Quote:
Originally Posted by Speedy Petey
No Push.
60w@ 240v = 30w@120v
I over though it and confused myself over something extremely simple.
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Sorry to break in here, but this discussion has gone off the track! The above quoted statement is very very wrong.
The mistaken assumption in this discussion is that the POWER number 60 watts was a constant, or that power varied directly as volts. BOTH of these assumptions are
wrong.
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.