Question

An electric bulb rated as $500W-100V$ is used in a circuit having $200V$ supply. The resistance $R$ that must be put in series with the bulb, so that the bulb draws $500W$ is

• A. $100\Omega$
• B. $50\Omega$
• C. $20\Omega$
• D. $10\Omega$

Answer 1

The correct option is C $20\Omega$

We know that $P=Vi$
$\therefore$ Current through the circuit
$i=\frac{500}{100}=5A$
Potential difference across, $R=100V$
$\therefore$ relation $V=IR$
$100=5\times R$
$\Rightarrow R=\frac{100}{5}=20\Omega$