Question

A fuse is used in an electric circuit to
(A) Break the circuit when excessive current flows through the circuit
(B) Break the circuit when power gets off
(C) Indicate if the current is flowing uninterrupted
(D) Complete the circuit for the flow of current

Answer 1

Hint: A fuse is used in electric circuits to protect some equipment or a series of equipment from damage due to excessive current. A fuse is placed before the appliances in the live wire such that first the fuse would get excited and then the power would flow to the appliances in series with the fuse. In case of excessive current being drawn, the fuse melts due to overheating, thus breaking the circuit.

Complete Step by step solution:
The main purpose of a fuse is to break the circuit to prevent damage to any appliance connected after the fuse. The properties of the wires used in a fuse are:
-They should be made of materials with a low melting point so that when excessive current flows, the fuse wire would melt disrupting the circuit.
-The material used in a fuse wire should also have a low ohmic loss and high conductivity so that a thin wire can also pass current with less resistance.
Fuse can also be termed as a low resistance resistor acting as a sacrificial device to provide overcurrent protection. Thus when current exceeds the permissible limit of an appliance according to which the fuse is designed, the fuse wire melts causing disruption in the flow of current. This protects the appliance possibly from damage by switching it off altogether.
The correct answer is option (A) Break the circuit when excessive current flows through the circuit.

Note:
Nowadays, even in residential households, fuses have been replaced with miniature circuit breakers. Miniature circuit breakers are automatically operated switches which protect low voltage electric circuits from excess currents due to overload or short circuit.