- The rate at which a current supplies power to a device is
given by
Power = (current)*(voltage) Watts

- A device which runs for time
**t**at power level**P**uses up a total energyEnergy = P*t Joules

- For everyday appliances, a convenient unit for calculating energy
usage is the
**kilowatt-hour**:1 kWh = (1 kilowatt) * (1 hour) = 3,600,000 Joules

- Sending power over long distances can cause large ohmic losses
as the current heats up the wire. It helps to reduce the
size of the current, perhaps by boosting the voltage.
Devices called
**transformers**can do this, if they are given alternating current. -
**Alternating current**changes the direction of its voltage and current periodically. - In order to calculate the average resistance or average power
in an AC circuit, one must use the root-mean-square values
of voltage and current:
V(rms) = V(peak) / sqrt(2) = 0.707 V(peak) I(rms) = I(peak) / sqrt(2) = 0.707 I(peak)

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Copyright © Michael Richmond. This work is licensed under a Creative Commons License.