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GCSE Physics Revision: 2) Electricity V1

Q1.We use mains electricity in our homes.

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

Tick one box.

23 Hz

50 Hz

230 Hz

500 Hz

(1)

(b) Many appliances in the home use three-core electrical cable.

Look at the figure below.

Label the wires in the cable in the figure above.

Use words from the box.

Earth Negative Neutral Positive

(2)

(c) The sentences explain how touching the live wire in a cable can cause an electric shock.

Complete the sentences.

Use words from the box.

current force resistance potential difference

Touching the live wire causes a large _____________________ to exist across the body.

This causes a _________________ through the body, which results in an electric shock.

(2)


(d) A heater has a power rating of 2500 W.

The heater is turned on for 180 seconds.

Calculate the energy transferred by the heater.

Use the equation:

energy transferred = power × time

Give your answer in kilojoules (kJ).

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Energy transferred = _________________ kJ(3)

(e) Write down the equation that links charge flow, energy transferred and potential difference.

___________________________________________________________________(1)

(f) The mains electricity supply is at 230 V.

A different heater transfers 4200 J of energy.

Calculate the charge flow through the heater.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Charge flow = _________________ C(3)

(Total 12 marks)Q2.

(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?

______________________________________________________________(1)


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

______________________________________________________________(1)

(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.

Choose the unit from the list below.

amps volts watts

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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?

___________________________________________________________________

___________________________________________________________________(2)

(Total 7 marks)

Q3.(a) The diagram shows a simple circuit.

(i) Calculate the total resistance of the two resistors in the circuit.

______________________________________________________________

Total resistance = _________________________ Ω(1)

(ii) Calculate the reading on the voltmeter.

Show clearly how you work out your answer.

______________________________________________________________

______________________________________________________________

Voltmeter reading = _________________________ V(2)

(iii) Draw a ring around the correct answer in the box to complete the sentence.

Replacing one of the resistors with a resistor of higher value will

decrease

not change

increase

the reading on the ammeter.(1)


(b) The voltmeter in the circuit is replaced with an oscilloscope.

Which one of the diagrams, X, Y or Z, shows the trace that would be seen on the oscilloscope?

Write your answer, X, Y or Z, in the box.

Diagram

Give a reason for your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(Total 6 marks)

Q4.An electric current is a flow of electrical charge through a circuit.

(a) Complete the sentence.

Use a word from the box.

atoms electrons ions molecules

Metals are good conductors of electricity because electrical charge is transferred

by delocalised __________________________(1)


(b) Draw one line from each symbol to the name of the component.

Standard symbol Name of component

(3)

(c) The table below shows information about some electrical appliances.

Electrical appliance Power in watts

Hairdryer

1500

Kettle

2500

Electric hob

3000

Television

360

A student plugs all four of the appliances into one multi-way socket.

The mains electricity is 230 V.


The highest safe current in the socket is 30 A.

Explain why it is not safe to use all four appliances at the same time.

In your answer you should:

• calculate the total power needed

• use the equation

current = power ÷ potential difference

to calculate the total current needed.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(4)

(d) The figure below shows how electrical power is transferred from power stations to consumers using the National Grid.

Transformer 1 is a step-up transformer.

Explain why step-up transformers are used in the National Grid.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________


___________________________________________________________________(3)

(e) What is the purpose of Transformer 2?

___________________________________________________________________

___________________________________________________________________(1)

(f) In a power station 900 MJ of thermal energy were released by burning natural gas.

Write down the equation that links efficiency, useful input energy transfer and useful output energy transfer.

___________________________________________________________________(1)

(g) In a power station 900 MJ of thermal energy were released by burning natural gas.

Only 405 MJ was generated.

Calculate the efficiency of this energy transfer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Efficiency = _________________(2)

(Total 15 marks)

Q5.A student used electrical circuits to investigate the relationship between resistance, potential difference and current.

Figure 1 shows how the student connects the first circuit he set up.

Figure 1

(a) The circuit does not work.

Draw the correct circuit.


(2)


(b) The student then sets up the circuit correctly.

Look at Figure 2.

Figure 2

What is the reading on the voltmeter?

___________________________________________________________________(1)

(c) The student then set up a circuit to investigate how resistance affects the brightness of a lamp.

Figure 3 shows the circuit he set up.

Figure 3

The student increases the resistance of the variable resistor.

What effect does this have on the brightness of the lamp?

Explain your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(d) Write down the equation that links current, potential difference and resistance.

___________________________________________________________________


(1)

(e) When the potential difference across the lamp is 3.3 V the current is 0.15 A.

Calculate the resistance of the lamp in the student’s experiment.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Resistance = _________________ Ω(3)

(Total 9 marks)

Q6.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?

______________________________________________________________(1)

(ii) Calculate the charge passing through one of the lamps in 5 minutes.

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

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

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.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(Total 6 marks)

Q7.A student is investigating some electrical components.

(a) Describe how the student could set up a circuit to find the resistance of a lamp.

You should include a circuit diagram in your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(4)

(b) The student is given an electrical component in a sealed box.

She has to find out what the electrical component is by experiment.

The student records the current and the potential difference for the component.

Her results are shown in the figure below.


Explain how the student could know that the electrical component in the sealed box is not an ohmic conductor.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(2)

(c) What is the electrical component in the sealed box?

Explain your answer.

Component _______________________________________________________

Explanation _______________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(3)


(d) Use the graph to determine the resistance of the component at 2.3 V.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Resistance = __________________ Ω(4)

(Total 13 marks)

Q8.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

___________________________________________________________________

___________________________________________________________________


potential difference

___________________________________________________________________

___________________________________________________________________(2)

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

Explain why.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________(3)

(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.

Show clearly how you work out your answer.

___________________________________________________________________

___________________________________________________________________

Rate of energy transfer = __________________ W(2)

(Total 7 marks)


Mark schemes

Q1.(a) 50 Hz

1

(b) Top: Earth1

Bottom: Neutral1

(c) potential difference1

current1

(d) energy = 2500 × 1801

= 450 0001

= 450 kJ1

allow 450 with no working shown for 3 marks

(e) energy transferred = charge flow × potential differenceallow E = QV

1

(f) 4 200 = Q × 2301

Q = 4 200 ÷ 2301

= 18.3 (C)1

allow 18.3 with no working shown for 3 marks[12]

Q2.(a) (i) 50 (Hz)

1

(ii) 2760 (W)1

(b) 12allow 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]

Q3.(a) (i) 15

1

(ii) 4.5 or their (a)(i) x 0.3 correctly calculatedallow 1 mark for correct substitution, ie 0.3 x 15/their (a)(i), provided no subsequent step

2

(ii) decrease1

(b) Yaccept any correct indicationreason only scores if Y is chosenaccept voltage for p.d.

1

(only one that) shows a direct current / p.d.ora battery / cell gives a direct current

accept both X and Z are a.c.

ora battery/cell gives a constant current/p.d.

accept it’s a constant current/p.d.it is not changing is insufficient

1[6]

Q4.(a) electrons

1

(b)


extra lines from a symbol negate the mark

3

(c) the total power = 7360 watts1

current = 7360 ÷ 2301

= 32 Aallow 32 with no working shown for 3 marks

1

so the current is greater than 30 A1

(d) to increase the voltage (across the cables) or to decrease the current (through the cables)

1

reducing energy losses (in the cables)do not allow electricity for energydo not allow no energy loss

1

increasing the efficiency of transmission1

(e) to decrease the potential difference for domestic use1

(f) 1

(g) 405 / 9001

=0.45accept 45%

1

allow 0.45 or 45% with no working shown for 2 marks[15]

Q5.(a)


battery connected correct way round

1

ammeter and voltmeter correct way round1

(b) 6.4 V1

(c) (the lamp will) get dimmer1

because increasing the resistance decreases the current1

(d) potential difference = current × resistanceallow V = IR

1

(e) 3.3 = 0.15 × R1

R = 3.3 ÷ 0.151

= 22(Ω)1

allow 22 with no working shown for 3 marks[9]

Q6.(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]

Q7.(a)

ammeter connected in series

1

voltmeter connected in parallel1

measure the potential difference across the lamp at known current1

calculate resistance from measured values using V = IR1

(b) for ohmic conductors the current is directly proportional to the potential difference applied across it

1

this graph is curved so it is not an ohmic conductor1

(c) diode1

because it has a high resistance with negative potential differences1

and a low resistance for positive potential differences.1

allow answers in terms of current

(d) tangent to the curve drawn at 2.3 V1


correct reading of Δy and Δx from graph1

either

substitution of values into V = IR (1)1

value of R calculated (1)accept values in the range 0.50 to 0.65

1

or

calculation of gradient (1)allow ecf from incorrect readings of Δy and Δx

calculation of R = 1 / gradient (1)accept values in the range 0.50 to 0.65

[13]

Q8.(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 collide


accept 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]


Examiner reports

Q2.(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.

Q3.

(a) (i) About two-thirds of students correctly added the resistances together to give an answer of 15.

(ii) Just under half the students were able to use the answer to part (a)(i) to correctly calculate the reading on the voltmeter. The most common error seen was dividing by the current rather than multiplying by it.

(iii) Only a third of students scored this mark. Most students thought that using a higher value resistor would cause an increase in the current.

(b) Only a small minority of students identified Y as being the oscilloscope trace for a d.c. current, with even fewer students stating a correct reason for their choice.

Q6.

(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.

Q8.

(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.

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