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Question
How is Joule's law effect useful in electric circuits where fuse is used as a safety device?
Solution
Joule’s heating is the fuse used in electric circuits. It protects circuits and appliances by stopping unduly high electric current flow. The fuse is placed in series with the device. It consists of a piece of wire made of a metal or an alloy of appropriate melting point, for example, aluminium, copper, iron, lead, etc. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit. The fuse wire is usually encased in a cartridge of porcelain or similar material with metal ends. The fuses used for domestic purposes are rated as 1 A, 2 A, 3 A, 5 A, 10 A, etc.
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