P1 Revision Booklet

Cost of electricity

Easy (Grade D/E)

Q1.          The data included in the diagrams gives the power of the electrical appliances.

TV
160 W	Radiant heater
1.0 kW	Hairdryer
1100 W	

			
Sandwich toaster
1.1 kW	Food processor
0.4 kW	Table lamp
40 W	

(a)     (i)      Which appliance is designed to transform electrical energy to light and sound?
...............................................................................................................
(1)

(ii)     Which two appliances transform energy at the same rate?
.................................................... and ....................................................
(1)

(b)     During one week, the food processor is used for a total of 3 hours.
(i)      Use the equation in the box to calculate the energy transferred, in kilowatt-hours, by the food processor in 3 hours.
 
energy transferred
(kilowatt-hour, kWh)	=	power
(kilowatt, kW)	×	time
(hour, h)	

Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
                                 Energy transferred = ................................... kWh
(2)

(ii)     Electricity costs 15 pence per kilowatt-hour.
Use the equation in the box to calculate the cost of using the food processor for 3 hours.
 
total cost    =    number of kilowatt-hours    ×    cost per kilowatt-hour	

Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
                                                      Cost = ................................... pence
(2)

(c)     A homeowner decides to monitor the amount of electrical energy used in his home.
He can do this by using an electricity meter or by using a separate electronic device.
 
Electricity meter	Electronic device	
Records to the nearest
kilowatt-hour	Records to the nearest
1/100th kilowatt-hour	

(i)      Use one word from the box to complete the following sentence.
 
precise	reliable	valid	

The reading given by the electronic device is more ........................ than the reading given by the electricity meter.
(1)

(ii)     Monitoring the electrical energy used in a home may help people to save money by encouraging them to use less electricity.
Explain why, apart from saving money, it is important for people to use less electricity.
...............................................................................................................
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(2)
(Total 9 marks)
 Q2.          Electrical appliances that are left on standby still use energy.
          The bar chart compares the average amount of ‘standby energy’ wasted each year in every home in five countries.

(i)      In which country are the homes that waste, on average, the smallest amount of ‘standby energy’?
         Draw a ring around your answer.
         Australia             France             Japan            UK               USA
(1)

(ii)     Suggest a reason why an average value is used for the ‘standby energy’ wasted in the homes.
...........................................................................................................................
...........................................................................................................................
(1)

(b)     (i)      Australia has one of the lowest electricity prices in the world.
         How does this low price seem to affect the amount of ‘standby energy’ wasted?
...........................................................................................................................
...........................................................................................................................
(1)

(ii)     In Australia, most electricity is generated in coal-burning power stations.
The Australian government wants less electricity to be wasted.
         Wasting less electricity would be good for the Australian environment.
         Explain why.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)

(c)     Energy is not usually measured in kilowatt-hours.
          Which one of the following units is usually used to measure energy?
          Draw a ring around your answer.
                                  hertz                         joule                     watt
(1)

(d)     (i)      Electricity in Japan costs the equivalent of 17 pence per kilowatt-hour.
         Use the information in the bar chart and the equation in the box to calculate how much the ‘standby energy’ used in an average Japanese home costs each year.
 
total cost = number of kilowatt-hours × cost per kilowatt-hour	

         Show clearly how you work out your answer.
         Give your answer in pence.
...........................................................................................................................
...........................................................................................................................
Cost = ........................................ pence
(3)

(ii)     In Japan, the largest proportion of electricity is generated using nuclear fuels.
         Which one of the following statements gives a good reason for using nuclear fuels to generate electricity?
         Put a tick () in the box next to your answer.
         A nuclear power station is very expensive to build.                                     
         A small amount of nuclear fuel generates a large amount of electricity.     
         It is easy to store nuclear waste safely.                                                      
(1)
(Total 10 marks)
 
Q3.          The instruction booklet for a washing machine contains the following information.
 
Wash cycle	Average power during cycle	Time taken to run cycle	
HOT	1.6 kW	2 hours	
COOL	1.1 kW	1 ¼ hours	
FAST	1.2 kW	¾ hour	

(a)     Electricity costs 15 pence per kilowatt-hour.
Calculate, in pence, the cost of using the washing machine for one HOT wash cycle.
Write down the equation you use, and then show clearly how you work out your answer.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
Cost = ...................................  pence
(2)

(b)     Why does it cost more to use the washing machine on the HOT cycle than 
on the COOL or the FAST cycle?
........................................................................................................................
........................................................................................................................
(1)
(Total 3 marks)
 Q4.          The diagram shows four electrical appliances. Each appliance is designed to transform electrical energy into one form of output energy.

Kettle	
Toaster	
Radio	
Hair straighteners	

(a)     Which one of the appliances is designed to give a different form of output energy from the other three appliances?
                    ..........................................................................................
Give a reason for your answer.
........................................................................................................................
........................................................................................................................
(2)

(b)     The power of each appliance is given in the table.
 
Appliance	Power	
Kettle	2.5 kW	
Toaster	920 W	
Radio	15 W	
Hair straighteners	75 W	

Each appliance is switched on for 5 minutes.
Which appliance transforms the most energy?
                              ..........................................................................................
(1)

(c)     The 75 watt hair straighteners are switched on for a few minutes each day.
In one year, the amount of energy transferred from the mains electricity supply to the hair straighteners is 4 kilowatt-hours.
Electricity costs 15 p per kilowatt-hour.
Use the equation in the box to calculate the yearly cost of using the hair straighteners.
 
total cost    =    number of kilowatt-hours    ×    cost per kilowatt-hour	

Show clearly how you work out your answer.
........................................................................................................................
........................................................................................................................
                                   Total cost = ............................................. pence
(2)

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

A householder always fills the electric kettle to the top, even when only enough boiling water for one small cup of coffee is required.
Explain how the householder is wasting money.
........................................................................................................................
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(3)
(Total 8 marks)
 Q5.          (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?
...............................................................................................................
                                 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)	

Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
                               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 on medium power for three hours.
 
total cost    =    number of kilowatt-hours    ×    cost per kilowatt-hour	

Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
                                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?
                                                 ..............................................................
Give a reason for your answer.
...............................................................................................................
...............................................................................................................
...............................................................................................................
(2)

(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)
Q6.          The graph shows how the energy transferred by a 2 kW electric kettle varies with the time, in hours, that the kettle is switched on.

(a)     In one week, the kettle is used for a total of 1.5 hours.
Electricity costs 15 p per kilowatt-hour.
Use the equation in the box to calculate the cost of using the kettle for the week.
 
total cost   =   number of kilowatt-hours   ×   cost per kilowatt-hour	

Show clearly how you work out your answer.
........................................................................................................................
........................................................................................................................
                                                  Cost = ............................................. p
(2)

(b)     Draw a new line on the graph to show how the energy transferred by a 1 kW kettle varies with time.
(1)
(Total 3 marks)
 Q7.         The appliances shown below transfer electrical energy to other types of energy.

(a)     The vacuum cleaner is designed to transfer electrical energy to kinetic energy.
Three more of the appliances are also designed to transfer electrical energy to kinetic energy. Which three?
Draw a ring around each correct appliance.
3

(b)     Which two of the following statements are true?
Tick () two boxes.
 
Appliances only transfer part of the energy usefully.		
The energy transferred by appliances will be destroyed.		
The energy transferred by appliances makes the surroundings warmer.		
The energy output from an appliance is bigger than the energy input.		

(2)
(Total 5 marks)
 Q8.          (a)    The bar chart shows the power of three different electric hairdryers.
    
(i)     Which one of the hairdryers, A, B or C, would transfer the most energy in 5 minutes?
 
Write the correct answer in the box.		

(1)

(ii)      A small ‘travel’ hairdryer has a power of 500 watts.
Draw a fourth bar on the bar chart to show the power of the ‘travel’ hairdryer.
(1)

(b)     A family shares the same hairdryer.
The hairdryer has a power of 1.2 kW. The hairdryer is used for a total of 2 hours each week.
(i)      Calculate how many kilowatt-hours (kWh) of energy the hairdryer transfers in 2 hours.
Use the correct equation from the Physics Equations Sheet.
Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
                  Energy transferred = .................................................. kWh
(2)

(ii)      Electricity costs 15 pence per kWh.
Calculate the cost of using the hairdryer for 2 hours.
Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
                                     Cost = .................................................. pence
(2)

(Total 6 marks)
Q9. Each letter, A, B, C, D and E, represents an energy transformation.
A   electrical to chemicalB   electrical to heatC   electrical to kineticD   electrical to lightE   electrical to sound
Match each of the following devices to the useful energy transformation that the device is designed to make.
Write the correct letter, A, B, C, D or E, in the box below each device.
Use each letter no more than once.
 
Fan	Kettle	Lamp	Radio	

(Total 4 marks)
 Q10.          (a)     The diagram shows the energy transformations produced by a television.

When the television is working, 1200 joules of energy are supplied to the television every second. The useful energy transferred by the television is 720 joules every second.
(i)      Use the equation in the box to calculate the efficiency of the television.

Show clearly how you work out your answer.
...............................................................................................................
...............................................................................................................
                                         Efficiency = ..................................................
(2)

(ii)     Use one word from the diagram to complete the following sentence.
The electrical energy that is not usefully transformed by the television is wasted as
............................................................ .
(1)

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

K    		

L    		

Which one of the televisions, J, K or L, is the most efficient?
 
Write your answer in the box.		

Give a reason for your answer.
........................................................................................................................
........................................................................................................................
(2)

(c)     A homeowner is sent an electricity bill every 3 months. The total amount of electrical energy used during one 3-month period was 800 kilowatt-hours.
Electrical energy costs 15p per kilowatt-hour.
Use the equation in the box to calculate the cost of the energy transferred from the mains electricity supply.
 
total cost    =    number of kilowatt-hours    ×    cost per kilowatt-hour	

Show clearly how you work out your answer and give the unit.
........................................................................................................................
........................................................................................................................
                                                 Cost = ..................................................
(2)
(Total 7 marks)
Cost of electricity-Mark scheme
M1.         (a)      (i)     TV
1

(ii)     hairdryer and sandwich toaster
both required either order but no others
1

(b)     (i)      1.2
allow 1 mark for correct substitution
ie 0.4 × 3 provided that no subsequent step is shown
2

(ii)     18
accept £0.18 for both marks
or
their (b)(i) × 15 correctly calculated
an answer 0.18 scores 1 mark
allow 1 mark for correct substitution
ie 1.2 or their (b)(i) × 15 provided that no subsequent step is shown
2

(c)     (i)      precise
accept any correct indication
1

(ii)     any two from:
•        less electricity needs to be generated
•        less fuels needed
accept a named fuel used in any type of power station
•        less air / atmospheric pollution
accept named pollutant eg CO2
accept reduces carbon / carbon dioxide emissions
accept reduces radioactive waste
•        (non-renewable) energy sources last longer
accept running out of fossil fuels / a named fossil fuel
•        slows global warming / greenhouse effect
do not accept stops global warming
environmentally friendly is insufficient
less pollution is insufficient
2
[9]
 M2.          (a)     (i)      France
1

(ii)     any one from:
•        different homes have different appliances(*)
•        different homes have different numbers of appliances(*)
(*) accept all homes are different
•        standby power not the same for all appliances
•        some people will switch appliances off
accept named appliances
accept people waste different amounts of energy
•        homes have different numbers of residents
•        can’t measure every (individual) home
accept any sensible suggestions
do not accept answers in terms of accurate / precise etc
1

(b)     (i)      increases amount of energy wasted
accept (encourages) people to leave appliances on (standby)
accept increases it
1

(ii)     any two from:
•        less electricity needed / generated
•        fewer power stations needed
•        less coal is burned
do not accept coal is non-renewable / running out
answers in terms of fuel stocks neutral
•        less pollutant gases produced
accept named gases
accept harmful for pollutant
accept greenhouse gases
accept reduce / slow / stop global warming
accept reduces acid rain
2

(c)     joule
1

(d)     (i)      6800
accept £68 for 3 marks an answer of 68 gains 2 marks
allow 2 marks for correct substitution ie 400 × 17
allow 1 mark for obtaining 400
answers of 7480, 4760, 12920, 4080 gain 2 marks
3

(ii)     a small . . . . . . electricity
1
[10]
 M3.         (a)     48
allow 1 mark for calculating energy as 3.2 kWh
2

(b)     largest power and longest time to run
1
[3]
 M4.          (a)     radio
radio must be chosen for reason to score
1

gives out sound
inclusion of other forms of energy negates mark
or
others give out heat / thermal energy
1

(b)     Kettle
accept 2.5 (kW)
1

(c)     60 (p)
accept £0.6(0)
allow 1 mark for correct substitution ie 4 × 15
substitution only scores if no subsequent step shown
£60 scores 1 mark
2

(d)     (bigger volume) takes more time (to boil)
accept explanation using data from graph
1

(so) more energy transferred
do not accept electricity for energy
1

(and) this costs more money
ignore references to cost of water
1
[8]
 M5.         (a)      (i)     2(.0)
accept 2000 W or 2000 watt(s)
accept answer given in table
do not accept 2000
1

(ii)     4.5
allow 1 mark for correct substitution 
ie 1.5 × 3
allow 1 mark for the answers 1.5 or 6(.0) 
2

(iii)    54or
their (a)(ii) × 12 correctly calculated
allow 1 mark for correct substitution 
ie 4.5 × 12or
their (a)(ii) × 12
allow 1 mark if correct answer is given in pounds eg £54
2

(b)     (i)     6 pm 
1

temperature starts to rise faster
only scores if 6 pm given
orgraph (line) is steeper / steepest
it refers to graph gradient or temperature
accept answers in terms of relative temperature rise
eg 5 to 6 pm 2 °C rise, 6 to 7 pm 6 °C rise
accept temperature rises sharply / rapidly / quickly
do not accept temperature starts to rise
1

(ii)     middle box ticked
1
[8]
 M6.          (a)     45(p)
accept £0.45 for both marks
allow 1 mark for correct substitution ie 3 × 15
do not award any marks if 45 is used in a subsequent calculation to obtain a final answer
2

(b)     straight line drawn from origin passing through (1,1)
line must reach 1,1 but does not need to continue beyond
1
[3]
M7.          (a)     fan
1
drill
1
washing machine
four circled including correct three scores 1 mark
five circled scores zero
1

(b)      Appliances only transfer part of the energy usefully
1
The energy transferred by appliances makes the surroundings warmer
1
[5]
 M8.          (a)     (i)     A
1
(ii)     bar drawn with correct height
ignore width of bar
1

(b)     (i)      E = P × t
2.4
allow 1 mark for correct substitution
ie 1.2 × 2
provided no subsequent step shown
2

(ii)     36 or their (b)(i) × 15 correctly calculated
or
their (b)(i) × 0.15 correctly calculated with an answer given in £
allow 1 mark for correct substitution
ie 2.4 × 15
or
their (b)(i) × 15
allow 1 mark for correct substitution
provided no subsequent step shown
an answer £0.36 gains both marks
2
[6]
 M9. Fan         C
1
Kettle      B
1
Lamp      D
1
Radio      E
1
[4]
 
M10.         (a)      (i)      0.6or60%
allow 1 mark for correct substitution ie  provided no subsequent step shown
an answer of 0.6 / 60 with a unit gains 1 mark only
an answer of 60 gains 1 mark only
2

(ii)     heat
allow thermal
1

(b)     K
reason only scores if K is chosen
1

smallest amount of wasted energy
reasons must be comparative
accept waste arrow is narrowest
orlargest amount of useful energy
accept useful arrow is widest
waste arrow is smallest is insufficient
1

(c)     12 000 por£120
to score both marks the unit must be consistent with the numerical answer
answers 12 000 and 120 gain 1 mark only
allow 1 mark for correct substitution ie 800 × 15 or 800 × 0.15
provided no subsequent step shown
2
[7]