First slide

Electrical power

Question

Three 60 W, 120 V light bulbs are connected across a 120 V power source. If resistance of each bulb does not change with current, then find out total power delivered to the three bulbs.

Moderate

A

180 W
B

20 W
C

40 W
D

60 W

Solution

Here $R = \frac{V^{2}}{P},$
Total power supplied
$= \frac{V^{2}}{3 / 2 R} = (\frac{2}{3}) (\frac{V^{2}}{R}) = \frac{2}{3} \times 60 = 40 W$

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