Question

Two $220$ volt, $100$ watt bulbs are connected first in series and then in parallel. Each time the combination is connected to a $220$ volt a.c. supply line. The power drawn by the combination in each case respectively will be :

• A. 50 watt, 100 watt
• B. 100 watt, 50 watt
• C. 200 watt, 150 watt
• D. 50 watt, 200 watt

Answer 1

Answer: (D)

$R =\frac{V^2}{P}= \frac{220\times 220}{100} = 484\, \Omega$
In series, $R_{eq} = 484 + 484 + 968\, \Omega$
$\therefore P_{eq} =\frac{V^2}{968}= \frac{220\times 220}{968} = 50$ watt
In parallel, $R_{eq} = 242\, \Omega$
$\therefore P_{eq} =\frac{V^2}{242}= \frac{220\times 220}{242} = 200$ watt.