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GCSE Physics · key term
A safety device that automatically opens a switch when the current becomes dangerously large.
Used by Edexcel
Specification 10.38, 10.41 · Paper 2
Revise: Earth Wire and FusesThe earth wire provides the route; a fuse or circuit breaker disconnects the circuit.
A safety switch that automatically opens a circuit when it detects an excessive current.
Trace the fault sequence in order: live wire touches the metal case → a large current flows through the earth wire → the fuse melts or the circuit breaker trips → the supply is disconnected.
Distinguish the devices clearly: a fuse must be replaced after its wire melts, whereas a circuit breaker opens a switch and can be reset.
Distinguish the two cases clearly: a person forming the path risks electrocution, whereas a low-resistance earth wire carries a fault current so that a fuse or circuit breaker disconnects the supply.
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