The power supplied to or dissipated by a resistor isP = I ^{2}Rjust as for DC circuits.

No power is dissipated by a capacitor or an inductor. That is, no power is dissipated by a pure inductor; if the inductor

alsohas resistance, its resistance dissipates power.Only the resistor dissipates energy or power.From the phasor diagram here, we can see that the resistance R is related to the total impedance Z by

R = Z cos so we can write the power as

P = I ^{2}Z cosor

P = I V cos This term cos is known as the

power factorof the circuit. For a circuit with only a capacitor or only an inductor the current and voltage are out of phase by ± 90° so the power factor is zero. This is another way of understanding that capacitors and inductors do not dissipate power. Remember, I or V without a subscript means the rms value of the current or voltage, I = I_{rms}and V = V_{rms}.In general, we can find the value of this phase angle or

power factorfrom(c) Doug Davis, 2002; all rights reserved

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