An electric heater rated 1100 W operates at 220 V. Calculate (i) its resistance, and (ii) the current drawn by it.
Generated by claude-sonnet-4-6 · 2026-06-15 06:45 · grounding rag
Model Answer
Given: Power P = 1100 W, Voltage V = 220 V
(i) Resistance:
Using $P = \dfrac{V^2}{R}$,
$$R = \frac{V^2}{P} = \frac{(220)^2}{1100} = \frac{48400}{1100} = \mathbf{44 \ \Omega}$$
(ii) Current:
Using $P = VI$,
$$I = \frac{P}{V} = \frac{1100}{220} = \mathbf{5 \ \text{A}}$$
Source: Chapter 11, Section 11.8 Electric Power
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Explanation
- Examiners expect both formulae to be stated before substitution — never just write the answer.
- Two ready formulae work here: $R = V^2/P$ and $I = P/V$. Alternatively, find R first via $R = V^2/P$, then use Ohm's law $I = V/R$. Either route is acceptable.
- Each sub-part carries 1 mark: 0.5 for the correct formula/substitution and 0.5 for the correct numerical answer with unit.