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.
Generated by claude-sonnet-4-6 · 2026-06-15 06:46 · grounding rag
Model Answer
Function of Electric Fuse: A fuse protects circuits and appliances by stopping the flow of unduly high electric current. It consists of a low-melting-point wire connected in series. If current exceeds the rated value, the fuse wire heats up, melts, and breaks the circuit.
Calculation:
Current drawn by heater:
$$I = \frac{P}{V} = \frac{3000 \text{ W}}{220 \text{ V}} \approx 13.6 \text{ A}$$
The circuit is rated for only 5 A, but the heater draws 13.6 A, which far exceeds the circuit rating.
Result: When switched ON, the fuse wire will melt and break the circuit, cutting off the supply to prevent damage or fire.
Source: Chapter 11, Section 11.7.1
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Explanation
- The fuse function fetches 1 mark — keep it to 2–3 lines mentioning: series connection, melting point wire, excess current → melts → breaks circuit.
- The calculation fetches 2 marks: use $I = P/V$, compare with 5 A rating, and state the consequence clearly.
- Examiners expect the formula, substitution, result (≈13.6 A), and the conclusion that the fuse will blow — all four steps for full marks.