Explain in brief the function of an electric fuse in a domestic circuit. An electric heater of current rating 3 kW; 220 V is to be operated in an electric circuit of rating 5 A. What is likely to happen when the heater is switched 'ON'? Justify your answer with necessary calculation.

Function of an Electric Fuse

An electric fuse is a crucial safety device used in domestic circuits to protect electrical appliances and wiring from damage caused by excessive current (overloading or short-circuiting). It consists of a wire made of a metal or alloy with a low melting point and high resistance. When the current flowing through the circuit exceeds a safe limit, the fuse wire heats up, melts, and breaks the circuit, thereby stopping the flow of current.

Calculation and Justification

Given:

• Power rating of the electric heater, $P = 3\text{ kW} = 3000\text{ W}$
• Operating voltage, $V = 220\text{ V}$
• Current rating of the circuit, $I_{\text{limit}} = 5\text{ A}$

Using the electric power formula:

$$P = V \times I$$

We can calculate the current $I$ drawn by the heater:

$$I = \frac{P}{V}$$

Substituting the given values:

$$I = \frac{3000\text{ W}}{220\text{ V}} \approx 13.64\text{ A}$$

Conclusion

The current drawn by the electric heater ($13.64\text{ A}$) is significantly greater than the current rating of the circuit ($5\text{ A}$).

When the heater is switched 'ON', it will draw an excessively high current of $13.64\text{ A}$. This will cause overloading in the circuit. Consequently, the fuse wire in the circuit will heat up, melt, and break the circuit (or trip the circuit breaker) to prevent any fire hazard or damage to the wiring.