Question

An electric bulb is rated at $220\,V,$ $100\,W;$ Power consumed by it when operated at $110\,V$ is

• A. $25\,W$
• B. $50\,W$
• C. $75\,W$
• D. $90\,W$

Answer 1

Answer: (A)

$25\,W$

Answer 2

The electric bulb is rated $220\, V$ and $100 \,W$
$\therefore$ Resistance of the bulb
$R=\frac{V^{2}}{P}=\frac{(220)^{2}}{100}=484\, \Omega$
Power consumed when operated on $110\, V$ is
$P=\frac{V^{2}}{R}=\frac{(110)^{2}}{484}=25\, W$