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# When a light bulb is rated 100 w for 220 v supply. what is the resistance of the bulb and the peak voltage of the sources?

Updated: 10/31/2022

Wiki User

12y ago

Ohm's Law: Resistance is voltage divided by current

Power Law: Power is current times voltage

Combining them gives: Resistance is voltage squared divided by power

220 volts squared divided by 100 watts = 484 ohms. Note that this is hot resistance. If you measure the bulb in the cold state, you will get an entirely different, smaller, value, due to the extreme temperature coefficient of the filament.

Independently of that, since you ask for peak voltage, that means you are talking about an AC voltage source. We have to assume a sinusoidal waveform, and that the 220 volts was the RMS value. In this case, the peak value is simply the RMS value multiplied by the square root of 2, i.e. 0.707..., making the peak value 311 volts.

Wiki User

12y ago

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Q: When a light bulb is rated 100 w for 220 v supply. what is the resistance of the bulb and the peak voltage of the sources?