10 Mains Electricity

208 minutes

208 marks

Q1.The diagram shows an a.c. generator.

The coil rotates about the axis shown and cuts through the magnetic field produced by the magnets.

(a) (i) A potential difference is induced between X and Y.

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

electric generator motor transformer

This effect is called the ..................................................... effect.(1)

(ii) What do the letters a.c. stand for?

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(iii) Name an instrument that could be used to measure the potential difference betweenX and Y.

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(b) Graph 1 shows the output from the a.c. generator.

Graph 1

(i) One of the axes on Graph 1 has been labelled ‘Potential difference’.

What should the other axis be labelled?

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(ii) The direction of the magnetic field is reversed.

On Graph 1, draw the output from the a.c. generator if everything else remains the same.

(2)

(iii) The output from the a.c generator is changed to be half-wave rectified.

Draw the half-wave rectified output on Graph 2.

Graph 2

(2)

(iv) State the name of a component that may be used for the half-wave rectification of a.c.

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(1)

(c) The number of turns of wire on the coil is increased. This increases the maximum induced potential difference.

State two other ways in which the maximum induced potential difference could be increased.

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(Total 11 marks)

Q2.(a) A resistor is a component that is used in an electric circuit.

(i) Describe how a student would use the circuit to take the readings necessary to determine the resistance of resistor R.

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(ii) Explain why the student should open the switch after each reading.

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(iii) In an experiment using this circuit, an ammeter reading was 0.75 A.The calculated value of the resistance of resistor R was 16 Ω.

What is the voltmeter reading?

Use the correct equation from Section C of the Physics Equations Sheet.

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Voltmeter reading = ................................ V(2)

(iv) The student told his teacher that the resistance of resistor R was 16 Ω.

The teacher explained that the resistors used could only have one of the following values of resistance.

10 Ω 12 Ω 15 Ω 18 Ω 22 Ω

Suggest which of these resistors the student had used in his experiment.

Give a reason for your answer.

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(b) The diagram shows a fuse.

Describe the action of the fuse in a circuit.

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(Total 15 marks)

Q3.The diagrams show oscilloscope traces. Three different alternating current (a.c.) electricity supplies, J, K and L, produce these traces.

In each diagram, one vertical division on the oscilloscope screen represents 2 volts.

(a) Which one of the electricity supplies, J, K or L, has the largest peak potential difference?

Write your answer, J, K or L, in the box.

(1)

(b) Calculate the value of the largest peak potential difference.

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Largest peak potential difference = ................................... V(1)

(c) The oscilloscope is now connected across a 3 V battery. The battery supplies direct current (d.c.). The settings on the oscilloscope are not changed.

On the diagram below draw the trace you would see on the oscilloscope screen.

(2)

(Total 4 marks)

Q4.(a) The diagram shows the inside of a three-pin plug.

(i) What name is given to the wire labelled S?

Draw a ring around the correct answer.

earth live neutral

(1)

(ii) What is the colour of the insulation around the wire labelled T?

Draw a ring around the correct answer.

blue brown green and yellow

(1)

(b) The plug contains a 13 amp fuse.

(i) Which one of the following is the correct circuit symbol for a fuse?

Draw a ring around the correct answer.

(1)

(ii) The diagram shows the parts of the fuse.

What would happen if a current of 20 amps passed through the 13 amp fuse?

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(c) Not all electrical appliances are earthed.

(i) Which one of the following appliances must be earthed?

Tick ( ) one box.

Table lamp

Toaster

Hair straighteners

Give a reason for your answer.

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(ii) Earthing an appliance helps to protect a person against a possible risk.

What is the risk?

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(d) The diagrams show how two lengths of mains electrical cable were joined. The individual wires have been twisted together and covered with insulating tape. This is not a safe way to join the cables.

What is the possible risk from joining the two lengths of mains electrical cable in this way?

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(e) The diagram below shows a connecting box being used to join two lengths of electrical cable. This is a safe way to join the cables.

The cable grips are important parts of the connecting box.

Explain why.

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(Total 10 marks)

Q5.(a) The diagram shows the circuit used to obtain the data needed to plot the current–potential difference graph for a filament bulb.

(i) Why is the component labelled ‘J’ included in the circuit?

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(ii) The resistance of the bulb increases as the potential difference across the bulb increases. Why?

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(iii) The bulb is at full brightness when the potential difference across the bulb is 12 V. The current through the bulb is then 3 A.

Calculate the power of the bulb when it is at full brightness and give the unit.

Use the correct equation from the Physics Equations Sheet.

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Power = ..................................................(3)

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

The table gives data about two types of light bulb people may use in their homes.

Type of light bulb

Energy efficiency

Cost of one light bulb

Average lifetime in

hours

Halogen 10% £1.95 2 000

Light Emitting Diode (LED) 32% £11.70 36 000

Both types of light bulb produce the same amount of light.

Evaluate, in terms of cost and energy efficiency, the use of the two types of light bulb.

To gain full marks you must compare both types of light bulb and conclude which light bulb would be the best to use.

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(Total 11 marks)

Q6.The picture shows an electric cooker hob. The simplified circuit diagram shows how the four heating elements connect to the mains electricity supply. The heating elements are identical.

When all four heating elements are switched on at full power the hob draws a current of 26 A from the 230 V mains electricity supply.

(a) Calculate the resistance of one heating element when the hob is switched on at full power.

Use the correct equation from the Physics Equations Sheet.

Give your answer to 2 significant figures.

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Resistance = .............................. Ω(3)

(b) The table gives the maximum current that can safely pass through copper wires of different cross-sectional area.

Cross-sectional area in mm2

Maximum safe current in amps

1.0 11.5

2.5 20.0

4.0 27.0

6.0 34.0

(i) The power sockets in a home are wired to the mains electricity supply using cables containing 2.5 mm2 copper wires. Most electrical appliances are connected to the mains electricity supply by plugging them into a standard power socket.

It would not be safe to connect the electric cooker hob to the mains electricity supply by plugging it into a standard power socket.

Why?

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(ii) Describe the structure of the cable that should be used to connect the electric cooker hob to the mains electricity supply.

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(c) Mains electricity is an alternating current supply. Batteries supply a direct current.

What is the difference between an alternating current and a direct current?

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(Total 10 marks)

Q7.(a) The diagram shows the information plate on an electric kettle. The kettle is plugged into the a.c. mains electricity supply.

230 V 2760 W

50 Hz

Use the information from the plate to answer the following questions.

(i) What is the frequency of the a.c. mains electricity supply?

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(ii) What is the power of the electric kettle?

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(b) To boil the water in the kettle, 2400 coulombs of charge pass through the heating element in 200 seconds.

Calculate the current flowing through the heating element and give the unit.

Use the correct equation from the Physics Equations Sheet.

Choose the unit from the list below.

amps volts watts

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Current = ............................................................(3)

(c) The amount of charge passing through the heating element of an electric kettle depends on the time the kettle is switched on.

What pattern links the amount of charge passing through the heating element and the time the kettle is switched on?

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(Total 7 marks)

Q8.(a) A student set up the circuit shown in the diagram. The student uses the circuit to obtain the data needed to plot a current - potential difference graph for a diode.

(i) Draw, in the boxes, the circuit symbol for a diode and the circuit symbol for a variable resistor.

Diode Variable resistor

(2)

(ii) The student made two mistakes when setting up the circuit.

What two mistakes did the student make?

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(b) After correcting the circuit, the student obtained a set of data and plotted the graph below.

Potential difference in volts

(i) At what potential difference did the diode start to conduct an electric current?

...................................................................... V(1)

(ii) Use data from the graph to calculate the resistance of the diode when the potential difference across the diode is 0.3 V.

Use the correct equation from the Physics Equations Sheet.

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Resistance = ......................... ohms(3)

(c) The diagram shows the trace produced by an alternating current (a.c.) supply on an oscilloscope.

Each horizontal division on the oscilloscope screen represents a time of 0.01s.

(i) Calculate the frequency of the a.c. supply.

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Frequency = ............................................. hertz(2)

(ii) A diode is now connected in series with the a.c. power supply.

Why does the diode cause the trace on the oscilloscope screen to change?

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(Total 12 marks)

Q9.The diagram shows the structure of a cable. The cable is part of an undersoil heating circuit inside a large greenhouse.

(a) The cable is connected to the mains electricity supply through a residual current circuit breaker (RCCB). If the cable is accidentally cut the RCCB automatically switches the circuit off.

(i) What is the frequency of the mains electricity supply in the UK?

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(ii) What happens, as the cable is cut, to cause the RCCB to switch the circuit off?

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(iii) A circuit can also be switched off by the action of a fuse.

Give one advantage of using a RCCB to switch off a circuit rather than a fuse.

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(b) The 230 volt mains electricity supply causes a current of 11 amps to flow through the cable.

(i) Calculate the amount of charge that flows through the cable when the cable is switched on for 2 hours and give the unit.

Use the correct equation from the Physics Equations Sheet.

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Charge = ..................................................(3)

(ii) Calculate the energy transferred from the cable to the soil in 2 hours.

Use the correct equation from the Physics Equations Sheet.

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Energy transferred =.................................................. J(2)

(c) The heating circuit includes a thermistor. The thermistor is buried in the soil and acts as a thermostat to control the increase in the temperature of the soil.

Describe how an increase in the temperature of the soil affects the thermistor.

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(Total 11 marks)

Q10.(a) The diagram shows the inside of an incorrectly wired three-pin plug.

(i) What two changes need to be made so that the plug is wired correctly?

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(ii) The fuse inside a plug is a safety device.

Explain what happens when too much current passes through a fuse.

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(b) Each of these pictures shows an electrical appliance being used in a bathroom.

Using the hairdryer in picture A is dangerous. However, it is safe to use the battery-operated radio in picture B.

Explain why.

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(Total 6 marks)

Q11.(a) Describe the difference between an alternating current (a.c.) and a direct current (d.c.).

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(b) The diagram shows how the electric supply cable is connected to an electric kettle.The earth wire is connected to the metal case of the kettle.

If a fault makes the metal case live, the earth wire and the fuse inside the plug protect anyone using the kettle from an electric shock.

Explain how.

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(Total 4 marks)

Q12.(a) The diagram shows the traces produced on an oscilloscope when it is connected across different electricity supplies.

Which of the traces could have been produced by the mains electricity supply?

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Give a reason for your answer.

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(b) The picture shows two adaptors being used to plug five electrical appliances into the same socket.

Explain why it is dangerous to have all five appliances switched on and working at the same time.

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(Total 4 marks)

Q13. (a) The diagram shows a piece of two-core cable and a piece of three-core cable.

(i) Which one of the wires inside a three-core cable is missing from a two-core cable?

Draw a ring around your answer.

earth wire live wire neutral wire(1)

(ii) Use a word from the box to complete the following sentence.

double extra totally

A pottery table lamp fitted with a two-core cable is safe to use because it is

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(b) The cables connecting the power sockets in a building contain wires 1.8 mm thick. The maximum current that can safely pass through these wires is 20 amps. A fuse is included in the circuit to protect the wiring.

Explain how a fuse protects the wiring of a circuit.

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(Total 5 marks)

Q14. The graph shows how the electric current through a 12 V filament bulb varies with the potential difference across the bulb.

(a) What is the meaning of the following terms?

electric current

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potential difference

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(b) The resistance of the metal filament inside the bulb increases as the potential difference across the bulb increases.

Explain why.

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(c) Use data from the graph to calculate the rate at which the filament bulb transfers energy, when the potential difference across the bulb is 6 V.

Use the correct equation from the Physics Equations Sheet.

Show clearly how you work out your answer.

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Rate of energy transfer = ................................... W(2)

(Total 7 marks)

Q15. (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

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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Resistance = .............................................................(3)

(ii) The scales can only produce a prediction of body fat content and not an accurate measurement.

Suggest why.

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(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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(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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(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.

Using 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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(Total 10 marks)

Q16. The diagram shows a helicopter being used to rescue a person from the sea.

(a) (i) The mass of the rescued person is 72 kg.

Use the equation in the box to calculate the weight of the rescued person.

weight = mass × gravitational field strength

gravitational field strength = 10 N/kg

Show clearly how you work out your answer.

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Weight = .................................................. N(2)

(ii) An electric motor is used to lift the person up to the helicopter.The motor lifts the person at a constant speed.

State the size of the force, T, in the cable.

Force T = .................................................. N(1)

(b) To lift the person up to the helicopter, the electric motor transformed 21 600 joules of energy usefully.

(i) Use a form of energy from the box to complete the following sentence.

gravitational potential heat sound

The electric motor transforms electrical energy to kinetic energy. The kinetic energy

is then transformed into useful ..................................................... energy.

(1)

(ii) It takes 50 seconds for the electric motor to lift the person up to the helicopter.

Use the equation in the box to calculate the power of the electric motor.

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

Choose the unit from the list below.

coulomb (C) hertz (Hz) watt (W)

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Power = ..................................................(3)

(Total 7 marks)

Q17.The diagram shows an electric circuit used in a dolls’ house.The switches are 2-way switches; this means that each switch has a connecting wire that can be in one of two positions.

(a) (i) With the connecting wire in each switch in the position shown in the diagram, the lamp is off. Why?

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(ii) When switched on, the lamp has a resistance of 18 Ω and draws a current of 0.5 A from the power supply.

Use the equation in the box to calculate the potential difference of the power supply used in the circuit.

potential difference = current × resistance

Show clearly how you work out your answer.

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Potential difference = .................................................. V(2)

(iii) A second, identical lamp is added to the circuit. The two lamps are joined in series.

Calculate the total resistance of the two lamps.

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Total resistance = .................................................. Ω(1)

(b) This type of circuit is also used in real houses. One of the switches is at the top of the stairs, and the other switch is at the bottom of the stairs.

What is the advantage of using this circuit to switch a lamp on or off, rather than using a more simple circuit that has only one switch?

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(c) The diagram shows an old type of metal lamp fitting.

The cable has been connected to the lamp fitting in a way that makes the lamp fitting unsafe.

(i) What is the possible risk to someone touching the lamp fitting while the lamp is switched on?

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(ii) What should be done to make this lamp fitting safe to use?

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(Total 7 marks)

Q18. The diagrams show the inside of a 13 amp plug.

(a) (i) Which one of the plugs, A, B, C or D, is correctly wired?

Write your answer, A, B, C or D, in the box.

A B

C D

The plug that is correctly wired is

(1)

(ii) What material is the outside casing of a plug made from?

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(b) An electric drill draws a current of 2 amps from the 230 volt mains electricity supply.

Use the equation in the box to calculate the power of the drill.

power = current × potential difference

Show clearly how you work out your answer.

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Power .................................................. watts(2)

(c) A householder needs to replace a damaged plug. Most replacement plugs are sold with a 13 amp fuse fitted inside. The householder thinks it would be better for shops to sell the plugs without a fuse. He could then buy either a 3 A, 5 A or 13 A fuse to fit inside the plug.

Explain an advantage of selling plugs without a fuse, rather than with a 13 amp fuse fitted.

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(Total 6 marks)

Q19. A set of lights consists of 20 lamps connected in series to the 230 V mains electricity supply.

(a) When the lights are switched on and working correctly, the current through each lamp is 0.25 A.

(i) What is the total current drawn from the mains supply?

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(ii) Use the equation in the box to calculate the charge passing through one of the lamps in 5 minutes.

charge = current × time

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

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Total charge = ..................................................(3)

(b) One of the lamps in the set is a fuse lamp. This contains a filament which melts if a fault occurs. A short time after the lights are switched on, a fault causes the filament inside the fuse lamp to melt and all the lamps go out.

The householder cannot find another fuse lamp so connects a piece of aluminium foil across the contacts inside the fuse lamp holder.When switched on, the nineteen remaining lamps work.

What the householder has done is dangerous.

Explain why.

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(Total 6 marks)

Q20.Diagram 1 shows a hairdryer.Diagram 2 shows how the heaters and fan of the hairdryer are connected to a 3-pin plug.The hairdryer does not have an earth wire.

(a) What colour is the insulation around the wire connected to the live pin inside the plug?

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(b) Why does the hairdryer not need an earth wire?

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(c) All the switches are shown in the OFF position.

(i) Which switch or switches have to be ON to make:

(1) only the fan work; ............................................................................

(2) heater 2 work? ................................................................................(2)

(ii) The heaters can only be switched on when the fan is also switched on.

Explain why.

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(d) The table shows the current drawn from the 230 volt mains electricity supply when different parts of the hairdryer are switched on.

Current in amps

Fan only 1.0

Fan and heater 1 4.4

Fan and both heaters 6.5

Use the equation in the box to calculate the maximum power of the hairdryer.

power = current × potential difference

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

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Maximum power = ............................................................(3)

(Total 9 marks)

Q21.The diagram shows a strain gauge, which is an electrical device used to monitor a changing force.

Applying a force to the gauge causes it to stretch.This makes the electrical resistance of the wire change.

(a) (i) Using the correct symbols, add to the diagram to show how a battery, an ammeter and a voltmeter can be used to find the resistance of the strain gauge drawn above.

(2)

(ii) When in use, the strain gauge is always connected to a d.c. power supply, such as a battery.

How is a d.c. (direct current) power supply different from an a.c. (alternating current) power supply?

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(b) Before any force is applied, the unstretched gauge, correctly connected to a 3.0 V battery, has a current of 0.040 A flowing through it.

(i) Use the equation in the box to calculate the resistance of the unstretched gauge.

potential difference = current × resistance

Show clearly how you work out your answer.

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Resistance = ............................................................ Ω(2)

(ii) Stretching the gauge causes the current flowing through the gauge to decrease.

What happens to the resistance of the gauge when it is stretched?

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(iii) What form of energy is stored in the gauge when a force is applied and the gauge stretches?

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(Total 7 marks)

Q22.(a) The diagram shows the inside of an incorrectly wired three-pin plug.

(i) What two changes need to be made so that the plug is wired correctly?

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(ii) Which one of the wires inside a plug is there to make an appliance with a metal case safer to use?

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(iii) The fuse inside a plug is a safety device.

Explain what happens when too much current passes through a fuse.

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(b) Each of these pictures shows an electrical appliance being used in a bathroom.

A

Using the hairdryer in picture A is dangerous. However, it is safe to use the battery-operated radio in picture B.

Explain why.

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(Total 7 marks)

Q23. An oscilloscope is connected to an alternating current (a.c.) supply.The diagram shows the trace produced on the oscilloscope screen.

Each horizontal division on the oscilloscope screen represents 0.002 s.

(a) Calculate the frequency of the alternating current supply.

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

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Frequency = ...........................................................................(3)

(b) What is the frequency of the a.c. mains electricity supply in the UK?

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(Total 4 marks)

Q24. A homeowner has installed electric underfloor heating in the kitchen. When the heating is switched on, an electric current flows through wires running under the tiled floor surface.

(a) What is an electric current?

........................................................................................................................(1)

(b) The graph shows how the power output of an underfloor heating system depends on the area of the floor that is heated.

The area of the homeowner’s kitchen floor is 9.0 m2.

Use the graph and the equation in the box to calculate the current drawn from the 230 V mains supply by the heating system.

power = current × potential difference

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

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

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

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

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

Current = ....................................................................(4)

(Total 5 marks)

Q25. (a) The diagram shows a three-pin plug and electrical cable.

Name a suitable material to make:

the plug casing .................................................................

the inner cores of the cable. ..............................................

Give the reason for your choice of each material.

plug casing .....................................................................................................

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

inner core of the cable ...................................................................................

........................................................................................................................(4)

(b) The pictures show mains electricity being used to operate various devices.Some of the pictures show the electricity being used in a dangerous way.

In the box underneath each picture put:

a tick ( ) if the electricity is being used safely

a cross ( ) if the electricity is being used dangerously.(2)

(Total 6 marks)

Q26. (a) Look at the electrical safety information poster.

(i) Complete the table to show which size fuse, 3 A or 13 A, should be fitted to each of the appliances.

Appliance Power Fuse

Kettle 2200 W

Hair straighteners 75 W

Coffee maker 1260 W

(2)

(ii) The plug of a washing machine has been wrongly fitted with a 3 A fuse.Explain why the washing machine stops working shortly after it is switched on.

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

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

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

...............................................................................................................(2)

(b) The diagram shows a hairdryer. The cable connecting the hairdryer to the plug does not have an earth wire.

(i) Why does the hairdryer not need a cable with an earth wire?

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

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

...............................................................................................................(1)

(ii) The hairdryer takes a current of 5 A from the 230 V mains electricity supply.

Calculate the power of the hairdryer.

Write down the equation you use, and then show clearly how you work out your answer.

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

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

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

Power = ................................. W(2)

(Total 7 marks)

Q27. In the UK mains electricity is a 230 volt a.c. supply.

(a) What is the frequency of the a.c. mains electricity in the UK?

........................................................................................................................(1)

(b) (i) What is an electric current?

...............................................................................................................(1)

(ii) Explain the difference between an a.c. (alternating current) electricity supply and ad.c. (direct current) electricity supply.

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

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

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

...............................................................................................................(2)

(c) A householder has a 10.8 kW electric shower installed in the bathroom.

(i) Calculate the current drawn from the mains electricity supply by the shower.

Write down the equation you use, and then show clearly how you work out your answer.

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

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

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

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

Current = .................................... A(2)

(ii) The table gives the maximum current that can safely pass through electric cables of different cross-sectional area.

Cross-sectionalarea

in mm 2

Maximum safecurrentin amps

1.0 11.5

2.5 20.0

4.0 27.0

6.0 34.0

10.0 46.0

16.0 62.0

The existing power sockets in the house are wired to the mains electricity supply

using 2.5 mm2 cable.

Use the data in the table to explain why the shower must not be connected to the mains electricity supply using 2.5 mm2 cable.

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

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

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

...............................................................................................................(2)

(iii) The circuit connecting the shower to the mains electricity supply must include a residual current circuit breaker (RCCB) and not a fuse.

Give two advantages of using a RCCB to protect a circuit rather than a fuse.

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

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

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

...............................................................................................................(2)

(Total 10 marks)

M1.(a) (i) generator1

(ii) alternating current1

(iii) voltmeter / CRO / oscilloscope / cathode ray oscilloscope1

(b) (i) time1

(ii) peaks and troughs in opposite directions1

amplitude remains constantdependent on first marking point

1

(iii) wave modified to omit all values above or below x-axis1

same amplitude and wavelength as originaldependent on first marking point

1

(iv) diode1

(c) any two from:

• increase speed of coil• strengthen magnetic field• increase area of coil

do not accept larger2

[11]

M2.(a) (i) any six from:

• switch on• read both ammeter and voltmeter

allow read the meters• adjust variable resistor to change the current• take further readings• draw graph• (of) V against I

allow take mean• R = V / I

allow take the gradient of the graph6

(ii) resistor would get hot if current left on1

so its resistance would increase1

(iii) 12 (V)0.75 × 16 gains 1 mark

2

(iv) 15 (Ω)1

16 is nearer to that value than any other1

(b) if current is above 5 A / value of fuse1

fuse melts

allow blows / breaksdo not accept exploded

1

breaks circuit1

[15]

M3.(a) L1

(b) 6 (V)1

(c) horizontal line drawn1

drawn in correct positionjudge by eye

1[4]

M4.(a) (i) neutral1

(ii) brown1

(b) (i) centre symbol ringed

accept any correct indication

1

(ii) fuse (wire) meltsaccept fuse blowsaccept fuse breaks / snapsaccept burns out appliance doesn’t work is insufficientoverheat is insufficientdo not accept blows up

1

(c) (i) Toaster1

(only one with) a metal case / outsidereason only scores if toaster chosenaccept it is metal accept outside / case / metal conducts (electricity)do not accept it conducts electricity

1

(ii) electric shock / electrocution

do not accept explosion1

(d) overheating of cables or fireit refers to the electric cableaccept short circuit / sparkingoverheating of tape is insufficientdo not accept electrocution / shock

1

(e) stop cable(s) being pulled loose / freeaccept wire(s) for cable(s) accept to hold cables in place

1

and so breaking the circuit or and shorting (one wire to another)or and causing a fire risk / sparking

accept appliance / plug would not work1

[10]

M5.(a) (i) to obtain a range of p.d. valuesaccept increase / decrease current / p.d. / voltage / resistanceaccept to change / control the current / p.d. / voltage / resistanceto provide resistance is insufficienta variable resistor is insufficientdo not accept electricity for current

1

(ii) temperature of the bulb increasesaccept bulb gets hot(ter)accept answers correctlyexpressed in terms of collisions between (free) electrons and ions / atomsbulb gets brighter is insufficient

1

(iii) 36allow 1 mark for correct substitution, ie 12 × 3 provided no subsequent step shown

2

watt(s) / Waccept joules per second / J/sdo not accept w

1

(b) 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 refer to the information in the Marking guidance, and apply a ‘best-fit’ approach to the marking.

0 marksNo relevant content.

Level 1 (1-2 marks)There is a basic comparison of either a cost aspect or an energy efficiency aspect.

Level 2 (3-4 marks)There is a clear comparison of either the cost aspect or energy efficiency aspectORa basic comparison of both cost and energy efficiency aspects.

Level 3 (5-6 marks)There is a detailed comparison of both the cost aspect and the energy efficiency aspect.

For full marks the comparisons made should support a conclusion as to which type of bulb is preferable.

Examples of the points made in the response:

cost

• halogen are cheaper to buysimply giving cost figures is insufficient

• 6 halogen lamps cost the same as one LED

• LEDs last longer

• need to buy 18 / more halogen lamps to last the same time as one LED

• 18 halogens cost £35.10

• costs more to run a halogen than LED

• LED has lower maintenance cost (where many used, eg large departmental store lighting)

energy efficiency

• LED works using a smaller current

• LED wastes less energy

• LEDs are more efficient

• LED is 22% more energy efficient

• LED produces less heat

• LED requires smaller input (power) for same output (power)6

[11]

M6.(a) 35an answer with more than 2 sig figs that rounds to 35 gains 2marks

allow 2 marks for correct method, ie

allow 1 mark for I = 6.5 (A) or R = an answer 8.8 gains 2 marksan answer with more than 2 sig figs that rounds to 8.8 gains 1mark

3

(b) (i) (maximum) current exceeds maximum safe current for a 2.5 mm2 wireaccept power exceeds maximum safe power for a 2.5 mm2 wire

or(maximum) current exceeds 20 (A)

(maximum) current = 26 (A) is insufficient1

a 2.5 mm2 wire would overheat / meltaccept socket for wiredo not accept plug for wire

1

(ii) (contains) live, neutral and earth wiresaccept is a three-core cable

1

cross-sectional area of (live and neutral) wire(s) (minimum of) 4 mm2

accept 6 mm2 for 4 mm2

1

wire / cable should be insulatedaccept a suitable named insulator, eg PVC / rubber / plastic

1

(c) a.c. is constantly changing directionaccept a.c. flows in two directionsaccept a.c. changes directiona.c. travels in different directions is insufficient

1

d.c. flows in one direction only1

[10]

M7.(a) (i) 50 (Hz)1

(ii) 2760 (W)1

(b) 12

allow 1 mark for correct substitution, ie 2400/200orallow 1 mark for 2760/230 provided no subsequent step shown

2

amps1

(c) the charge is directly proportional to the time switched on foraccept for 1 mark the longer time (to boil), the greater amount of chargeor positive correlationor they are proportional

2[7]

M8.(a) (i) symbol for a diode

accept 1

symbol for a variable resistor 1

(ii) voltmeter is in series or voltmeter is not in parallel1

ammeter is in parallel or ammeter is not in seriesaccept an answer in terms of how the circuit should be correctedvoltmeter and ammeter are wrong way around is insufficient

1

(b) (i) 0.2 (V)accept any value between 0.20 and 0.21 inclusive

1

(ii) 37.5allow 1 mark for I = 0.008 or allow 2 marks for correct substitution, ie 0.3 = 0.008 × R or allow 1 mark for a correct substitution using I = 0.8 or I = 0.08or I = 0.009 or allow 2 marks for answers of 0.375 or 3.75 or 33(.3)

3

(c) (i) 25

allow 1 mark for obtaining period = 0.04(s)2

(ii) diode has large resistance in reverse / one direction1

so stops current flow in that / one directionallow diodes only let current flow one way / directionallow 1 mark for the diode has half-rectified the (a.c. power) supply

1[12]

M9.(a) (i) 50(Hz)ignore any unit given

1

(ii) any two from:

• (some) current flows to Earthaccept ground for Earth

• current flows through copper braidaccept current flows through the earth wireaccept electricity for current in either the first or second marking point but not both

• RCCB detects difference between current in live and neutral wire2

(iii) can be resetaccept does not need replacing

or

faster actingaccept switches circuit off faster

1

(b) (i) 79 200

allow 1 mark for correct substitution, ie 11 = an answer 22 gains 1 mark

2

coulombs / Cdo not accept c

1

(ii) 18 216 000accept for 2 marks 18 216 kJ or 18.216 MJ

or

230 × their (b)(i) correctly calculatedallow 1 mark for correct substitution, ie 230 × their (b)(i) or allow 1 mark for power calculated as 2530(W)

2

(c) increases temperature of thermistor1

changes resistance (of thermistor)do not accept increases resistance (of thermistor)an answer decreases resistance (of thermistor) gains 2 marks

1[11]

M10.(a) (i) connect the earth wire (to pin)answers must be in terms of correcting the faults

1

screw cable grip (across cable)accept tighten the cable grip

1

(ii) any two from:

• fuse gets (very) hot• fuse melts

accept blows for meltsdo not accept break / snap fuse / blow up

• circuit breaks / switches offaccept stops current flowing

2

(b) any two from:

• hairdryer is plugged into mains (electricity socket)it refers to hairdryer hairdryer works from the mains

orhairdryer is using 230 V

accept 240 for 230

• water conducts electricitydo not accept water and electricity don’t mix

• radio is low power / current / pd / voltageaccept radio not connected to the mains do not accept radio is waterproof

• (the current in / pd across) hairdryer more likely to give a (fatal) electric shockaccept the idea of electrocution if hairdryer is wet

accept the idea of radio not causing electrocution if wet2

[6]

M11.(a) d.c. flows in (only) one direction1

a.c. changes direction (twice every cycle)accept a.c. constantly changing directionignore references to frequency

1

(b) a current flows through from the live wire / metal case to the earth wireaccept a current flows from live to earthdo not accept on its own if the current is too high

1

this current causes the fuse to meltaccept blow for meltdo not accept break / snap / blow up for melt

1[4]

M12. (a) Aonly scores if A chosen

1

it is alternating / a.c.accept because B and C are d.c.

orit changes direction/p.d.

accept voltage for p.d.it goes up and down is insufficientit is constantly changing is insufficientan answer B and/or C with the reason because it is direct current/d.c scores 1 mark

1

(b) too much current (through socket)accept electricity for currentaccept too much poweraccept socket/circuit overloadeddo not accept voltage/p.d for current

1

wiring / socket gets hotaccept melts for gets hotaccept risk of firerisk of fire in appliances is insufficientignore reference to sparking

overloaded plugs and plugs getting hot or fuses melting is insufficient

1[4]

M13. (a) (i) earth wire1

(ii) double1

(b) if too much current flows through the wireaccept power for currentdo not accept electricity for currentaccept if more than 20 amps flows through the wire

1

the fuse (overheats and) meltsaccept ‘blows’ for meltsdo not accept explodes / breaks / snaps etc

1

breaking the circuitaccept stopping the current flow

1[5]

M14. (a) electric current(rate of) flow of (electric) charge / electrons

accept with Q and t correctly named

1

potential differencework done / energy transferred per coulomb of charge (that passes between two points in a circuit)

accept with W and Q correctly named

1

(b) metals contain free electrons (and ions)accept mobile for free

1

as temperature of filament increases ions vibrate faster / with a bigger amplitude

accept atoms for ionsaccept ions/atoms gain energyaccept vibrate more for vibrate fasterdo not accept start to vibrate

1

electrons collide more (frequently) with the ionsor(drift) velocity of electrons decreases

do not accept start to collideaccept increasing the p.d. increases the temperature (1 mark)and(and) resistance increases with temperature (1 mark) if no other marks scored

1

(c) 7.8allow 1 mark for obtaining value 1.3 from graphor allow 1 mark for a correct calculation using an incorrect current in the range 1.2-1.6 inclusive

2[7]

M15. (a) (i) 50 000allow 1 mark for correct substitution, ie6 = 0.00012 × Ror 6 = 0.12 × Ror answers of 25 000 or 50 gain 1 markor allow 1 mark for an incorrect answer caused by one error only ie using 3V or an incorrect conversion of current

2

ohm / Ωan answer 50kΩ gains 3 marks

1

(ii) (body) resistance changes

or

body fat/resistance affected by (many) factorsaccept named factor, eg age, gender, height, fitness, bone structure, muscle, drinking water related to body fat / resistance

1

(iii) gives misleading / wrong/inaccurate valuedo not credit if specifically linked to a change in mass / weight

1

(because) high water content changes body resistanceaccept a specific change to resistancewater changes body mass is insufficient

1

(b) (i) RCCB – detects difference between current in live and neutral (wires)accept RCCB can be reset

1

fuse – (overheats and) meltsaccept blows for melts

1

(ii) switches the circuit / hedge trimmers off within 60 millisecondsallow for 1 mark the RCCB / it is (very) fast.do not accept the bigger the current the faster the RCCB switches off

2[10]

M16. (a) (i) 720allow 1 mark for correct substitution,ie 72 × 10 provided no subsequent step shown

2

(ii) 720ortheir (a)(i)

1

(b) (i) gravitational potentialallow gravitationalallow potential

1

(ii) 432

allow 1 mark for correct substitution, ie provided no subsequent step shown

2

watt / W1

[7]

M17. (a) (i) circuit not completeaccept circuit is brokenaccept switch / s are open / off

1

(ii) 9allow 1 mark for correct substitution, ie 0.5 × 18 provided no subsequent step shown

2

(iii) 361

(b) can be switched on / off from top or bottom of stairs1

(c) (i) (electric) shockaccept fitting becomes liveaccept answers giving a possible consequence of electric shock, eg death

1

(ii) connect the earth wire1

[7]

M18. (a) (i) D1

(ii) plastic or rubberaccept a specific type of plasticaccept electrical insulator

1

(b) 460allow 1 mark for correct substitution ie 2 × 230

2

(c) any two from:

• not all appliances need a 13 A fuseidea that 13 A is (much) bigger than required by many appliancesdo not accept some appliances require more than 13 A

do not accept 13 A fuse will blow

• can choose the most suitable fuse (for the appliance)accept install correct fuse for the appliance

• (in the event of a fault) 13 A fuse may allow too much current to flow through an applianceorfuse may not melt (before appliance is damaged)

• may already have the fuseidea of reusing a fusedo not accept cheaper unless explained correctly

2[6]

M19. (a) (i) 0.25 (A)1

(ii) 75allow 1 mark for converting 5 minutes to 300 secondsor allow 1 mark for correct substitutionie 0.25 × 300allow 1 mark for an answer 1.25allow 1 mark only for their (a)(i) × 300 correctly calculated

2

coulombs or Cdo not accept c

1

(b) any two from:

• fault not repairedaccept if a fault was to occur

• larger current will (still) flow

• aluminium foil will not melt (if a fault)accept aluminium foil needs a higher current / charge to melt

• wiring will overheat / (may) cause a fireaccept idea of fire hazarddo not accept explode etc

2[6]

M20. (a) brown1

(b) outside / case is plastic / an insulatoraccept is double insulatedaccept non-conductor for plasticdo not accept it / hairdryer is plastic

1

(c) (i) (1) S1

and no other1

(2) S1 and S3

both required, either order1

(ii) S1 must be ON (for either heater to work)do not accept reference to ‘fan’ switch

1

S1 switches the fan on1

(d) 1495allow 1 mark for correct substitutionie, 6.5 × 230

2

watt(s) or Wan answer of 1.495 kW gains 3 marksalthough the unit is an independent mark for full creditthe unit and numerical value must be consistentaccept joules per second or J/s

1[9]

M21. (a) (i) ammeter and battery in series with the gaugesymbols must be correctignore a voltmeter drawn in series

or cells reversed to cancel out1

voltmeter in parallel with the gaugesymbol must be correctaccept a freestanding circuitdiagram provided strain gauge is labelled or a resistor symbol used for the strain gauge

1

(ii) d.c. flows only in one directiona.c. changes direction is insufficient

1

(b) (i) 75this answer onlyallow 1 mark for correct substitution and transformation,

ie resistance = 2

(ii) increases1

(iii) elastic / strain potentialdo not accept potential

1[7]

M22. (a) (i) connect the earth wire (to pin)

answers must be in terms of correcting the faults1

screw cable grip (across cable)accept tighten the cable grip

1

(ii) earth (wire)accept the green and yellow (wire)

1

(iii) any two from:

• fuse gets (very) hot

• fuse meltsaccept blows for meltsdo not accept break / snap fuse / blow up

• circuit breaks/ switches offaccept stops current flowing

2

(b) any two from:it refers to hairdryer

• hairdryer is plugged into mains (electricity socket)hairdryer works from the mains

or hairdryer is using 230 V

accept 240 for 230

• water conducts electricitydo not accept water and electricity don't mix

• radio is low power / current / pd / voltageaccept radio not connected to the mainsdo not accept radio is waterproof

• (the current in / p.d.across) hairdryer more likely to give a (fatal) electric shockaccept the idea of electrocution if hairdryer is wetaccept the idea of radio not causing electrocutionif wet

2[7]

M23. (a) 125allow 1 mark for obtaining time period = 0.008 (s)

orfrequency = 1 / time period (or their calculated time period)

2

hertzorHz

do not accept hz1

(b) 50 (hertz)1

[4]

M24. (a) (rate of) flow of charge / electrons / ionsaccept movement for flowdo not accept flow of electricity

1

(b) 7(.0)accept 6.96 / 6.95 or an answer that would approximate to 6.96 if roundedallow 1 mark for obtaining correct power and changing to watts ie 1600orallow 2 marks for correct substitution and transformationie 1600 ÷ 230an answer 0.00696 / 0.007 gains 2 marksallow 1 mark for 1.6 / 230 or 1.7 / 230an answer 7.39 or 7.4 gains 2 marks

3

amp (ere)accept A

1[5]

M25. (a) plasticaccept rubber

1

as it is a good electrical insulatoraccept as it is a poor electrical conductorany mention of heat negates this mark

1

copper1

as it is a good electrical conductorany mention of heat negates this mark

1

(b) all ticks and crosses in the correct places

A –

B –

C –

D – allow 1 mark for 3 correct

2[6]

M26. (a) (i) all 3 correct

kettle 13 A

hair straighteners 3 A

coffee maker 13 Aallow 1 mark for 2 correct

2

(ii) fuse will(get hot and) melt

allow blow for meltdo not accept snap / break

1

causing the circuit to be broken1

(b) (i) the hairdryer is double insulatedaccept has a plastic cover

1

(ii) 1150allow 1 mark for substitution into correct equationie 5 × 230allow both marks for 1.15

provided the unit is changed to kW2

[7]

M27. (a) 50 hertz1

(b) (i) a flow of charge / electrons1

(ii) a.c. is constantly changing direction1

whilst d.c. always flows in the same direction1

(c) (i) 46.9accept 47.0allow 1 mark for correct transformation and substitution

ie 2

(ii) current (46.9 A) exceeds maximum safe current for2.5 mm2 cable

accept cable needs to be 16.0 mm2

1

therefore if a 2.5 mm2 cable were used it would overheat / meltcable needs to be 10.0 mm2 limits maximum credit to 1 mark

1

(iii) can be reset1

disconnects circuit faster (than a fuse)1

[10]

E3.(a) The vast majority of students were able to identify ‘L’ as the supply with the largest peak potential difference.

(b) This question was poorly answered. A minority of students gave the correct answer of 6,

the most common incorrect answer being 12 from measuring from trough to peak on the oscilloscope trace although answers were given in a range from 0 to 256.

(c) This question was poorly answered, the vast majority of students incorrectly choosing to draw waves. Less than 10% of students scored both marks.

E4.(a) (i) Half of the students scored this mark.

(ii) This was better known with a majority of students giving the correct answer.

(b) (i) A majority of students were able to identify the circuit symbol for a fuse.

(ii) A majority of students answered this question correctly, with most of the incorrect responses being in terms of the fuse blowing up or exploding, or statements regarding the shattering of the glass or metal caps.

(c) (i) Although most students correctly identified the toaster as the appliance needing an earth wire, the second mark was harder to achieve as a significant number of students thought that the metal casing was present due to heat considerations.

(ii) Most students answered correctly that an electric shock or electrocution would be the possible risk from the appliance, the most common incorrect response involved overheating and subsequent burns to a person.

(d) Few students were aware that the inappropriate connection of the wires would cause sparking and heating of the wires. There were many vague responses solely in terms of the overheating of the tapes or the possibility of electrocution.

(e) A majority of the students explained how the use of a connecting box could be a secure way to join two lengths of electrical cable but there were very few correct answers that gained both marks by continuing the answer to explain why this was important.

E5.(a) (i) This was very poorly answered with few students realising what the function of ‘J’ was in the circuit. A significant number of students did identify ‘J’ as a variable resistor but did not go on to say what it does.

(ii) Again very poorly answered with only a very small minority of students understanding that the resistance increases as the temperature of the bulb increases.

(iii) Again the calculation was well done with nearly three quarters of students giving the correct numerical answer. However the unit was not well known with only just over one fifth of students giving the correct one.

(b) Most students managed to score some marks on this question with the majority of students at level 2 and gaining 3 or 4 marks. Comparison of the cost aspect was done best by students, with many correctly calculating the need for 18 halogen bulbs to last as long as 1 LED and the higher associated costs. Very few students made a comment on efficiency beyond the fact that LEDs were more efficient. A lot could have been written about energy efficiency such as less waste energy, less heat produced, lower power input and lower running costs for the LED bulb. Even a simple statement of not having to change the LED bulb as often as the halogen bulb was not common. There were a small number of students who believed that you could increase the efficiency by adding more bulbs. So for example if you had 4 halogen bulbs at 10% efficiency then this would give you 40% efficiency. This led to erroneous conclusions that you could make halogen bulbs

more efficient than an LED bulb. There were also a small number of students who believed that the higher the number for efficiency the more energy was wasted and so a higher efficiency was undesirable. A large number of students wasted time, and a considerable amount of the answer space, just rewriting the information in the table without any comparison other than to quote the numbers given. Specialist terms were usually limited to those given in the question. There was a considerable variation in the ability to use good English; some excellent sentences and clear writing, and at the other extreme an inability even to use capital letters and full stops, and copy correct spellings from words given in the question.

E6.(a) The correct answer of 35 was rarely given; 8.8 as the resistance for all 4 heating elements was the most common answer. A number of students then incorrectly divided by 4 to find the resistance of a single heating element. These students usually gained a single mark for dividing the p.d. of 230 V by the current of 26 A. The concept of significant figures is still not well understood with very few students scoring full marks.

(b) (i) Very few students scored both marks, however half of students did score one mark. Most answers lacked detail and some made reference to potential difference rather than current. Several students confused current and p.d, writing that 230 V was too high for the wire. Surprisingly few students scored the mark for overheating with many references to plugs / things blowing up and fuses melting rather than the wire.

(ii) A significant minority of students did not attempt this part question. Many students referred to a plug rather than the cable. Some answers suggested that students were not familiar with what a cable was, except in the context of a ‘cable grip’ in the plug, which made them believe it was the plug that they needed to describe. Very few students scored all three marks, and half of students only scored one mark. The idea of the wires connecting to the pins of a plug was quite common, as were a variety of colours.

(c) Nearly half of students gained both marks. For direct current, frequent incorrect answers included: ‘the current goes straight to the device’, or ‘straight to the source with no wires’, ‘direct current travels in straight lines’. With regard to alternating current incorrect answers seen frequently included ‘alternating current goes up and down’, ‘only flows in a parallel circuit’ or ‘goes in many directions.’

E7.(a) (i) Only half of the students were able to select the correct value for frequency.

(ii) Most students could identify the power correctly.

(b) The majority of students were able to score two marks by selecting the correct equation and calculating the current. However, only a third of students gave the correct unit. Many students failed to either write a unit in the answer space or indicate a choice by circling one of the units in the list.

(c) Two thirds of students gained one mark by giving a correct pattern linking the time and charge. However very few went on to score both marks by stating that the relationship between the variables was directly proportional.

E8.(a) (i) Considering this question was asking for recall of standard symbols it is surprising and disappointing that over half of the students scored zero. Only a small minority of the students gained both marks. The variable resistor caused fewer problems than the diode.

(ii) Again poorly answered with only about a third of the students gaining both marks and just less than half of the students scoring zero. Many of the students mentioned the switch and the direction of the diode as a reason for the circuit being incorrect. Others showed even less understanding of the circuit.

(b) (i) The majority of the students gained this mark.

(ii) Just over half of the students got this question correct gaining the full three marks. A Significant number of students made errors by taking the numbers 0.08, 0.8 or 0.009 from the graph.

(c) (i) Just less than a quarter of students managed to achieve two marks on this question; with a further small number gaining one mark by obtaining the period, with a significant number believing this was the final answer.

(ii) Very few students achieved both marks on this question – most made no mention of high resistance in the reverse direction. Less than half of the students achieved the second marking point with reference to current flowing only in one direction.

E9.(a) (i) This was poorly answered with about a 50/50 split between the numbers 50 and 230.

(ii) Just over three quarters of the students failed to score any marks often confusing RCCBs saying they switched off the circuit when the (live) current was too high. Others thought that they worked like fuses with something in them melting at too high a current. Of the minority who scored one mark it was usually obtained by correctly stating that the current in the live and neutral wires differed, but then went on to describe the mechanics of how the device worked rather than giving a reason for the currents being different. The very few who achieved both marks obtained these by linking the current flowing to ground through the earth wire/copper braid but omitted the way the RCCB detected the fault.

(iii) The majority of students scored this mark for the idea of quicker operation or the ability to reset / reuse RCCBs. Some students gave insufficient detail with answers such as ‘automatic operation’ or ‘safer’ with little exemplification.

(b) (i) Since the equation for this is given it was disappointing how few students managed to use the equation, transform it correctly or substitute values in correctly. Approximately half the students either did not manage to correctly change hours to seconds or did not realise this had to be done.

(ii) A minority scored both marks on this and very few scored one mark – if students found the correct equation they could put the values in and do the arithmetic. Unfortunately too many students chose the incorrect equation trying to use E = P × t and using p.d. for power rather than E = V × Q. Some students tried to use E = V × I × t but again incorrectly converted hours to seconds. However it was pleasing to see that most students showed the working they used towards getting their answer even though it was often wrong.

(c) Most students did not appreciate that the thermistor increased in temperature but related the answer to heating the ground. The link between the thermistor and a decrease in resistance was well understood. Weaker students did not understand the way in which a thermistor works or the effect of temperature on its resistance.

E10.(a) (i) The majority of students gained both marks. Some students wrote what was wrong

with the plug rather than what changes should be made to the plug. Even so, these students were able to gain one mark.

(ii) The majority of students were able to gain one mark for the idea of the fuse overheating / melting. Few students gave both points in order to gain both marks. Many students scored zero because they used imprecise / incorrect ideas, e.g. the fuse would ‘blow up’ or ‘snap’.

(b) This was not well answered with few students gaining both marks. One mark was often gained by stating that the hairdryer was connected to the mains electricity / 230 volts. Answers for the radio were often written in terms of the radio being fixed to the wall or the radio not using electricity.

E11.(a) This was disappointingly completed for a simple piece of recall. A small number of the students scored both marks and a small number scored one mark. Common errors where one mark was scored indicated that direct current flowed in one direction but alternating could go ‘in any direction’. Many other incorrect responses referred to oscilloscope traces, ‘positive’ and ‘negative’ and frequency.

(b) A very small number of the students gained both marks and only a small number scored one mark. The main error was for students to recall complete statements about the manner in which a fuse melts with no reference to the kettle. The earth connection was often described as an active component ‘pushing current’, ‘redirecting energy’ and undertaking other functions which indicated a complete lack of understanding.

E12. (a) Just over 60% of students chose A. However of these only 11% could give a correct reason why. The majority of answers were in terms of the trace showing the supply to be continually switched on and off.

(b) A lot of students seemed to get confused between a socket and a plug and did not use terminology correctly. A significant number of students seem to be under the impression that a fuse melting would automatically lead to a fire. Most students rather than focusing on the current drawn through the wiring / socket being too high and making the wiring / socket too hot, would say that the appliances or plugs would get hot. Where it was mentioned, the connection between a high current and overheating seemed to get lost within the descriptions.

E13. (a) (i) Although two-thirds of students scored this mark, it is perhaps surprising that more did not know that the two-core cable does not include an earth wire.

(ii) Nearly two-thirds of students understood that the lamp was double insulated. The most popular incorrect answer was ‘totally’ insulated.

(b) This question was not answered well with few students scoring the maximum three marks available. Many incorrect responses assumed that a fuse contributed to the protection of the wiring of a circuit inside a building by providing some kind of enhancement to the

electrical insulation of a cable, or improvement to the physical fixing of wires inside a socket. There was also the erroneous assumption that the thin wire of a fuse mechanically snaps rather than overheats and melts.

E14. (a) Only just over half of students were able to give an acceptable meaning for electric current. There were many vague answers such as ‘the flow of electricity‘. Very few students, were able to give the meaning of potential difference. Common errors often included the idea of a force pushing the electricity around.

(b) This question was poorly answered. Very few students referred to free electrons at all. Most students gained one mark for an answer linking the increasing p.d. to the temperature however, few went on to then link this to the resistance increase. A significant number of students thought that the resistance caused the p.d. Those students who tried to explain resistance in terms of electrons colliding more often as the ions vibrate faster found it difficult to express themselves clearly. Many students had ‘start’ to vibrate and ‘start’ to collide, implying this was not happening before. Others had ions moving, rather than vibrating. Some students linked resistance to it being harder for electrons to pass, without giving any explanation why.

(c) About half the students scored both marks. The most common error was to misread the graph scale when obtaining the current at 6 volts. However, students that did misread the graph could still score one mark by showing a correct calculation using their incorrect value.

E15. (a) (i) This question was poorly answered with only a third of students completing the calculation correctly. Many students missed the information that the scales contained two cells and so used 3 V in the calculation. A large number of students were unable to convert mA to A. Some students chose the correct equation, but were unable to transpose it correctly. It was extremely disappointing that only a tenth of students were able to give the unit for resistance.

(ii) This question was poorly answered by most students. Many students made reference to other tissues, such as muscle, but were unable to relate this to changes in body fat or body resistance. Common errors included responses relating to clothing and responses in terms of the inaccuracy of the apparatus or lack of precision.

(iii) A small number of students correctly identified the water would cause a change in body resistance and so give misleading values. Many students however, took this idea further and suggested a risk of electrocution or internal burns because water was a good conductor. A significant number of students simply stated that you would

weigh more because you had drunk the water.

(b) (i) Very few students were able to write that the RCCB works by detecting a difference between the current in the live wire and the current in the neutral wire. However, many students were able to score this mark by giving the alternative answer that the RCCB could be reset. A small number of students were under the impression that an RCCB is a type of fuse or that it contains a fuse inside. Over half of students were able to score a mark by stating that the fuse melts / blows. However, students should be aware that other descriptions such as, breaks, explodes, snaps and bursts are not acceptable.

(ii) There were few responses where the student had calculated from the graph that the RCCB had to switch off within 60 milliseconds. Many students seemed to have missed the instruction to use information from the diagram or did not understand the significance of the difference in the current in the live and neutral wires. A number of students did gain a mark for the idea that the RCCB was fast, quick or acted immediately. Some students thought that ‘automatically’ was the same as fast. A few students misunderstood the graph and thought incorrectly that the RCCB switched the circuit off faster if the current was higher.

E16. (a) (i) Nearly all students scored both marks. Those students that did not often divided by 10 rather than multiplying.

(ii) Only just over a third of students realised that at constant speed the resultant force is zero and so the force T must equal the weight of the person. The most common errors were dividing 720 by 10 to get 72, or simply adding 1 to 720 to give 721.

(b) (i) Most students scored this mark.

(ii) Nearly half of students scored all three marks with a further third scoring two marks for the calculation. It seems surprising that a significant number of students failed to choose a unit at all thereby potentially wasting one mark.

E17. (a) (i) Just over three fifths of students recognised the incomplete circuit. However there was a little confusion over how to express the idea. The switches were often described as not being connected, clearly they are connected but not in a position to form a closed circuit.

(ii) The vast majority of students showed a correct substitution of the two numbers with a subsequent correct calculation.

(iii) Just over three fifths of students scored this mark. Those students that did not usually thought that the total resistance would go down and so divided by two.

(b) Just under half of the students were able to express a clear advantage of using two switches. Weaker students expressed ideas such as ‘it’s safer’ or ‘it wastes less energy’ without giving any further detail. Some students read the question as having two bulbs rather than two switches and gave responses such as ‘if one bulb breaks the other will still work’.

(c) (i) This was well answered by nearly all students. Favourite answers were receiving an electric shock or electrocution. A few students interpreted the question as ‘why’ rather than ‘what’ and wrote ‘the earth wire was unconnected’.

(ii) Just over three fifths of students knew that the earth wire needed connecting. Some students wanted to cover the wires with plastic, whilst others wanted to connect the earth wire to a fuse.

E18. (a) (i) Just over half of the candidates could identify the correctly wired plug.

(ii) Almost all candidates gave plastic or rubber as a suitable material for the casing of a plug.

(b) This part question was answered well. However it was not uncommon to have a correct substitution shown (2 × 230) with an answer of 660.

(c) Unfortunately, few candidates were able to explain correctly the advantage to the householder of buying a plug without a fuse fitted. There were many incorrect responses in terms of the smaller ampage fuses restricting the flow of electricity to an appliance in order to save energy (and money). Rather worryingly, there were far too many candidates who thought that the smaller amp fuses were less likely to blow than a 13 amp fuse, and consequently, the 13 amp fuse was in some way safer. A significant number of candidates seem to think that the fuse provides the current.

E19. (a) (i) Less than a quarter of candidates applied the rule for current in a series circuit to arrive at the answer 0.25 A. The vast majority of candidates multiplied the series current by the number of lamps to arrive at an incorrect answer of 5 A.

(ii) Just under two-thirds of candidates used the equation correctly to gain both calculation marks. About three-tenths of candidates lost one mark because they failed to convert the time from minutes into seconds. Only just over a third of candidates knew that the unit of charge is the coulomb. A substantial number failed

to give any unit or offered one of a range of other electrical units.

(b) Many candidates showed a good understanding of why a piece of aluminium foil is not an appropriate replacement for a fuse, and they could use good scientific language to explain their ideas and gain full marks. Some candidates got sidetracked too far into describing how a fuse functions in a faulty circuit without then going on to say why the aluminium foil presents a danger. Many of the poorer answers were long and rambling, with wrong physics such as ‘too much voltage goes through the foil’, and ‘explosions’ in many of the responses scoring zero. In contrast, some of the best responses covered all four of the possible mark points in a succinct sentence or two.

E20. (a) Surprisingly, only just over two fifths of candidates were able to give the correct colour.

(b) Only a quarter of candidates achieved credit for stating that the plastic obviated the need for an earth wire to be fitted to the hairdryer. Of the incorrect responses, many implied that the whole of the hairdryer was constructed of plastic materials or that the current needed by the hairdryer was so low that an earth wire was not required.

(c) (i) Most candidates were able to identify switch S1 as operating the fan, but only about two fifths of candidates were able to identify the switches needed to operate heater 2.A common error was only giving S3 for the operation of heater 2. Many candidates’ handwriting was such that examiners struggled to distinguish between a suffix 1 and a suffix 2.

(ii) The majority of candidates scored no marks in this part question. Candidates seemed to be confused about whether the fan part and/or heater parts of the circuit were in series or parallel and how this would affect the different branches of the circuit. Many candidates referred to a ‘fan switch’without making it clear which of the three switches was intended.

(d) Unfortunately many candidates ignored the request to give the appropriate unit and were thus denied full credit for this part question. Incorrect numerical responses were mostly from the candidates using the wrong current, usually by adding the three currents together from the table supplied. It is not encouraging that the presence of more than two numbers caused such confusion.

E21. (a) (i) Only about a fifth of candidates scored full marks, with a further two fifths of candidates scoring one mark, usually losing the mark for the misplacing of the voltmeter. Scripts with higher marks usually had candidates drawing the circuits with

the use of a ruler. Perhaps using a ruler indicated they would be careful when drawing the components. The most common error was joining both the ammeter and voltmeter in series suggesting a lack of practical experience. Others placed the voltmeter across the wrong component or even across a lead, and some lost marks for careless diagrams, notably lines drawn through meters and gaps in the circuit.

(ii) Just over half the candidates scored this mark. Many candidates believe that it is thevalue of d.c. which does not change, and many responses appeared based on the appearance of a.c. and d.c. on an oscilloscope. Another common incorrect response referred to d.c. going straight to the component.

(b) (i) Approximately three quarters of candidates completed the calculation correctly. Weaker candidates struggled to transform the equation.

(ii) The relationship between current and resistance is, generally, well understood and four fifths of candidates scored this mark. Weaker candidates often used inappropriate language; the use of ‘stronger’ resistance was one such example. Candidates would benefit by using the stem to help their wording; if the word decrease is used in the stem it makes sense to respond with the word increase and not seek synonyms which are less appropriate.

(iii) Many candidates realised that elastic energy is stored but under half of candidates gained the mark since many failed to include the word potential in their answer. The wrong answers often referred to kinetic energy.

E22. (a) (i) It was comforting to know most candidates were aware of the potential hazards shown in the incorrectly fitted three-pin plug. However, credit was not given for simply identifying the two faults as the question specifically asked for what remedial action was needed to make the plug safe.

(ii) Most candidates were able to identify the correct wire, either by name or colour code, the most common incorrect response was to give the live wire.

(iii) Most candidates were able to achieve one mark in this part question. However candidates often tended to exaggerate the effect of an excess current. Many candidates referred to ‘explosions’, ‘blowing up’, ‘spectacular sparking’ and the fuse going ‘pop’. For those who didn.t use the word melt the idea of a fuse blowing was accepted. Some candidates seem to think that a fuse, in itself, causes sparking to occur.

(b) There were many long winded responses produced with few blank answers. The most common error was to identify the danger as being due to the hairdryer being plugged into a socket or the wall rather than to state that the hairdryer operated at mains voltage.Candidates could not explain that mains voltage would cause a potentially fatal current while the radio’s low voltage would not. A common response was that the hairdryer contained a fuse and would cause sparking if it fell in the water, while the radio had no fuse and was therefore safe. A worrying number stated that the radio did not use electricity.

E23. (a) Less than one fifth of candidates were able to complete both the calculation and give the correct unit. Many candidates did not calculate the time period correctly or gave the time period as their final answer.Those who scored one mark usually scored this from part of the calculation, as the unit was not well known. Nearly a third of candidates scored zero.

(b) Less than half of the candidates were able to recall this, the most frequent incorrect response being 230 (V).

E24. (a) Many candidates were able to give a brief, correct response that current is the movement of electrons or charges. A smaller number of candidates gave the answer that current is the rate of flow of charge. The most common reason for failing to score the mark was to be imprecise or incorrect about what it is that flows, for example ‘the flow of electricity’, or .‘the flow of energy’.

(b) Only just over a quarter of candidates were able to present a clear calculation arriving at the correct numerical answer with the correct units. Many other candidates gained some credit for showing correct calculation steps, such as transposing the equation and substituting correct data. Common reasons for loss of a mark were misreading the power value from the graph, putting values into an incorrect re-arrangement of the equation, usually 230/1.6 or 1600 or failing to convert 1.6 kW to 1600 W. A surprising number of candidates gave the wrong unit or omitted it. Incorrect units seen included coulombs, ohms or a combination of units such as kW/V.