Currents in electrical circuits
P2
73 minutes
73 marks
Page 1 of 31
Q1.
(a)
(i)
The diagram shows the inside of a three-pin plug.
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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(1)
Page 2 of 31
(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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(2)
(ii)
Earthing an appliance helps to protect a person against a possible risk.
What is the risk?
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(1)
(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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(1)
Page 3 of 31
(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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(2)
(Total 10 marks)
Q2.
(a)
Electrical circuits often contain resistors.
The diagram shows two resistors joined in series.
Calculate the total resistance of the two resistors.
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Total resistance = .................................................. Ω
(1)
Page 4 of 31
(b)
A circuit was set up as shown in the diagram. The three resistors are identical.
(i)
Calculate the reading on the voltmeter.
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Reading on voltmeter = .................................................. V
(2)
(ii)
The same circuit has now been set up with two ammeters.
Draw a ring around the correct answer in the box to complete the sentence.
smaller than
The reading on ammeter A2 will be
equal to
the reading on ammeter A1.
greater than
(1)
(Total 4 marks)
Page 5 of 31
Q3.
(a) The diagram shows a negatively charged plastic rod held near to a thin stream of
water. The water is attracted towards the rod.
Which one of the following statements explains what is happening to the charge in the
water?
Tick (
) one box.
The positive and the negative charges in the water are attracted
to the rod.
The positive and the negative charges in the water are repelled
by the rod.
The negative charge in the water is repelled by the rod and the
positive charge is attracted to the rod.
The negative charge in the water is attracted to the rod and the
positive charge is repelled by the rod.
(1)
Page 6 of 31
(b)
A company that produces bottles of mouthwash found a problem with the automatic filling
system.
As the bottles go towards the filler, the bottles move around on the conveyor belt and
become electrostatically charged. This causes the stream of mouthwash to move
sideways, missing the open top of the bottle.
The company came up with an answer to the problem. Before the bottles reach the dfiller,
the bottles pass through a stream of ionised air. The ions in the air neutralise the charge
on the bottles.
(i)
Explain why the plastic bottles became charged.
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(2)
(ii)
What happens to the structure of an atom to change the atom into an ion?
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(1)
(iii)
Earthing the conveyor belt with a conducting wire would not have solved this
problem.
Give a reason why.
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(1)
(Total 5 marks)
Page 7 of 31
Q4.
(a) The diagram shows the circuit used to investigate the resistance of a sample of a
material.
The diagram is not complete; the ammeter and voltmeter are missing.
(i)
Draw the symbols for the ammeter and voltmeter on the diagram in the correct
places.
(2)
(ii)
How can the current through the material be changed?
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(1)
Page 8 of 31
(b)
The material, called conducting putty, is rolled into cylinders of different lengths but with
equal thickness.
Graph 1 shows how the resistance changes with length.
Length in centimetres
(i)
The current through a 25 cm length of conducting putty was 0.15 A.
Use Graph 1 to find the resistance of a 25 cm length of conducting putty.
Resistance = .................................................. ohms
(1)
(ii)
Use your answer to (b) (i) and the equation in the box to calculate the potential
difference across a 25 cm length of conducting putty.
potential difference = current x resistance
Show clearly how you work out your answer.
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Potential difference = .................................................. volts
(2)
Page 9 of 31
(c)
A second set of data was obtained using thicker pieces of conducting putty. Both sets of
results are shown in Graph 2.
Length in centimetres
(i)
What is the relationship between the resistance and the thickness of the conducting
putty?
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(1)
(ii)
Name one error that may have reduced the accuracy of the results.
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(1)
(iii)
How could the reliability of the data have been improved?
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(1)
(Total 9 marks)
Page 10 of 31
Q5.
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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(1)
(ii)
What happens, as the cable is cut, to cause the RCCB to switch the circuit off?
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(2)
(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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(1)
(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)
Page 11 of 31
(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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(2)
(Total 11 marks)
Q6.
(a) The resistance of a 24 W, 12 V filament lamp depends on the current flowing through
the lamp. For currents up to 0.8 A, the resistance has a constant value of 2.5 Ω.
(i)
Use the equation in the box to calculate the potential difference across the lamp
when a current of 0.8 A flows through the lamp.
potential difference
=
current
×
resistance
Show clearly how you work out your answer.
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Potential difference = ............................................................ V
(2)
Page 12 of 31
(ii)
When the potential difference across the lamp is 12 V, the current through the lamp is 2 A.
On the axes below, draw a current–potential difference graph for the filament lamp over the
range of potential difference from 0 to 12 volts.
(2)
(iii)
Why does the resistance of the lamp change when the current through the lamp
exceeds 0.8 A?
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(1)
Page 13 of 31
(b)
The lamp is now included in a circuit. The circuit is switched on for 2 minutes. During this
time, 72 coulombs of charge pass through the lamp.
Use the equation in the box to calculate the energy transformed by the lamp while the
circuit is switched on.
energy transformed
=
potential difference
×
charge
Show clearly how you work out your answer.
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Energy transformed = ............................................................ J
(2)
(Total 7 marks)
Q7.
A student has designed the circuit shown in the diagram to measure the water level in a
beaker. The student is going to use the ammeter to indicate the water level.
(a)
Use words from the box to label the three components, J, K and L, on the diagram.
battery
cell
fuse
lamp
resistor
switch
(3)
Page 14 of 31
(b)
The resistance of the variable resistor changes as the cork moves up and down inside the
beaker. This changes the electric current flowing in the circuit.
(i)
What is meant by the term electric current?
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(1)
(ii)
When a voltmeter was mistakenly added to the circuit in series, the reading on the
ammeter was zero.
Suggest why.
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(1)
(c)
The table gives the variable resistor value and the ammeter readings for different water
levels. The table is not complete.
Variable resistor
value in ohms
Ammeter reading
in amps
Full
0
2.0
Half full
9
0.8
Empty
18
Water level
Calculate the reading on the ammeter, in amps, when the beaker is empty.
Assume the ammeter, battery, fuse and wires have zero resistance.
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Ammeter reading = .............................................. A
(3)
Page 15 of 31
(d)
A second student copied the design using a 2A fuse, but he forgot to include the 6Ω resistor.
What will happen to the fuse in this circuit as the water reaches the top of the beaker?
Explain your answer.
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(5)
(Total 13 marks)
Q8.
Electrical circuits have resistance.
(a)
Draw a ring around the correct answer to complete the sentence.
decreases.
When the resistance of a circuit increases, the current in the circuit increases.
stays the same.
(1)
(b)
Use the correct answer from the box to complete each sentence.
a filament bulb
an LED
an LDR
An electrical component which has a resistance that increases as the
temperature increases is .................................................. .
An electrical component which emits light only when a current flows through it
in the forward direction is .................................................. .
(2)
Page 16 of 31
(c)
When some metals are heated the resistance of the metal changes.
The equipment for investigating how the resistance of a metal changes when it is heated is
shown in the diagram.
In this question you will be assessed on using good English, organising information clearly
and using specialist terms where appropriate.
Describe an investigation a student could do to find how the resistance of a metal sample
varies with temperature. The student uses the equipment shown.
Include in your answer:
•
how the student should use the equipment
•
the measurements the student should make
•
how the student should use these measurements to determine the resistance
•
how to make sure the results are valid.
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Page 17 of 31
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(6)
(d)
The table shows some data for samples of four metals P, Q, R and S.
The metal samples all had the same cross-sectional area and were the same length.
Metal sample
Resistance at 0°C
in ohms
Resistance at 100°C
in ohms
P
4.05
5.67
Q
2.65
3.48
R
6.0
9.17
S
1.70
2.23
A graph of the results for one of the metal samples is shown.
Temperature in °C
Page 18 of 31
(i)
Which metal sample, P, Q, R or S, has the data shown in the graph?
(1)
(ii)
One of the results is anomalous. Circle this result on the graph.
(1)
(iii)
Suggest a reason for the anomalous result.
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(1)
(iv)
The same equipment used in the investigation could be used as a thermometer
known as a ‘resistance thermometer.’
Suggest two disadvantages of using this equipment as a thermometer compared to
a liquid-in-glass thermometer.
1 .............................................................................................................
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2 .............................................................................................................
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(2)
(Total 14 marks)
Page 19 of 31
M1.
(a)
(i)
neutral
1
(ii)
brown
1
(b)
(i)
centre symbol ringed
accept any correct indication
1
(ii)
fuse (wire) melts
accept fuse blows
accept fuse breaks / snaps
accept burns out appliance doesn’t work is insufficient
overheat is insufficient
do not accept blows up
1
(c)
(i)
Toaster
1
(only one with) a metal case / outside
reason only scores if toaster chosen
accept it is metal
accept outside / case / metal conducts (electricity)
do not accept it conducts electricity
1
(ii)
electric shock / electrocution
do not accept explosion
1
(d)
overheating of cables or fire
it refers to the electric cable
accept short circuit / sparking
overheating of tape is insufficient
do not accept electrocution / shock
1
(e)
stop cable(s) being pulled loose / free
accept 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 work
1
[10]
Page 20 of 31
M2.
(a)
25(Ω)
1
(b)
(i)
2(V)
allow 1 mark for showing a correct method, ie 6 / 3
2
(ii)
equal to
1
[4]
(a) 3rd box
The negative charge in the water is repelled by the rod and the positive charge
is attracted to the rod.
M3.
1
(b)
(i)
friction between bottles and conveyor belt / (plastic) guides
accept bottles rub against conveyor belt / (plastic) guides
1
charge transfers between bottles and conveyor belt / (plastic) guides
accept specific reference eg electrons move onto / off the bottles
reference to positive electrons / protons negates this mark
1
(ii)
(the atom) loses or gains one (or more) electrons
1
(iii)
charge will not (easily) flow off the conveyor belt / bottles
accept the conveyor belt / bottles is an insulator / not a conductor
accept conveyor belt is rubber
1
[5]
M4.
(a)
(i)
ammeter symbol correct and drawn in series
accept
do not accept lower case a
1
voltmeter symbol correct and drawn in parallel with the material
do not accept
1
Page 21 of 31
(ii)
adjust / use the variable resistor
accept change the resistance
or
change the number of cells
accept battery for cell
accept change the pd / accept change the voltage
accept increase / decrease for change
1
(b)
(i)
37.5 (Ω)
accept answer between 36 and 39 inclusive
1
(ii)
5.6(25) or their (b)(i) × 0.15
allow 1 mark for correct substitution ie 37.5 or their (b)(i) × 0.15
provided no subsequent step shown
2
(c)
(i)
the thicker the putty the lower the resistance
answer must be comparative
accept the converse
1
(ii)
any one from:
•
measuring length incorrectly
accept may be different length
•
measuring current incorrectly
do not accept different currents
•
measuring voltage incorrectly
do not accept different voltage
•
ammeter / voltmeter incorrectly calibrated
•
thickness of putty not uniform
do not accept pieces of putty not the same unless qualified
•
meter has a zero error
do not accept systematic / random error
accept any sensible source of error eg putty at different
temperatures
do not accept human error without an explanation
do not accept amount of putty not same
1
(iii)
repeat readings and take a mean
accept check results again
accept do experiment again
accept do it again and take mean(s)
accept compare own results with other groups
do not accept take more readings
1
[9]
Page 22 of 31
M5.
(a)
(i)
50(Hz)
ignore any unit given
1
(ii)
any two from:
•
(some) current flows to Earth
accept ground for Earth
•
current flows through copper braid
accept current flows through the earth wire
accept electricity for current in either the first or second marking
point but not both
•
RCCB detects difference between current in live and neutral wire
2
(iii)
can be reset
accept does not need replacing
or
faster acting
accept 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 / C
do not accept c
1
(ii)
18 216 000
accept for 2 marks 18 216 kJ or 18.216 MJ
or
230 × their (b)(i) correctly calculated
allow 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 thermistor
1
changes resistance (of thermistor)
do not accept increases resistance (of thermistor)
an answer decreases resistance (of thermistor) gains 2 marks
1
[11]
Page 23 of 31
M6.
(a)
(i)
2
allow 1 mark for correct substitution i.e. 0.8 × 2.5 provided no
further step shown
2
(ii)
straight line drawn from origin to 2, 0.8
or
their (a)(i), 0.8
1
curve from 2, 0.8 to 12,2
or
their (a)(i) 0.8 to 12,2
accept curve from 2, 0.9 to 12,2
or
their (a)(i) 0.9 to 12,2
‘convex’ curve required
accept a curve that flattens between 10 and 12V
1
(iii)
filament / lamp gets hot
accept temperature increases
1
(b)
108
allow 1 mark for correct substitution i.e. 1.5 × 72 provided no
further step shown
2
[7]
M7.
(a)
J fuse
1
K switch
1
L battery
1
(b)
(i)
a flow of (electrical) charge
1
(ii)
because voltmeters have a very high resistance
1
(c)
total resistance = 24 Ω
1
1
Page 24 of 31
0.5 (A)
correct answer with or without working gains 3 marks
an answer of 0.66▪ or 0.67 gains 2 marks
alone gains 1 mark
1
(d)
the fuse melts
1
therefore breaking the circuit
1
because without the 6 Ω resistor as the water reaches the top of
the beaker the total resistance approaches 0 Ω
1
therefore the current rises above the 2 A fuse rating
1
and the heating effect increases
1
[13]
M8.
(a)
decreases
1
(b)
a filament bulb
allow bulb
1
an LED
1
Page 25 of 31
(c)
Marks awarded for this answer will be determined by the Quality of Communication
(QoC) as well as the standard of the scientific response.
0 marks
No relevant content.
Level 1 (1−2 marks)
There is a basic description of the method. This is incomplete and would not lead to
any useful results.
Level 2 (3−4 marks)
There is a description of the method which is almost complete with a few minor
omissions and would lead to some results.
Level 3 (5−6 marks)
There is a detailed description of the method which would lead to valid results.
To gain full marks an answer including graph, or another appropriate representation
of results, must be given.
examples of the physics points made in the response:
•
•
•
•
•
•
read V and I
read temperature
apply heat
allow hot water to cool
read V and I at least one other temperature
determine R from V / I
range of temperatures above 50 °C
extra detail:
•
use thermometer to read temperature at regular intervals of temperature
•
remove source of heat and stir before taking readings
•
details of attaining 0 °C or 100 °C
•
last reading taken while boiling
•
graph of R against T
•
at least 3 different temperatures
6
(d)
(i)
Q
1
(ii)
(80, 3.18)
1
(iii)
any one from:
•
•
•
•
measurement of V too small
measurement of I too big
incorrect calculation of R
thermometer misread
allow misread meter
ignore any references to an error that is systematic
1
Page 26 of 31
(iv)
any two from:
•
•
•
not portable
allow requires a lot of equipment allow takes time to set up
needs an electrical supply
cannot be read directly
accept it is more difficult to read compared to liquid-in-glass
2
[14]
Page 27 of 31
E1.
(a)
(b)
(c)
(i)
Half of the students scored this mark.
(ii)
This was better known with a majority of students giving the correct answer.
(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.
(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.
E2.
(a) A large proportion of the students provided the correct answer of 25 ohms. The most
common incorrect response was 5 ohms, achieved by subtracting the numerical values of
the resistors.
(b)
E3.
(i)
Almost half of students gained both marks, with very few gaining one mark. Common
incorrect answers were achieved by multiplying or dividing the answer to part (a) by
6.
(ii)
Perhaps surprisingly, only just over half of the students knew that the two ammeters
would have the same reading.
(a)
(b)
About half of the students gained this mark.
(i)
About half of the students gained one mark for the idea that the bottles rubbed
against the conveyor belt / guides. Few students went on to link this to the transfer of
charge.
(ii)
About half of the students were able to state what happens to change an atom into
an ion.
(iii)
Very few students gained this mark even though a simple answer like ‘the conveyor
belt is rubber’ was sufficient.
Page 28 of 31
E4.
(a)
(b)
(c)
E5.
(c)
This was poorly answered. Just over half of the students could put the ammeter
into the circuit correctly but few could add the voltmeter correctly. Common errors
included using the wrong symbol and / or placing the voltmeter in series.
(ii)
Just under half of the students gained this mark, usually for adding or subtracting a
cell or simply stating ‘change the volts’.
(i)
About two thirds of students were able to extrapolate the graph line to obtain the
correct value.
(ii)
Those students scoring a mark in part (b)(i) were usually able to go on to score both
marks in this part.
(i)
About three quarters of students were able to give an acceptable version of the
relationship. A significant number of students answered in terms of length rather than
thickness as instructed.
(ii)
Many students considered the error to be one of plotting, very few gave an
acceptable answer.
(iii)
A majority of students gained the mark for this part.
(a)
(b)
(i)
(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.
(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.
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.
Page 29 of 31
E6.
(a)
(b)
E8.
(i)
The majority of students, over 90%, scored 2 marks. Very few gained 1 mark.
(ii)
Very few students produced a correct graph to gain 2 marks. A large percentage of
students did not appreciate the importance of using the answer to part (a)(i).
Common “wrong” answers included a straight line from the origin to (12,2), a straight
line from (12,2) through (2,0.8) and continued back to the y axis, and two straight
lines, one from origin to (2,0.8) and then from that point to (12,2). Otherwise, all sorts
of curves, including s-shaped and convex all the way from the origin.
(iii)
There were only a minority of correct answers, less that 25%. Many answers
referred to how the resistance changed as the current increased but not why. There
were also lots of answers given in terms of the resistance changing to allow or stop
the current flowing and for safety to keep the “fuse” from blowing.
The majority of students gave correct answers. The most common incorrect response
was “144”, by multiplying the charge by the time in minutes. An answer scoring one mark
was rare – and seemingly from students who did not possess a calculator.
(a) Nearly all students knew that when the resistance of a circuit increases the current in it
decreases.
(b)
Nearly three-quarters of the students recognised the description of a filament bulb and a
LED.
(c)
The Quality of Communication question was a description of an experiment where the
change in resistance of metal with temperature was investigated.
Many students wasted time, and used a substantial fraction of the answer lines, describing
the electrical circuit provided. Just under half of the students scored four marks out of six
for an adequate account that could be repeated to give sufficient data.
Students who scored more than four marks often included a graph of resistance against
temperature or some detail such as removing the Bunsen burner and stirring the water
before taking readings.
Those who scored three marks or less often did not state how resistance could be
calculated from the meter readings, or did not state that the meters had to be read at all
but that ‘resistance had to be recorded’ at each temperature.
(d)
(i)
Almost all students could relate a range of resistance values in a table to those
represented on a graph.
(ii)
Almost all students were able to circle an anomalous value on the graph.
(iii)
Surprisingly, less than half the students were able to suggest a reason for the
anomalous results such as misreading the thermometer or meters or incorrectly
calculating resistance.
(iv)
About a third of students were able to suggest a disadvantage of a resistance
thermometer compared to a liquid-in-glass thermometer. About one tenth could
suggest two, including the need for an electrical supply and that temperature could
not be read directly.
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