Question

An electric bulb is rated $220\, V$ and $100\, W$ . What is the power consumed by it when operated on $110\, V$ ?

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

Answer 1

Answer: (A)

$25 \,W$

Answer 2

Resistance of the bulb $=\frac{V^{2}}{P}$
$=\frac{220\times220}{100}$
$=484 \, \Omega$
Power of the same bulb when operated on $110\,V$
$\frac{(V')^{2}}{R}$
$=\frac{110\times 110}{484}$
$=25\,W$