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 = _______________________________
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