CP Workbook
Electric Power
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Recall that the rate at which energy is converted from one form to another is
power
.
power = energy converted / time
power = (voltage x charge) / time
power = voltage x (charge / time)
power = voltage x current
The unit of power is the
watt
(or kilowatt = 1000 watts).
So in terms of units,
electric power (watts) = current (amperes) x voltage (volts)
Thus,
1 watt = 1 joule / 1 second = 1 ampere x 1 volt
.
What is the power when a voltage of 120 V drives a 2-A current through a device?
What is the current when a 60-W lamp is connected to 120 V?
How much current does a 100-W lamp draw when connected to 120 V?
If part of an electric circuit dissipates energy at 6 W when it draws a current of 3 A, what voltage is impressed across it?
The 100 watt bulb draws more current and must therefore have a thicker filament.
The equation
power = energy
_{converted}
/ time
rearranged gives
energy
_{converted}
= power x time
Explain the difference between a kilowatt and a kilowatt-hour.
One deterrent to burglary is to leave your front porch light on all the time. If your fixture contains a 60-W bulb at 120 V, and your local power utility sells energy at 8 cents per kilowatt-hour, how much will it cost to leave the bulb on for the whole month?
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35A: Series and Parallel
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Textbook Set #6: Circuits with Multiple Batteries
Paul G. Hewitt
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