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GCSE Standard Questions: Electric Circuits

Q8. Marion investigated how the current in a filament lamp varied with the potential difference across the filament lamp.

(a) This shows part of the circuit used:

Complete the circuit by adding an ammeter and a voltmeter. (Use the correct circuit symbols).

correct ammeter and voltmeter symbols

voltmeter in parallel with lamp

ammeter in series with lamp

[3 marks]

(b) Here is a graph showing some of the results:

Marion then reversed the connections to the power supply and obtained negative values for the current and potential difference.

(i) Draw a line on the graph above to show the relationship between the negative values of current and potential difference.

smooth curved line of correct shape

passing through - 4.0 V, - 0.2 A or – 6.0 V, - 0.23 A

[2 marks]

(ii) Write down the equation which links current (I), potential difference (V) and resistance (R).

potential difference = current × resistance

V = IR

[1 mark]

(iii) Using the data from the graph, determine the resistance of the filament lamp when the potential difference across it is 1.0 V.

V = 1.0 V

I = 0.08 A (from graph)

V = IR

1.0 = 0.08 x R

R = 1.0/0.08

R = 12.5 Ω

[4 marks]

(c) Robin did the same investigation. The ammeter he used had a zero error.

What is meant by a zero error?

That the ammeter displays a reading when not connected to a circuit.

[1 mark]

(Total 11 marks)