A fuse in electric circuit is rated 4 A. Can it be used with an electric heater of rating 2 kW, 200 V ? Explain your answer.
Generated by claude-sonnet-4-6 · 2026-06-15 06:41 · grounding rag
Model Answer
Current drawn by the heater:
$$I = \frac{P}{V} = \frac{2000 \text{ W}}{200 \text{ V}} = 10 \text{ A}$$
The heater requires 10 A, but the fuse is rated only 4 A. Since the current through the circuit (10 A) is much greater than the fuse rating (4 A), the fuse will blow immediately. Therefore, a 4 A fuse cannot be used with this heater.
Source: Chapter 11, Section 11.7.1
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Explanation
- Examiners expect you to calculate the current using $I = P/V$ — this is the key step that earns marks.
- Then compare the calculated current with the fuse rating and give a clear conclusion.
- The textbook example (1 kW iron at 220 V → 4.54 A → use 5 A fuse) follows the same logic; here 10 A >> 4 A, so the fuse is inadequate.
- Do not just state "no" without the calculation — that will lose a mark.