Quote:
Originally Posted by 596
Power varies as the SQUARE of voltage. The ONE constant in this picture is the RESISTANCE of the bulb. SO, we first calculate that using the known starting spec of 60 watts at 240 volts. This gives us a bulb resistance of 960 ohms. Now, if we drop the voltage to 120 volts, the amps = 120 divided by 960, or 0.125 amps. The power can be calculated from I x E, which gives us 15 watts.
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Actually the power varies as the square of the
current, not the voltage (P=I^2R), but 15W is the correct answer.