Practice Questions

1.Explain how a fuse works as a safety device

A fuse is a thin piece of wire that the current flows along. The fuse wire will only allow a maximum current to flow. If the appliance becomes faulty and draws a large current, then the fuse wire will become hot, melt and break the circuit. 

2. A hair dryer uses 1100W and 230V whilst switched on. 

(a) Calculate the normal current that the hairdryer would use

P = V x I

I = P/V

I = 1100/230 = 4.8A

(b) Fuses have ratings of 3A, 5A or 13A. Which fuse should be placed into the plug of the hair dryer?

The appliance uses 4.8 A for normal operation, so a 5 A fuse should be used. 

3.Ben is using his radio to listen to music, the fuse blows in the radio. Ben doesn’t have a 3A fuse to replace the one that is broken. However, he does have a 13A fuse. Explain why it would be unsafe to use the 13A fuse to replace the broken 3A fuse.

The appliance would still work with the 13A fuse. However, this would be dangerous because if the appliance becomes faulty, the fuse wire will not melt until the current reaches 13A, instead of 3A. This means that the wires will become hotter and there is a greater risk of an electrical fire.