An incandescent lightbulb rated at 100 W will dissipate 100 W as heat and light when connected across a 110-V ideal voltage source. If three of these bulbs are connected in series across the same source, determine the power each bulb will dissipate.

Find:
The power dissipated by a series of three light bulbs connected to the nominal voltage.
Assumptions:
The resistance of each bulb doesn’t vary when connected in series.


Analysis:

When connected in series, the voltage of the source will divide equally across the three bulbs. The voltage across each bulb will be 1/3 what it was when the bulbs were connected individually across the source. Power dissipated in a resistance is a function of the voltage squared, so the power dissipated in each bulb when connected in series will be 1/9 what it was when the bulbs were connected individually, or 11.11 W:



Connected in series and assuming the resistance of each bulb remains the same as when connected individually:

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