MAINS ELECTRICITY
4 marks · NormalA hairdryer is connected to the mains. The diagram shows a simplified circuit with a fuse.
Name two energy transfers that take place when the hairdryer is used.
Explain what happens to the fuse if the heating element develops a short circuit.
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) Electrical energy is transferred to thermal (heat) energy and to kinetic energy (if the hairdryer has a fan).
(b) A short circuit causes a large current to flow through the fuse, which then heats up and melts, breaking the circuit.
Must show: energy transfer terms, current/fuse relationship
Also accept: Electrical -> thermal, electrical -> kinetic (fan)
Common mistakes: Wrong order of energy, omitting fuse explanation
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States electrical energy is converted to thermal (heat) energy.
B1 (a) · 1 mark · States electrical energy is converted to kinetic energy or vice versa.
M1 (b) · 1 mark · States that a large current flows if there is a short circuit.
A1 (b) · 1 mark · Explains the fuse melts/breaks the circuit to prevent damage or further hazard.
Worked solution
a) Electrical energy is transferred to heat energy (to dry hair) and to kinetic energy (the fan inside the hairdryer spins to blow air).
b) If a short circuit develops, the current through the fuse increases greatly. The fuse wire heats up and melts, disconnecting the circuit and preventing further damage or hazard.