Q. The power of heater is 500 W at 800$℃$. What will be its power at 200$℃$ ? (Given : temperature coefficient of resistance, $\alpha = 4 \times 10^{- 4}℃^{- 1})$
A) 484 W
B) 672 W
C) 526 W
D) 620 W
Explanation
(d) $R_{200} = \frac{R_{800}}{1 + \alpha t}$
$\ R_{200} = \frac{R_{800}}{1 + 4 \times 10^{- 4} \times 600} = \frac{R_{800}}{1.24}$
$\ \frac{V^{2}}{R_{800}} = P\ $ ……(i)
and $\frac{\ \ \ \ \ \ V^{2}}{\ \ \ \ \ \ \ \ \ \ R_{200}} = P'$ ……(ii)
$\therefore\ \frac{P'}{P} = \frac{R_{800}}{R_{200}} = \frac{R_{800}}{\left( \frac{R_{800}}{1.24} \right)}$
${\ P}^{'} = 1.24P = 1.24 \times 500 = 620$ W
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.