Energy and Efficiency Questions
Mrs Rosenquist – 13th Feb 2014

Q1.        (a)      The Sankey diagram for a low energy light bulb, known as a CFL, is shown below.

(i)      What is the useful energy output that the CFL is designed to produce?
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(1)

(ii)     What effect does the waste energy output have on the surrounding air?
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(1)

(iii)    Use the information in the diagram to calculate the efficiency of the CFL.
Use the correct equation from the Physics Equations Sheet.
Show clearly how you work out your answer.
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                                                  Efficiency = ..................................................
(2)

(iv)     CFLs contain mercury. Mercury is a poisonous substance.
It is important that old CFLs are sent for recycling and not thrown into a rubbish bin.
Suggest one reason why.
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(1)

(b)     A new type of low energy bulb uses light emitting diodes (LEDs).
Draw a ring around the correct answer in the box to complete the sentence.
LED bulbs are more efficient than CFLs. This means that LED bulbs
 
 	a smaller	 	
waste	the same	proportion of the input energy compared to CFLs.	
 	a bigger	 	

(1)

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

Apart from a higher efficiency, suggest one advantage of using an LED bulb rather than a CFL.
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(1)

(d)     At the moment, LED bulbs are much more expensive to buy than CFLs.
Which two of the following would a homeowner need to know to decide whether it would be cost-effective to replace a CFL with an equally bright LED bulb?
Tick () two boxes.

 
The number of hours each bulb lasts before needing to be replaced			
The power of each bulb in watts			
The voltage of the mains electricity supply			

(1)
(Total 8 marks)

 

Q2.          Electricity may be produced from a number of different energy resources.
(i)      Complete the table below.The first one has been done for you.
 Device	Energy
resource	Useful energy transfer
from resource	
Coal-fired power station
	
Coal	
Chemical  electrical	
Hydroelectric power station
	
Stored
water	
....................  electrical	
Solar cell in calculator
	
Sun	
....................  electrical	
Wind turbine
	
Wind	
....................  electrical	
Gas-fired power station
	
Gas	
....................  electrical	

(4)

(ii)      Give one of the five energy resources opposite, which is not classified as renewable.
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(1)

(iii)     State another non-renewable energy resource.
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(1)
(Total 6 marks)

 

Q3.          The diagram shows what happens to each 100 joules of energy from crude oil when it is used as petrol in a car.
          The widths of the arrows show exactly how much energy is transferred in each particular way.

(a)     Complete the diagram by adding the correct energy value alongside each arrow.
(3)

(b)     Calculate how efficient the car engine is at transferring the energy from petrol into useful movement.
          [Show your working].
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(2)

(c)     Two students are discussing the diagram.
          The first says that none of the energy released from the crude oil is really lost.
          The other says that all of the energy released from the crude oil is really lost.
          What do you think?
          Explain your answer as fully as you can.
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(4)
(Total 9 marks)

 

Q4.           A wood burning stove is used to heat a room.

Photograph supplied by iStockphoto/Thinkstock
 
The fire in the stove uses wood as a fuel. The fire heats the matt black metal case of the stove.
(a)     The air next to the stove is warmed by infrared radiation.
How does the design of the stove help to improve the rate of energy transfer by infrared radiation?
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(2)

(b)      Burning 1 kg of wood transfers 15 MJ of energy to the stove. The stove then transfers 13.5 MJ of energy to the room.
Calculate the efficiency of the stove.
Use the correct equation from the Physics Equations Sheet.
Show clearly how you work out your answer.
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                                         Efficiency = .................................................
(2)

(c)     Some of the energy from the burning wood is wasted as the hot gases leave the chimney and warm the air outside the house.
Name one other way energy is wasted by the stove.
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(1)

(d)     Some people heat their homes using electric heaters. Other people heat their homes using a wood burning stove.
Give two environmental advantages of using a wood burning stove to heat a home rather than heaters that use electricity generated from fossil fuels.
1 .....................................................................................................................
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2 .....................................................................................................................
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(2)

(e)     The metal case of the stove gets hot when the fire is lit.
Here is some information about the stove.
 
Mass of metal case	100 kg	
Starting temperature of metal case	20 °C	
Final temperature of metal case	70 °C	
Specific heat capacity of metal case	510 J/kg °C	

Calculate the energy required to raise the temperature of the metal case to 70 °C.
Use the correct equation from the Physics Equations Sheet.
Show clearly how you work out your answer and give the unit.
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                            Energy required = ..............................................................
(3)
(Total 10 marks)
 
Q5.          The diagram shows the label from a new freezer.

(a)     An old freezer has an energy consumption per year of 350 kWh.
          Use the equation in the box to calculate the extra cost of using the old freezer for one year compared with using a new ‘A’ rated freezer.
total cost = number of kilowatt-hours × cost per kilowatt-hour	

Assume 1 kilowatt-hour (kWh) of energy costs 12 p.
Show clearly how you work out your answer.
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Extra cost per year = £ ..............................
(2)

(b)     The price of the new freezer was reduced in a sale.
          Reducing the price reduces the payback time for replacing the old freezer from 12 years to 9 years.
Calculate, in pounds, how much the new freezer was reduced in the sale.
Show clearly how you work out your answer.
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Price reduced by = £ ........................................
(2)

(c)     An advertisement in a shop claims that:
‘Replacing an old freezer with a new ‘A’ rated freezer will benefit the environment.’
Do you agree that replacing the freezer will benefit the environment?
Answer yes or no. ..............................
Explain the reasons for your answer.
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(2)
(Total 6 marks

Q6.The Sankey diagrams show the energy transferred to the surroundings each second by three different bulbs.

(a)     The filament bulb is the least efficient of the three bulbs.
Explain what least efficient means.
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(2)

(b)     Calculate the percentage efficiency of the halogen bulb.
Use the correct equation from the Physics Equations Sheet.
Show clearly how you work out your answer.
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                                                                 Efficiency = ................................%
(2)

(c)     What effect does the wasted energy from a bulb have on the surroundings?
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(1)

(d)     Use the Sankey diagrams to give a reason why the overall cost of using an LED bulb is the lowest of the three bulbs.
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(1)

(e)     The table gives further information about each type of bulb.
 
Bulb	Cost to buy in £	Average lifespan in hours	
Filament	0.50	1000	
Halogen	2.00	2500	
LED	15.00	25000	

Use only the information in the table to answer the following questions.
(i)      Which type of bulb is the most cost-effective?
Give a reason for your answer.
Bulb ............................................................
Reason .................................................................................................
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(2)

(ii)      Sales of LED bulbs are increasing.
Suggest one reason why.
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(1)
(Total 9 marks)

 

Q7.          The diagram shows what happens to each 100 joules of energy from crude oil when it is used as petrol in a car.
The widths of the arrows show exactly how much energy is transferred in each particular way.

(a)     Complete the diagram by adding the correct energy value alongside each arrow.
(2)

(b)     Calculate how efficient the car engine is at transferring the energy from petrol into useful movement.
Show clearly how you work out your answer.
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(2)
(Total 4 marks)

 

Mark Scheme

M1.         (a)      (i)     light (energy)
this answer only
1

(ii)     raises its temperature
accept warms / heats it
accept air molecules / particles gain energy / move faster
do not accept heat
do not accept pollution
1

(iii)    
20% or 0.2
allow 1 mark for correct substitution ie  provided that no subsequent step is shown 
20 without % scores 1 mark, 20 or 0.2 with a unit scores 1 mark
2

(iv)     mercury can be recovered /reused / recycled
or
mercury (vapour) does not get into the atmosphere / environment / air
accept to stop mercury poisoning the land / getting into the food chain / water supply
accept poisonous gas for mercury (vapour)
do not accept general poisoning
cause harm to the environment is insufficient
1

(b)     a smaller
1

(c)     reaches full brightness faster
accept brighter / switches on faster accept it does not get as hot
accept it will not burn someone who touches it
accept stays cool
accept temperature does not increase as much
accept temperature only goes to 24 (°C)
accept contains no mercury
do not accept wastes less energy
1

(d)     top two boxes both ticked
The number of hours each bulb lasts before needing to be replaced.
The power of each bulb in watts.
1
[8]

M2.          (i)      gravitational or potential
do not accept stored
1
          light
credit solar
1
          kinetic or movement
credit moving
1
chemical
1

(ii)      any one from
gas
coal
1

(iii)     any one from
          oil
do not accept petrol or paraffin
          peat or turf 
nuclear
credit coal or gas if not given as answer to part (ii)
do not accept wood or fossil fuel or chemical
1
[6]

 

M3.          (a)     (   B)
(      )
(A C)
          A = B  or  A/B = 20
gains 1 mark
          but A = B = 20
gains 2 marks
          A + B + C = 100
for 1 further mark
          or C = 60
3

(b)     evidence of  or 20%/0.2 gains 1 mark
          but 25%/0.25 or figure consistent with B in part (a)
gains 2 marks
2

(c)     ideas that
“lost” energy is (also) transferred (in ways we don’t want) 
total amount of energy (before and after any transfer) remains the same
energy becomes (progressively) more spread out/less easy to transfer again
this applies to all the energy/even to the energy usefully transferred
each for 1 mark
4
[9]

 

M4.          (a)     any two from:
•        black is a good emitter of (infrared radiation)
accept heat for radiation
ignore reference to absorbing radiation
•        large surface (area)
•        matt surfaces are better emitters (than shiny surfaces)
accept matt surfaces are good emitters
ignore reference to good conductor
2

(b)     90% or 0.9(0)

allow 1 mark for correct substitution, ie
provided no subsequent step shown
an answer of 90 scores 1 mark
an answer of 90 / 0.90 with a unit scores 1 mark
2

(c)     (producing) light
allow (producing) sound
1

(d)     any two from:
•        wood is renewable
accept wood grows again / quickly
accept wood can be replanted
•        (using wood) conserves fossil fuels
accept doesn’t use fossil fuels
•        wood is carbon neutral
accept a description
cheaper / saves money is insufficient
2

(e)     E = m × c × θ
2 550 000
allow 1 mark for correct substitution
ie 100 × 510 × 50
provided no subsequent step shown
answers of 1 020 000, 3 570 000 gain 1 mark
2
joules /J
accept kJ / MJ
do not accept j
for full credit the unit and numerical answer must be consistent
1
[10]

 

M5.          (a)     £15
allow 1 mark for use of 125 (kWh)
allow 1 mark for an answer 1500
allow both marks for 1500 pence / p
allow 1 mark for correct calculation of annual cost for either freezer (£27 and £42)
2

(b)     £45
          or their (a) × 3
allow 1 mark for correct use of 3
allow 1 mark for 12 – 9 = 3
2

(c)     any two from:
the marks are for the explanation
          yes plus explanation
•        less electricity / energy needed / used
accept less energy wasted
•        less (fossil) fuels burned
accept a named fossil fuel
do not accept conserving (fossil) fuels
•        less polluting gases emitted
accept a named polluting gas / greenhouse gases / carbon emissions / reduce global warming
accept an answer in terms of nuclear fuel
eg    less nuclear fuel required (1)
       less nuclear waste (1)
2
          or no plus explanation
•        old freezer must be disposed of
•        hazardous chemicals inside freezer
accept CFC gases
•        (lot of) energy used in producing new freezer
[6]

 

M6.         (a)     highest proportion / percentage of (input) energy wasted
NB this answer gains 2 marks
allow higher / greater
allow ratio
accept for 1 mark lots of energy wasted
or
allow for 1 mark wastes most energy
2

(b)
10 % (or 0.1 if % sign crossed out)
allow 1 mark for the correct substitution into the correct equation
eg (5/50) × 100
or (1/10) × 100
allow 1 mark if 0.1 is given as the answer, but % sign is still present
2

(c)     heats it (the surroundings)
allow given off as heat
or
increases the temperature
ignore global warming
1

(d)      lowest energy input / needed / used
allow input only 2 J
1

(e)     (i)     filament (bulb)
allow 1 mark for filament bulb being chosen provided a reason is given (reason may be incorrect, but sensible eg cheapest)
1

lifespan is longest for the purchase cost
accept cost per hour is least / hours per £ is most
accept relevant calculation
1

(ii)     longest lifespan
allow lasts 25 000 hours
do not accept most cost-effective
1
[9]

M7.          (a)     energy used to refine oil... = 20J
energy ‘wasted’ = 60J
energy used to make car move = 20J
all three correct = 2 marks
two correct = 1 mark
one / none correct = 0 marks
2

(b)     25% / 0.25
for correct answer
allow error carried forward correctly from part (a)
if answer is incorrect accept evidence of 
or 20% / 0.2 for 1 mark
2
[4]