Working of safety fuses depends upon magnetic effect of the current

Working of safety fuses depends upon

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magnetic effect of the current
chemical effect of the current
magnitude of the current
heating effect of the current

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This question was previously asked in

UPSC CDS-1 – 2018

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A safety fuse is designed to protect electrical circuits from overcurrents. It consists of a wire made of a material with a low melting point (like tin-lead alloy) and a specific resistance. When the current flowing through the wire exceeds a safe limit (the fuse rating), the wire heats up significantly due to the **heating effect of the current** (Joule heating, H = I²Rt). If the **magnitude of the current** is sufficiently high, the heat generated melts the fuse wire, breaking the circuit and stopping the flow of current. Therefore, the working of a safety fuse depends on the magnitude of the current and its heating effect.

– The heating effect of electric current states that heat is produced when current flows through a resistance.
– The amount of heat produced is proportional to the square of the current (I²), the resistance (R), and the time (t).
– Fuse wire melts when the heat generated by excessive current raises its temperature to its melting point.
– The specific melting current is determined by the material, length, and thickness of the fuse wire.

Magnetic effect of current is used in devices like circuit breakers which use an electromagnet to trip a switch when current exceeds a limit. Chemical effect of current is associated with electrolysis. Neither magnetic nor chemical effects are the primary working principles of a simple fuse wire melting due to overcurrent. Only the magnitude of current (as it determines the heat) and the heating effect are relevant.

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