P2 Revision Booklet

Circuits

Medium (Grade C)

Q1.The diagram shows the circuit set up by a student.

(a)     The student uses the circuit to test the following hypothesis:
‘The current through a resistor is directly proportional to the potential difference across the resistor.’
(i)      If the hypothesis is correct, what should the student predict will happen to the current through the resistor when the potential difference across the resistor is doubled?
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(1)

(ii)     Name the component in the circuit used to change the potential difference across the resistor.
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(1)

(b)     The student used the data obtained to plot the points for a graph of current against potential difference.

(i)      Why has the student plotted the points for a line graph and not drawn a bar chart?
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(1)

(ii)     One of the points has been identified by the student as being anomalous.
What is the most likely cause for this anomalous point?
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(1)

(iii)    Draw a line of best fit for these points.
(1)

(iv)     Does the data the student obtained support the hypothesis?
Give a reason for your answer.
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(1)
(Total 6 marks)
 
Q2.          A student designed the circuit below to measure temperature using a thermistor.

To calibrate the thermistor to measure temperature, the student placed the thermistor in a beaker of water at 0 °C and took the voltmeter reading. The student then heated the water slowly with a Bunsen burner. The student recorded the reading on the voltmeter every 10 °C.

(a)     (i)      Before calibrating the thermistor the student completed a risk assessment.
Write down one possible hazard that the student should have written in the risk assessment and what the student should do to reduce the risk of the hazard causing an injury.
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(2)

(ii)     At 0 °C the reading on the ammeter is 0.5 A.
Calculate the reading on the voltmeter at 0 °C.
Write down the equation you use, and then show clearly how you work out your answer.
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Voltmeter reading = ..................................... V
(2)

(b)     Most of the readings taken by the student are displayed in the graph.

(i)      Explain why the reading on the voltmeter changes when the temperature of the water increases.
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(3)

(ii)     What is the temperature interval that can be measured with this circuit?
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(1)

(iii)     Once calibrated, between which temperatures would this circuit give the greatest resolution for temperature readings?
Tick () one box.
 
20 °C to 40 °C		
40 °C to 60 °C		
60 °C to 80 °C		

Give a reason for your answer.
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(2)

(c)     Thermistors have many practical uses, including being used as a thermometer to measure temperature.
Give one other practical use for a thermistor.
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(1)
(Total 11 marks)
Q3.          The diagram shows a simple type of car rear window heater. The six heating elements are exactly the same.

          Each heating element has a resistance of 5 Ω. The current passing through each element is 0.4 A.
(i)      Calculate the total resistance of the six heating elements.
          Show clearly how you work out your answer.
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Total resistance = .............................. ohms
(2)

(ii)      Why is the current passing through each element the same?
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(1)

(iii)     What is the total current passing through the whole circuit?
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(1)

(iv)     How is the 12 volt potential difference of the car battery shared between the six heating elements?
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(1)
(Total 5 marks)
 
Q4.          (a)     The circuit diagram drawn below includes a component labelled X.

(i)                  Use the equation in the box to calculate the potential difference across the 8 ohm resistor.
 
potential difference = current × resistance	

Show clearly how you work out your answer.
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Potential difference = ................................................. volts
(2)

(ii)     What is the potential difference across component X?
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(1)

(b)     The graph shows how the resistance of component X changes with temperature.

(i)      What is component X?
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(1)

(ii)     Over which range of temperatures does the resistance of component X change the most?
Put a tick () next to your choice.
0 °C to 20 °C          
20 °C to 40 °C        
40 °C to 60 °C        
60 °C to 80 °C        
80 °C to 100 °C      
(1)
(Total 5 marks)

 Q5.          The drawing shows the circuit used to investigate how the current through a 5 ohm (Ω) resistor changes as the potential difference (voltage) across the resistor changes.

(a)     Draw, in the space below, a circuit diagram of this circuit. Use the correct symbols for each part of the circuit.

 

 

 
 
(2)

(b)     (i)      Write down the equation that links current, potential difference and resistance.
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(1)

(ii)     Calculate the potential difference across the 5 ohm (Ω) resistor when the current through the resistor equals 0.4 A. Show clearly how you work out your final answer.
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potential difference = .............................................. volts
(2)

(iii)     Complete the graph to show how the current through the resistor changes as the potential difference across the resistor increases from 0 V to 3 V. Assume the resistor stays at a constant temperature.

(2)

(c)     The resistor is replaced by a 3 V filament lamp. The resistance of the lamp increases as the potential difference across it increases. Why?
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(1)
(Total 8 marks)
 Q6.          (a)     The diagram shows the voltage-current graphs for three different electrical components.

          Which one of the components A, B or C could be a 3 volt filament lamp? Explain the reason for your choice.
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(3)

(b)     Using the correct symbols draw a circuit diagram to show how a battery, ammeter and voltmeter can be used to find the resistance of the wire shown.

(3)

(c)     When correctly connected to a 9 volt battery the wire has a current of 0.30 amperes flowing through it.
(i)      Give the equation that links current, resistance and voltage.
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(1)

(ii)     Calculate the resistance of the wire. Show clearly how you work out your answer and give the unit.
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Resistance = .........................................................
(3)

(iii)     When the wire is heated, the current goes down to 0.26 amperes. State how the resistance of the wire has changed.
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(1)
(Total 11 marks)
 Q7.          The circuit diagram below shows a battery connected to a lamp and a switch.

(a)     State what happens to the lamp when:
(i)      the switch is open (OFF);
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(ii)     the switch is closed (ON).
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(2)

(b)     When the switch is closed what problem is caused in the circuit?
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(1)

(c)     In the space below draw a circuit diagram to show how the switch should be correctly connected to the lamp and battery.

 
(1)
(Total 4 marks)
Q8.          A student investigates how the current flowing through a filament lamp changes with the voltage across it.
She is given a filament lamp and connecting wires.
She decides to use a 15V power supply, a variable resistor, an ammeter, a voltmeter and a switch.

(a)     Complete the circuit diagram to show how she should set up the circuit.

 

 
(4)

(b)     The student obtains the following results.
VOLTAGE (V)	0.0 	3.0 	5.0 	7.0 	9.0 	11.0	
CURRENT (A)	0.0 	1.0 	1.4 	1.7 	1.9 	2.1	

(i)      Plot a graph of current against voltage.

(3)

(ii)     Use your graph to find the current when the voltage is 10V.
Current .................... A
(1)

(iii)     Use your answer to (ii) to calculate the resistance of the lamp when the voltage is 10V.
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Resistance .................... Ω
(2)

(c)     (i)      What happens to the resistance of the lamp as the current through it increases?
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(ii)     Explain your answer.
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(2)
(Total 12 marks)
 Q9.          In a hairdryer circuit there is a heater and a motor. It is important that the motor is always running when the heater is switched on.
(a)     Using the symbols shown below only once each, draw a circuit for a hairdryer.

 

 
(2)

(b)     Modern hairdryers are described as double insulated.
Explain what this term means.
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(2)

(c)     On a modern hairdryer handle it states:
1600 W               230 V                 50 Hz
(i)      [A]    Write an equation which shows the relationship between current, power and voltage.
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(1)

[B]     Calculate the current in the hairdryer when it is on full power.
Show clearly how you get your answer.
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Current = ........................... A
(2)

(ii)     [A]    Write an equation which shows the relationship between current, resistance and voltage.
          ................................................................................................................
(1)

[B]     The resistance of the heater is 20 ohms. Calculate the resistance of the motor.
          Show clearly how you get your answer.
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          ................................................................................................................
Resistance = ............... ohms
(2)
(Total 10 marks)
 Q10.          A computer is set up to produce a graph of the current through an electric lamp during the first few milliseconds after it is switched on.

          The lamp is modified then tested in the same way.

(a)     Describe three differences in the way the lamp behaves after it has been modified.
1.       ..........................................................................................................................
2.       ..........................................................................................................................
3.       ..........................................................................................................................
(3)

(b)     The current through the modified lamp depends on the total resistance of the filament and component X. 
          The smaller this total resistance is, the greater the current. 
          The following graphs show how the resistance of the lamp filament and component X change as the lamp heats up to its operating temperature.

          Use the information shown on the graphs to explain the behaviour of the modified lamp.
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(4)
(Total 7 marks)
 Circuits-Mark scheme

M1.         (a)      (i)     also double
increases is insufficient
1

(ii)     variable resistor
accept rheostat / potentiometer
1

(b)     (i)      the data / results / variables are continuous
accept data / results / variables are not categoric / discrete
1

(ii)     misreading the ammeter
do not accept misreading the meter / results
do not accept misreading the ammeter and / or voltmeter
reading / human error is insufficient
1

(iii)    straight line from the origin drawn passing close / through
points at 1 V, 5 V, 6 V and ignoring anomalous point
do not accept line drawn ‘dot-to-dot’
1

(iv)     yes
mark is for the reason
supports predictionor(straight) line passes through the origin
accept a mathematical argument, eg when p.d. went from 2 to 4 the current went from 0.3 to 0.6
it’s directly proportional is insufficient
1
[6]

M2.          (a)     (i)      spilling boiling / hot water
accept any sensible suggestion
1
suitable precaution to reduce risk from hot water eg
clamp the probe / complete the experiment standing
accept any sensible answer but must be linked to the named risk
1

(ii)     3 (V)
allow 1 mark for substitution into correct equation
ie 0.5 × 6
2

(b)     (i)      resistance of thermistor decreases
1
therefore the current in the circuit increases
1
causing a bigger share of the p.d. across 6 Ω resistor
1

(ii)     0 – 100 (°C)
accept 10° – 100°C
1

(iii)     20°C to 40 °C
1
because a small temperature change gives a bigger
voltmeter reading change
1

(c)     thermostat
accept a correct description of a use
1
[11]
 M3.          (i)      30
allow 1 mark for showing correct method i.e. 5 × 6 or 12 ÷ 0.4
2
(ii)      connected in series
insufficient they are not connected in parallel
1
(iii)     0.4
1
(iv)     equally/ evenly
the same is insufficient
allow credit for candidates that correctly mention pd across the connecting wires
accept (nearly) 2 V (each)
1
[5]
 M4.          (a)     (i)      4 (V)
allow 1 mark for correct substitution
2

(ii)     5 (V) or (9 – their (a)(i)) correctly calculated
e.c.f
do not allow a negative answer
1

(b)     (i)      thermistor
c.a.o
1
(ii)     0°C to 20°C
1
[5]
 M5.          (a)     all symbols correct

accept push switch symbol switch may be open or closed
any lines through symbols = 0 marks
1
          correct circuit drawn
polarity of cells not relevant provided they are joined correctly
1
          voltmeter must be across resistor only
two cells are required in the diagram
ignore the order of the components
allow small gaps in circuit
omission of any component = 0 marks
1

(b)     (i)      potential difference  = current × resistance
accept voltage or p.d. for potential difference
accept V= I × R 
accept  provided I R subsequent use correct
 
do not accept C for current
1

(ii)     2
allow 1 mark for correct substitution
wrong working loses both marks
2
(iii)     straight line drawn through the origin
judge by eye
         straight line passes through I = 0.4, V = their (b)(ii) / 2 and 0.0
this mark may be awarded if all points shown including these points are correct even if no line is drawn
N.B. a curve scores 0 marks
1

(c)     temperature increases
accept filament lamp / it gets hotter
allow heat for temperature
1
[8]

 
M6.          (a)     C
award mark if A and B identified as not filament lamp
1
resistance increases
negated by wrong statement e.g. current goes down
1

as the lamp gets hot
accept as current (through lamp) or voltage (across lamp) increases
do not accept non-ohmic reason independent of choice of component
1

(b)     ammeter wire and battery only in series
non standard symbols acceptable if correctly identified (labelled) for ammeter, voltmeter and battery
1

          voltmeter only in parallel with wire or battery
all in series or ammeter in parallel neither of these two marks awarded
1
all symbols correct
ignore lines drawn through centres of symbols
1

          (c)     (i)      voltage = current × resistance
accept V = I × R
accept volts = amps × ohms
do not accept V = C × R
accept 

if subsequent method correct
1

(ii)     30
accept correct substitution for 1 mark (9/0.3)
2
         ohms
accept correct symbol Ω
1

(iii)     goes up
must be a comparison
accept calculation if answer is larger than c (ii)
1
[11]
 M7.          (a)     (i)      the lamp will be on/will give out light
1
(ii)     the lamp will be off/will not give out any light
1

(b)     (very) large current flows
or damage the battery/overheat the battery
or short circuit
or wire get hot
1

(c)     switch connected in series with lamp and battery
1
[4]
 
M8.          (a)     4 symbols correct accept
(accept  for bulb; lose 1 mark if line through symbols, lose 1 mark if circuit incorrect, switch may be open or closed)
(allow  or )
gains 1 mark
4

          but
all correct
gains 2 marks
          ammeter in series with lamp
for one mark
          voltmeter in parallel with lamp / lamp and switch / lamp, switch and ammeter
for one mark

(b)     (i)      5 points correctly plotted
allow (0, 0) correct if graph goes through the origin even if no × or O
gains 1 mark
         but
6 points correctly plotted
gains 2 marks
         smooth curve through points – not straight line / curve + straight line
for one mark
3

(ii)     2 (A)
         allow  0.05 (½ square) from candidates’ graph
for one mark
1

(iii)     R = V / I   or   R = 10 / 2
gains 1 mark
         but
R = 5 (Ohms)      ecf
gains 2 marks
2

(c)     (i)      resistance increases
for one mark
(ii)     temperature (of filament) has increased / filament gets hot
for one mark
2
[12]
 M9.          (a)     series circuit
all four components must be included
if a battery included the neatness mark may still be awarded
1
          circuit fully functional or properly connected
this is the neatness mark
do not credit a parallel circuit with one switch controlling both components
1

(b)     case or outer parts are made of plastic or insulator or non-metallic
1
          there is no electrical pathway between inner and outer insulation
accept no connection between inner and outer part
do not credit two layers of insulation
1

(c)     (i)      [A]    power = voltage × current
accept P = V I or
          W = V × A
or any transformation
1
[B]     1600 ÷ 230 =current
1
          6.96 or 7
accept with no working for two marks
accept 6.95
in [A] award a mark for a triangle if calculation correctly performed
1

(ii)     [A]    voltage = current × resistance
accept V = I R or any transformation
1
[B]     230 ÷ 7 = overall R = 33
accept 230 ÷ 6.96 = overall R = 33
1
         resistance of motor = 33 – 20 = 13
accept with no working for two marks 
do not credit negative answer
accept consequential errors from c(i)
in [A] award a mark for a triangle if calculation correctly performed
1
[10]
 M10.          (a)     current rises/starts lower/starts from zero
for 1 mark
          ideas that: *
smaller/only 0.45 (A) change in current
quicker/only 2 (ms) for current to settle
slightly lower/0.45 (A) final current
maximum only 0.45 (A) rather than 1.5 (A)
(*must compare e.g. “only...” or state figure from first graph)
any 2 for 1 further mark each
3

(b)     resistance of filament rises as temperature rises/higher at operating temperature    
resistance of X falls as temperature rises/low(er) at operating temperature
total resistance stays roughly the same as temperature rises
so current stays roughly the same as temperature rises
(must be related to previous point)

          resistance of X falls faster at first than resistance of filament rises
so current rises (must be related to previous point)
operating resistance slightly increased
so operating current slightly reduced
(must be related to previous point)
resistance of X high at start
so current zero/low
each gains 1 mark
(must be related to previous point)
(to a maximum of 4)
4
[7]