Questions

Q1.

(a) A technician investigates a light-dependent resistor (LDR) connected in series with a 120 Ωresistor and a voltage source.

The technician measures the voltage across the LDR and also the current in the LDR.

(i) Which one of these circuits should the technician use?

Put a cross ( ) in the box next to your answer.

(1)

(ii) When the LDR is in bright sunlight, its resistance is 185 Ω.The voltage across the LDR is then 7.2V.

Show that the current in the LDR is about 0.039 A.

(2)

(iii) Complete the sentence by putting a cross ( ) in the box next to your answer.

The current in the 120 Ω resistor is

(1)

A much more than the current in the LDR

B much less than the current in the LDR

C the same as the current in the LDR

D the opposite of the current in the LDR

(iv) The technician repeats the readings with the LDR in different light conditions.

The table gives two of the readings.

Explain why the two current readings are different.

(2)

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*(b) The photograph shows a temporary traffic sign.

The traffic sign uses many small lights all powered by a rechargeable battery.These lights need to be very bright during the day so that they can be seen clearly.They do not need to be as bright at night.

Explain how using a light-dependent resistor can make the energy stored in the battery lastlonger.

(6)

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Q2.

An inventor is designing a battery-powered torch.She wants the torch to have a brightness control.

(a) Which of these could she use in this control?

Put a cross ( ) in the box next to your answer.

(1)

A a diode

B a light-dependent resistor

C a thermistor

D a variable resistor

(b) She builds this circuit to test the lamp in the torch.

(i) Add a voltmeter to the circuit which will measure the potential difference (voltage)across the lamp.

(1)

She sets the control at the "bright" position.The current is 0.26 A and the potential difference (voltage) across the lamp is 6.0 V.

Calculate the resistance of the lamp.

(2)

resistance of the lamp = . . . . . . . . . . . . . . . . . . . . . . Ω

(c) The inventor takes readings of the potential difference (voltage) across the lamp and thecurrent at different positions of the control from "dim" to "bright".

She plots a graph of the readings.

(i) Complete this graph by plotting the missing point and drawing the curve of best fit.

(2)

(ii) Describe what this graph shows about how the current changes as the voltagechanges.

(2)

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(iii) The lamp gives no light when the brightness control is at its lowest setting.

Suggest why the torch would still need an on/off switch as well as the brightness control.

(2)

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(Total for Question = 10 marks)

Q3.

A student is investigating a filament lamp.

(a) (i) Complete the sentence by putting a cross ( ) in the box next to your answer.

The current in the filament lamp is a flow of

(1)

A protons

B neutrons

C electrons

D atoms

(ii) The student uses this circuit in his investigation.

State what is measured by the meters.

(2)

Meter 1 measures.............................................................................................................................................

Meter 2 measures.............................................................................................................................................

(b) The normal operating potential difference (voltage) and current of the filament lamp is 6 V,

0.4 A.

Calculate the energy supplied to the lamp under these conditions in 20 s.

(2)

energy = ........................................................... J

(c) The graph shows how current varies with potential difference (voltage) for another filamentlamp.

Calculate the resistance of the lamp when the current in the lamp is 0.3 A.

resistance = potential difference ÷ current (R = V / I)

(3)

resistance = ........................................................... Ω

(Total for Question = 8 marks)

Q4.

An inventor is designing a battery-powered torch.She wants the torch to have a brightness control.

The inventor takes readings of the potential difference (voltage) across the lamp and thecurrent at different positions of the control from "dim" to "bright".

She plots a graph of the readings.

(i) Complete this graph by plotting the missing point and drawing the curve of best fit.

(2)

(ii) Describe what this graph shows about how the current changes as the voltagechanges.

(2)

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(iii) The lamp gives no light when the brightness control is at its lowest setting.

Suggest why the torch would still need an on/off switch as well as the brightness control.

(2)

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Q5. The photograph shows a device used to measure the amount of light.

The circuit diagram shows how the components inside this device are connected.

(i) Complete the sentence by putting a cross ( ) in the box next to your answer.

The meter used in this circuit is

(1)

A a voltmeter connected in series with the LDR

B a voltmeter connected in parallel with the LDR

C an ammeter connected in series with the LDR

D an ammeter connected in parallel with the LDR

(ii) The amount of light entering the light-dependent resistor (LDR) increases.

Which row of the table correctly describes the change in the resistance of the LDR and the

change in the current in the circuit?

Put a cross ( ) in the box next to your answer.

(1)

resistance of the LDR current in circuitA increases decreasesB increases increasesC decreases decreasesD decreases increases

(iii) The device is used as a light meter.

It has a 9 V battery.

Calculate the current when the resistance of the LDR is 600 Ω.

(3)

current = ........................................ A

(iv) When the light meter has been used for a long time, the meter reading becomes incorrect.

Suggest what has happened.

(2)

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Q6.

(a) The diagram shows an electric circuit with two resistors, R and S.

(i) R has a resistance of 11 ohms.

Calculate the potential difference across R.

(2)

potential difference = . . . . . . . . . . . . . . . . . . . . . . V

(ii) Use information from the diagram to calculate the current in S.

(1)

current = . . . . . . . . . . . . . . . . . . . . . . A

(iii) Complete the sentence by putting a cross ( ) in the box next to your answer.

A student wants to measure the battery voltage with a voltmeter.

The voltmeter should be placed

(1)

A in series with the battery

B in parallel with the battery

C in parallel with the ammeter

D in series with either resistor R or S

(b) Explain why the temperature of a resistor increases when a current passes through it.

(2)

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*(c) A resistor is a circuit component.

Two other circuit components are a light dependent resistor (LDR) and a thermistor.

Explain how LDRs and thermistors can be used to control the current in a circuit.

(6)

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(Total for Question is 12 marks)

Q7.

(a) A designer is going to use a thermistor in a temperature gauge. He connects the thermistorinto this circuit.

He heats the thermistor and measures the current at different temperatures. Here aresome of the results plotted on a graph.

At 47 °C the current was 0.138 A.

(i) Plot this value on the graph.

(1)

(ii) Draw the curve of best fit through the points.

(1)

(iii) The supply voltage is 12 V. At 20 °C the current is 0.047 A.

Calculate the resistance of the thermistor at this temperature.

(3)

resistance = . . . . . . . . . . . . . . . . . . . . . . Ω

(iv) Use this graph of current against temperature to explain the relationship betweenresistance and temperature for this thermistor.

(2)

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(b) (i) When there is an electric current in a resistor, the resistor gets hot.

Explain why the resistor gets hot.

(2)

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(ii) Suggest why the thermistor in a temperature gauge might indicate a temperatureslightly higher than the actual temperature of its surroundings.

(1)

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(Total for Question = 10 marks)

Mark Scheme

Q1.

Q2.

Answer Acceptable answers Mark(a) D a variable resistor (1)

(b)(i)

connected in parallel with lamp (1)

recognisable symbol such as a boxwith letter V inside or box with theword voltmeter inside it acceptvoltmeter across both lamp andammeter

(1)

(b(ii) SubstitutionR = 6.0 / 0.26 (1) An answer which rounds to 23

(2)

Evaluation= 23 (1)

Give full marks for correct answer noworking

(c)(i) point correctly plotted at 2.0, 0.14 towithin half a small square (1)

smooth curve of best fit connecting allgiven points within half a small square(1)

Judge curve by eye.If more than one line present thenignore any that appear to be erased ordeleted.Ignore any part of line which goesbeyond given points.If plotted point is incorrect then allowecf for line

(2)

(c)(ii) a description includingtwo of thefollowing:

current increases as voltageincreases (1)

current is not proportional tothe pd (1)

gradient gets less (1)

Allow reverse argument

positive correlation (between them )

graph is not a straight line not in equalsteps

current does not increase as much (asit gets higher)

accept resistance has increased withincrease in current for two marks

(2)

(c)(iii) a suggestion to include:

there is still a current (when control isat min position) (1)

make the battery last longer (1)

to break the circuitto switch the currentoff accept flowofelectricity/charge/electrons for current

battery / energy would be drained/used up/ wasted otherwise acceptreverse arguments

ignore reference to power / volts

(2)

Q3.

Q4.

Answer Acceptable answers Mark(i) point correctly plotted at 2.0, 0.14 to

within half a small square (1)

smooth curve of best fit connecting allgiven points within half a small square(1)

Judge curve by eye.If more than one line present thenignore any that appear to be erased ordeleted.Ignore any part of line which goesbeyond given points.If plotted point is incorrect then allowecf for line

(2)

(ii) a description includingtwo of thefollowing:

current increases as voltageincreases (1)

current is not proportional tothe pd (1)

gradient gets less (1)

Allow reverse argument

positive correlation (between them )

graph is not a straight line not in equalsteps

current does not increase as much (asit gets higher)

(2)

accept resistance has increased withincrease in current for two marks

(iii) a suggestion to include:

there is still a current (when control isat min position) (1)

make the battery last longer (1)

to break the circuitto switch the currentoff accept flowofelectricity/charge/electrons for current

battery / energy would be drained/used up/ wasted otherwise acceptreverse arguments

ignore reference to power / volts

(2)

Q5.

QuestionNumber

Answer Acceptable answers Mark

(i) C (1)

QuestionNumber

Answer Acceptable answers Mark

(ii) D (1)

QuestionNumber

Answer Acceptable answers Mark

(iii) substitution (1)

9 = I × 600

transposition (1)

I = 9/600

evaluation (1)

= 0.015 (A)

OR

=15 mA

allow substitution andtransposition in either

order

give full marks forcorrect answer, no

working

(3)

QuestionNumber

Answer Acceptable answers Mark

(iv) An explanation linkingthe following

(2)

• battery voltage hasdecreased (1)

• (so) less current(than expected) (1)

Q6.

Answer Acceptable answers Mark

(a)(i)

11x 0.4 (substitution)(1)

4.4 (V)(1)

Full marks for correct answer withno calculation

(2)

(a)(ii) 0.6 - 0.4 (A)(1)

0.2 or 1/5 (A) (1)

(a)(iii) B (1)(b) An explanation linking: electrons

(1)

colliding with / bumping intoions in the lattice /atoms in themetal (1)

colliding with other electrons

If no other marks scored, allowfor 1 mark for "electrical energytransferred/changed intothermal/heat energy"

do not allow energy beingcreated or produced

(2)

Indicative Content MarkQWC *(c) A explanation including some of the following points

Light dependent resistors (LDR)

Resistance changes with light intensityBright light , low resistanceNo light (dark), high resistanceLow resistance gives high current.(RA)

Thermistor

Resistance changes with temperatureNegative temperature coefficientHigh temperature, low resistanceLow temperature, high resistanceLow resistance gives high current (RA)

(6)

Level 0 No rewardable content1 1 - 2 a limited explanation linking light affecting LDR AND heat affecting

thermistorOR a correct relationship for one device, e.g. thermistors change

resistance when the temperature changes and LDRs changeresistance when it gets dark OR the resistance decreases/ currentincreases of a LDR when the light gets brighterthe answer communicates ideas using simple language and useslimited scientific terminologyspelling, punctuation and grammar are used with limited accuracy

2 3 - 4 a simple explanation correctly linking the temperature and light withresistance or current for both devicesOR a correct relationship for one device with a link to the way thisaffects the current and resistance.e.g. the resistance of a LDR increases when the light gets dimmer andwhen the temperature lowers the resistance of a thermistor increasesOR the resistance of a LDR decreases when the light gets brighterand this increases the currentthe answer communicates ideas showing some evidence of clarityand organisation and uses scientific terminology appropriatelyspelling, punctuation and grammar are used with some accuracy

3 5 - 6 a detailed explanation including the qualitative relationships for bothdevices and a link to the way resistance change affects the current inBOTH of them, e.g. the resistance of a LDR is less when the light getsbrighter which increases the current. When the temperature lowersthe resistance of a thermistor increases. This means that the currentwill decrease as the thermistor cools down.the answer communicates ideas clearly and coherently uses a rangeof scientific terminology accuratelyspelling, punctuation and grammar are used with few errors

Total for question = 12 marks

Q7.

Answer Acceptable answers Mark(a)(i) Correctly plotted point (1) +/- ½ a small square (1)(a)(ii) Smooth line through most (at least 5)

crosses / points (1)

Do not accept clearly dot-to-dot orexcessive tramliningIgnore any part of line after 45

(1)

(a) (iii) Substitution: (1)

12 = 0.047 × R

Transposition: (1)

R = 12/0.047

Evaluation: (1)

R = 260

transposition and substitution in eitherorder

substitution mark can be scored whenincorrectly transposed word/symbolequation is given

255.3, 255give full marks for correct answer noworkingpower of 10 errors with noworking score max 1 mark

(3)

(a) (iv) An explanation linking

current increases withtemperature (1)

with

(so) resistance decreases(1)

or

the voltage is constant (1) with

(so) resistance decreases (withtemperature increase)(1)

(for this first MP)ignore faster/slower(charge/current)

ignore references to heat, current flows more

can score both marks by quoting twosuitable pairs of values from graph

For full marks, there must be areference to change of either I or Rwith temperature

(2)

(b)(i) An explanation linking

electrons / negative charges(1)

collide withions/lattice/electrons (1)

atoms / nuclei

allow for 1 mark,electrical energytransferred to thermal/heat energyif no other scored

(2)

(b) (ii) A suggestion including

energy transfer in the thermistor/any component part of the electricalcircuit causes a rise in temperatureof thermistor (above surroundings)(1)

thermistor/resistor gets hot/isheated

(1)

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