Question

A bulb rated 60W, 220V is connected across 110V mains line. The power consumed is

• A. 10W
• B. 15W
• C. 20W
• D. 25W

Answer 1

The correct option is B 15W

A $60$ Watt $220V$ bulb means that it will consume $60$ Watts when the voltage across it is $220V$.
In such a case the current flowing through it will be given by$I=W/V=60/220$ Amperes.
And the resistance of the filament will be $W/I^2=60\times (\frac{220}{60}{)}^2=806.67$ohms
Now when you just apply 110 volts across it instead of 220V. In this case the current flowing through the bulb will be given by,
$V/R=110/806.67=0.136$ Ampere
And the power would be$V\times I=110\times 0.136=14.96\approx 15$watts.