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Q.
A heater coil rated at $(1000\,W-200\,V)$ is connected to $110\, V$ line. What will be the power consumed?
J & K CETJ & K CET 2002
Solution:
From Joules law, the heat consumed is $P=\frac{V^{2}}{R}$
where $V$ is potential difference, $R$ the resistance.
$\therefore R=\frac{V^{2}}{P}$
Given, $V =200$ volt,
$P =1000\, W$
$\therefore R=\frac{(200)^{2}}{1000}=40 \Omega$
When using $100\, V$ line,
$P=\frac{V^{2}}{R} P=\frac{110 \times 110}{40}=302\, W$
$\therefore P \approx 300\, W$