**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)**