Direct current (dc) refers to systems in which the source voltage is constant Alternating current (ac) refers to systems in which the source voltage varies periodically, particularly sinusoidally

An ac current is calculated using the peak current (determined by dividing the peak voltage by the resistance), the angular frequency, and the time For capacitors, we find that when a sinusoidal voltage is applied to a capacitor, the voltage follows the current by one-fourth of a cycle.

current — found by dividing the voltage by the resistance. sinusoidal voltage — applied to a capacitor, the voltage follows the current by one-fourth of a cycle. ac current — current that fluctuates sinusoidally with time at a fixed frequency. alternating current (ac) — flow of electric charge that periodically reverses direction.