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GCSE Standard Questions: Electric Circuits

Q2. A student investigated how the resistance of a piece of nichrome wire varies with length. The diagram shows part of the circuit that the student used.

Copy the circuit in the space below, adding an ammeter and a voltmeter so that the resistance of the wire can be calculated. Be careful to use the correct symbols.

ammeter and voltmeter symbols correct

voltmeter in parallel with wire

ammeter in series with wire

[3 marks]

(b) Describe how the student would obtain the data needed for the investigation. Your answer should include a risk assessment for one hazard in the investigation.

This type of question is marked in two ways:

- the examiner looks for relevant instructions

- but also for the correct order - and any opposing instructions make you lose marks!

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

The method would lead to the production of a valid outcome. All key steps are identified and logically sequenced.

5 - 6 marks
Level 2: The method would not necessarily lead to a valid outcome. Most steps are identified, but the method is not fully logically sequenced.
3 - 4 marks
Level 1: The method would not lead to a valid outcome. Some relevant steps are identified, but links are not made clear.
1 - 2 marks
Level 0: No relevant content.
0 marks

 

Indicative content they looked for:

length measured

length varied

current measured

potential difference measured

repeat readings

calculate resistance for each length

resistance = potential difference/current

plot a graph of resistance against length

hazard: high current

may cause wire to melt / overheat

may cause burns (to skin)

so use low currents

[6 marks]

 

(c) Why would switching off the circuit between readings have improved the accuracy of the student's investigation?

Tick one box.

Reason Tick here
The charge flow through the wire would not change.  
The potential difference of the battery would not increase.  
The power output of the battery would not increase.  
The temperature of the wire would not change.

[1 mark]

(d) The students used crocodile clips to make connections to the wire.

They could have used a piece of equipment called a 'jockey'.

The photo below shows a crocodile clip and a jockey in contact with a wire.

How would using the jockey have affected the accuracy and resolution of the student's results compared to using the crocodile clip?

Tick two boxes.

Reason Tick here
The accuracy of the student's results would be higher.
The accuracy of the student's results would be lower.  
The accuracy of the student's results would be the same.  
The resolution of the length measurement would be higher.
The resolution of the length measurement would be lower.  
The resolution of the length measurement would be the same.  

 

The jockey gives a clearer reading than the croc-clip as it has a fine 'contact point'.

[2 marks]

(Total 12 marks)