Question

an electric bulb markwd as 50 watt-220volt is connected across a 100 volt supply. what is the present power of the bulb?

Answer 1

It is impossible to give you an accurate answer. It would be tempting to simply use Ohm’s Law and declare that the incandescent light bulb had a resistance of 800 Ohms, so that when operated at 100 Volts, the new power level would be 12.5 Watts. (A quick mental rule is halving the voltage quarters the power.) But, this would be wrong.