Question

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

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

Answer 1

Answer: (C)

20 watt

Answer 2

If rated voltage = supply voltage then in a series combination of bulbs
$\frac{1}{P_{eq}}=\frac{1}{P_1}+\frac{1}{P_2}+\frac{1}{P_3}$+.......
For this question $\frac{1}{60}+\frac{1}{60}+\frac{1}{60}$ = $\frac{3}{60}$ = $\frac{1}{20}$ $\Rightarrow$ Peq = 20watt