Question

$A\,220\,V,100\,W$ bulb is joined with a $110\, V$ supply. The power consumed by the bulb is

• A. 50 W
• B. 25 W
• C. 80 W
• D. 100 W

Answer 1

Answer: (B)

25 W

Answer 2

The electric power $P$ is given by $P=\frac{W}{t}=\frac{V^{2}}{R}$ watt where, $V$ is potential difference and $R$ the resistance. Given, $P_{1} =100 \,W , V_{1}=220\, V$ $\therefore R =\frac{V_{1}^{2}}{P_{1}}=\frac{(220)^{2}}{100}$ $=484 \,\Omega$ Hence, power dissipated when potential difference is $110 \,V$ is $P=\frac{(110)^{2}}{484}=25 \,W$