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
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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.
(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.
(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
GCSE Physics Revision: 2) Electricity V1
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)
GCSE Physics Revision: 2) Electricity V1
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)
GCSE Physics Revision: 2) Electricity V1
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:
GCSE Physics Revision: 2) Electricity V1
• 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
GCSE Physics Revision: 2) Electricity 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
GCSE Physics Revision: 2) Electricity V1
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]
GCSE Physics Revision: 2) Electricity V1
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
GCSE Physics Revision: 2) Electricity V1
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.