Question

When three identical bulbs of $60\, W, 200$ 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 $200\, V$ supply
$P=\frac{V^{2}}{R_{r e}}=\frac{(200)^{2}}{3 \times(200)^{2} / 60}=20\, W .$