

The steel is heated to a very high temperature and then placed in a container of cold water.

(i)      A metalworker quenches a steel rod by heating it to a temperature of 900 °C before placing it in cold water. The mass of the steel rod is 20 kg.

The final temperature of the rod and water is 50 °C.

Calculate the energy transferred from the steel rod to the water.

Specific heat capacity of steel = 420 J / kg °C.

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Energy transferred = ........................................ J

(3)

(ii)     The temperature of the steel rod eventually returns to room temperature.

Compare the movement and energies of the particles in the steel rod and in the air at room temperature.

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(3)

M16.(a)     energy required to raise the temperature of a substance by 1 °C

accept heat for energy

1

unit mass / 1 kg

1

(b)     (i)      7 140 000 (J)

allow 2 marks for a correct substitution, ie

E = 20 × 420 × 850

provided no subsequent step

850 gains 1 mark if no other mark awarded

3

(ii)     particles in the air have more (kinetic) energy than the particles in the steel

allow particles in the air have a greater speed.

1

steel

particles vibrate (about fixed positions)

1

air

particles move freely

1

(ii)     the most energetic particles

accept molecules for particles throughout

accept the fastest particles

1

have enough energy to escape from (the surface of) the water

1

therefore the mean energy of the remaining particles decreases

accept speed for energy

1

as energy decreased, temperature has decreased

1

[12]

(iii)    When the steel rod is being quenched, the temperature of the water rises to 50 °C. After a few hours the water cools down to room temperature.

Some of the cooling of the water is due to evaporation.

Explain in terms of particles how evaporation causes the cooling of water.

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(4)

(Total 12 marks)

M16

have enough energy to escape from (the surface of) the water

1

therefore the mean energy of the remaining particles decreases

accept speed for energy

1

as energy decreased, temperature has decreased

1

[12]

 

 

 

 

 

 

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