GCSE Standard Questions: Electric Circuits

Q9. Here is an LED torch.

(a) The torch contains one LED, one switch and three cells.

Which circuit diagram shows the correct circuit for the torch?

[1 mark]

(b) Write down the equation which links charge flow (Q), current (I) and time (t).

[1 mark]

(c) The torch worked for 14,400 seconds before the cells needed replacing.

The current in the LED was 50 mA.

Calculate the total charge flow through the cells.

[3 marks]

(d) When replaced, the cells were put into the torch the wrong way around.

Explain why the torch did not work.

[2 marks]

(e) Write down the equation which links efficiency, total power input and useful power output.

[1 mark]

(f) The total power input to the LED was 0.24 W.

The efficiency of the LED was 0.75

Calculate the useful power output of the LED.

[3 marks]

(Total 11 marks)