The photograph below shows a coffee machine. The coffee machine uses an electric element to
1 heat water.
(a) The coffee machine has a metal case.
Why would it be dangerous for the live wire of the electric cable to
...
The photograph below shows a coffee machine. The coffee machine uses an electric element to
1 heat water.
(a) The coffee machine has a metal case.
Why would it be dangerous for the live wire of the electric cable to touch the metal case?
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(1)
(b) The power output of the coffee machine is 2.53 kW.
The mains potential difference is 230 V.
Calculate the current in the coffee machine.
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Current = ____________________ A
(3)
Aston Academy Page 2 of 71(c) The coffee machine heats water from 20 °C to 90 °C.
The power output of the coffee machine is 2.53 kW.
The specific heat capacity of water is 4200 J/kg °C.
Calculate the mass of water that the coffee machine can heat in 14 seconds.
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Mass = ____________________ kg
(5)
(Total 9 marks)
(a) Complete the sentence. Choose answers from the box.
charge potential difference power temperature time
The current through an ohmic conductor is directly proportional to the
_______________________ across the component, provided
that the _______________________ remains constant.
(2)
2
Aston Academy Page 3 of 71(b) Figure 1 shows a current − potential difference graph for a filament lamp.
Figure 1
Explain how the resistance of a filament lamp changes as the potential difference across it
increases.
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(3)
(c) Many householders are replacing their filament lamps with LED lamps which are more
energy efficient.
What does more energy efficient mean?
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(1)
Aston Academy Page 4 of 71A Light Dependent Resistor (LDR) is used to turn on an outside lamp when it gets dark.
Part of the circuit is shown in Figure 2.
Figure 2
(d) The light intensity decreases.
What happens to the potential difference across the LDR and the current in the LDR?
Potential difference ___________________________________________________
Current ____________________________________________________________
(2)
(e) What is the resistance of the LDR when the potential difference across it is 4 V?
Give a reason for your answer.
Explain your answer.
Resistance = _______________________ Ω
Reason ____________________________________________________________
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(2)
Aston Academy Page 5 of 71(f) Calculate the current through the LDR when the resistance of the LDR is 5000 Ω.
Give your answer to 2 significant figures.
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Current = _______________________ A
(4)
(Total 14 marks)
The picture shows an electric bicycle. The bicycle is usually powered using a combination of the
3 rider pedalling and an electric motor.
(a) A 36 volt battery powers the electric motor. The battery is made using individual
1.2 volt cells.
(i) Explain how a 36 volt battery can be produced using individual 1.2 volt cells.
To gain full marks, you must include a calculation in your answer.
______________________________________________________________
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(2)
(ii) The battery supplies a direct current (d.c.).
What is a direct current (d.c.)?
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(1)
Aston Academy Page 6 of 71(iii) When fully charged, the battery can deliver a current of 5 A for 2 hours. The battery is
then fully discharged.
Calculate the maximum charge that the battery stores.
Show clearly how you work out your answer and give the unit.
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Charge stored = ______________________________
(3)
(b) When powered only by the electric motor, the bicycle can carry a 90 kg rider at a maximum
speed of 6 m/s. Under these conditions, the maximum distance that the bicycle can cover
before the battery needs recharging is 32 km.
The bicycle has a mass of 30 kg.
(i) Calculate the maximum kinetic energy of the bicycle and rider when the rider is not
pedalling.
Show clearly how you work out your answer.
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Kinetic energy = ______________________________ J
(2)
(ii) The bicycle can be fitted with panniers (bags) to carry a small amount of luggage.
What effect would fitting panniers and carrying luggage have on the distance the
bicycle can cover before the battery needs recharging?
______________________________________________________________
Give a reason for your answer.
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(2)
(Total 10 marks)
Aston Academy Page 7 of 71A homeowner had a new gas boiler installed.
(a) The following information is an extract from the information booklet supplied with the boiler.
Fuel Natural Gas
Water temperature 60 °C
Energy supplied to gas boiler 8.0 kJ/s (8.0 kW)
Efficiency 0.95
4
(i) Calculate the energy transferred each second by the gas boiler to the water inside
the boiler.
Show clearly how you work out your answer.
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Energy transferred by the gas boiler each second = ___________ kJ
(2)
(ii) The energy value of the gas used in a home is measured in kilowatt-hours (kWh).
The homeowner has a pre-payment meter and pays £30 into his account. With a
pre-payment meter, gas costs 15p per kilowatt-hour.
Calculate the total number of hours that the gas boiler would operate for £30.
Show clearly how you work out your answer.
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Number of hours = _________________________
(2)
Aston Academy Page 8 of 71(b) Although the gas boiler is very efficient, some energy is wasted.
Explain what happens to the waste energy.
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(2)
(Total 6 marks)
(a) The picture shows a person using a set of electronic ‘Body Fat Scales’. When the person
stands on the scales, a small, harmless, electric current passes through the person’s body.
The scales then calculate the resistance of the person’s body and convert the resistance
into a prediction of body fat content.
(i) The scales contain two 3 V cells joined in series.
Calculate the resistance of a person’s body, if when he stands on the scales, a
current of 0.12 mA passes through his body.
1000 mA = 1 A
Show clearly how you work out your answer and give the unit.
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Resistance = _______________________________
(3)
5
Aston Academy Page 9 of 71(ii) The scales can only produce a prediction of body fat content and not an accurate
measurement.
Suggest why.
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(1)
(iii) It is recommended that the scales are not used immediately after a person has drunk
a large amount of water.
Suggest why.
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(2)
Aston Academy Page 10 of 71(b) The diagram shows how someone could get an electric shock from accidentally cutting into
an electric cable. If this happens, and a Residual Current Circuit Breaker (RCCB) is being
used, the circuit will switch off automatically.
(i) A faulty appliance or circuit can be switched off by a RCCB or a fuse.
Compare the action of a RCCB with the action of a fuse.
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(2)
(ii) The graph shows how the severity of an electric shock depends on the size of the
current and the time that the current flows through the body.
Aston Academy Page 11 of 71Using the RCCB helps prevent an electric shock seriously injuring the person using
the hedge trimmers.
Using information from both the diagram and the graph explain how.
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