In an AC circuit, the current and voltage are time-dependent, making the instantaneous power also time-dependent. The average power of an alternating current circuit is defined as the time average of the instantaneous power over one cycle, where T is the period of the oscillations. By substituting instantaneous voltage and current equations and using trigonometric relations, the average power associated with a circuit element can be determined, wherein the term cos ϕ is the power factor. In the case of a resistor, the voltage and current are in phase; by substituting the root mean square value of current and voltage, the average power dissipated by a resistor can be determined. In the case of a capacitor and an inductor, the power factor turns zero. Thus, the average power dissipated by either of these elements is zero. In an RLC circuit, an AC source produces and absorbs power depending on its phase angle. By recalling the phase angle from the phasor diagram and substituting the root mean square values, the average power of an AC source can be determined.