Question

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

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

Answer 1

Answer: (D)

The resistance of each bulb is $=\frac{V^2}{P}=\frac{(200{)}^2}{60}\Omega$
When three bulbs are connected in series their resultant resistance
$=\frac{3\times (200{)}^2}{60}$.
Thus power drawn by bulb when connected across $200V$ supply
$P=\frac{V^2}{R_{re}}=\frac{(200{)}^2}{3\times (200{)}^2/60}=20W.$