Ans:
Fuse is a protective device, which consists of a thin wire or strip. This wire or strip is placed
with the circuit it has to protect, so that the circuit-current flows through it. When this current
is too large, and heat produced due to I2Rt exceeds the melting point of the fuse,
consequently fuse wire or strip melts thus breaking the circuit and interrupting the power
supply.
A fuse material should possess the following properties;-
Low resistivity – This means, thin wires can be used, which will give less metal vapour after
melting of the wire. Less metal vapour in the arc gives lower conductivity and thus makes
quenching of arc easier.
Low conductivity of the metal vapours itself.
Low melting point- This means that the temperature of the fuse material for normal currents
stays at a low value. Previously lead was used as fuse material because of its low melting
point but thick wires of lead are required due to higher resistivity. For rewireable fuses alloys
of tin and lead or tinned copper wires are commonly used. In caridge fuses silver and silver
alloys are used of lower ratings. Copper alloys are used in fuses of higher ratings.