Question

Sol. [Key Concept: Heater power P ∝ V² at fixed resistance] Rated power of heater $\begin{array}{r} P_{0} = \frac{V_{0}^{2}}{R}\#(i) \end{array} $$$ {Consumed\ power }{\begin{array}{r} P_{c} = \frac{V^{2}}{R}\#(ii) \end{array} } {From\ (i)\ and\ (ii) } \begin{matrix} & \frac{P_{c}}{P_{0}} = \frac{V^{2}}{V_{0}^{2}} \\ & P_{c} = \left\lbrack \frac{V}{V_{0}} \right\rbrack^{2}P_{0} \\ & P_{c} = \left\lbrack \frac{200}{220} \right\rbrack^{2} \times 400 \\ & P_{c} = 331\text{ }W \end{matrix}$$