Question

The material of fuse wire should have
(A) A high specific resistance and high melting point
(B) A low specific resistance and low melting point
(C) A high specific resistance and low melting point
(D) A low specific resistance and high melting point

Answer 1

Hint : In order to solve this question, we need to understand that a fuse wire is used in a circuit to check the current in the circuit. It works on the principle of Joule’s law of heating. If a very high current (which can damage other components in the circuit) flows through the fuse wire, a lot of heat is generated and this causes the fuse wire to melt and break the circuit.
The Joule’s law of heating states that the heat produced per second $H$ in a wire of resistance $R$ carrying a current $I$ is given by,
$H = {I^2}R$

Complete Step By Step Answer:
The fuse is a safety element that is put in series at the start of an electrical circuit to check the overload of current in it. If there is an overload of current flowing in the circuit, other electrical components in the circuit may get damaged.
The fuse prevents this by implementing the principle of Joule’s law of heating.
The Joule’s law of heating states that the heat produced per second $H$ in a wire of resistance $R$ carrying a current $I$ is given by,
$H = {I^2}R - - - (1)$
If the current $I$ flowing is very high, a lot of heat is generated in the fuse wire and this causes the wire to melt and thus break the circuit, thereby stopping the flow of the overload current.
A fuse wire should have a high resistance so that according to (1), a lot of heat is generated and it is easier for the fuse wire to reach its melting point. Also, a high resistance decreases the current flowing in the circuit than what would have been in the absence of it.
Also, a fuse wire should have a low melting point so that it can be reached easily and the fuse wire can break by melting. If the melting point is too high, it will take a lot of current for a long period of time for the fuse to reach its melting point and break. In the meantime, the high current can damage the other electrical components.
Hence, the correct option is (C).

Note :
Students must remember that though the fuse wire has high resistance, it is usually made of material of low resistivity or high conductivity such as metals like aluminium and tin. The material has high conductivity, so that there is an easy flow of electric current through the wire. However, the resistance is made high by virtue of the dimensions or shape of the wire such as high length and low cross-sectional area. Students thus might get confused by the property of low resistivity of the material and think thus, that the fuse wire must also have low resistance.