Question

A heater coil rated at $(1000W-200V)$ is connected to $110V$ line. What will be the power consumed?

• A. 200 W
• B. 300 W
• C. 250 W
• D. 350 W

Answer 1

Answer: (B)

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,
$P=1000W$
$\therefore R=\frac{(200{)}^2}{1000}=40\Omega$
When using $100V$ line,
$P=\frac{V^2}{R}P=\frac{110\times 110}{40}=302W$
$\therefore P\approx 300W$