Alternating Current

An alternating voltage varies sinusoidally

An alternating voltage varies sinusoidally with time as v = v_m sin ωt. The current driven by it also varies with time and reverses direction periodic

The rms current and voltage

The rms current and voltage are the effective values used for power calculations. I = i_m/√2 = 0.707 i_m and V = v_m/√2 = 0.707 v_m. A 220 V household

For a pure resistor

For a pure resistor, current is in phase with voltage. The current is i = i_m sin ωt, with i_m = v_m/R. The average power is P = I^2R = VI.

In a pure inductor

In a pure inductor, current lags voltage by π/2. The current is i = i_m sin(ωt − π/2), and i_m = v_m/X_L where X_L = ωL. Inductive reactance increases

In a pure capacitor

In a pure capacitor, current leads voltage by π/2. The current is i = i_m sin(ωt + π/2), and i_m = v_m/X_C where X_C = 1/ωC. Capacitive reactance decr