Question

When three identical bulbs of $60watt$, $200volt$ rating are connected in series to a $200volt$ supply, the power drawn by them will be :

• A. $180watt$
• B. $10watt$
• C. $20watt$
• D. $60watt$

Answer 1

Answer: (C)

$20watt$

If rated voltage = supply voltage then in series combination of bulbs
$\frac{1}{P_{eq}}=\frac{1}{P_1}+\frac{1}{P_2}+\frac{1}{P_3}+....$
For this question
$\frac{1}{P_{eq}}$ = $\frac{1}{60}$ + $\frac{1}{60}$ + $\frac{1}{60}$ $\Rightarrow P_{eq}=20watt$