Safety devices
3 marks · NormalAn electric fan develops a fault and starts drawing a current much higher than normal. It is fitted with a fuse in the plug.
Explain how the fuse protects the circuit and user in this situation.
Describe what must be done before the fan can be used again after the fuse blows.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) When the current becomes too high, the thin wire inside the fuse heats up and melts. This breaks the circuit and stops current flowing, protecting both the circuit and the user from damage or electric shock.
(b) The blown fuse must be replaced with a new fuse of the same rating before using the fan again.
Also accept: fuse must be replaced with same rating
Common mistakes: Saying a bigger fuse should be used after blowing; Not stating fuse must be replaced
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · States fuse melts when current is too high.
A1 (a) · 1 mark · States this action breaks the circuit and protects the device/user from electric shock or damage.
B1 (b) · 1 mark · States that the fuse must be replaced with one of the same rating before the fan is used again.
Worked solution
a) If the fan draws a current much higher than normal, the fuse wire heats up and melts (blows). This breaks the circuit and stops electricity from reaching the fan, protecting it from overheating or catching fire and also protects the user from possible electric shock.
b) The blown fuse must be replaced with a new fuse with the same rating before safely using the fan again.