AC Theory

Alternating Voltages and Currents

Voltages and currents that vary with time, changing polarity and direction, commonly represented by sine waves.

Amplitude

The peak or maximum value of a sine wave, equal for both positive and negative half cycles.

Peak to Peak Value

The magnitude between the positive and negative peaks of a sine wave.

Periodic Time T

The time for one complete cycle of alternating current or voltage.

Frequency (f)

The number of cycles that occur every second, measured in Hertz (Hz).

Average Value of Sinusoidal AC

Zero over a complete cycle; for one half cycle, it equals approximately 0.637 times the maximum value.

Root Mean Squared (r.m.s) Value

The value of a sine wave that produces the same power as a constant direct current (DC) voltage or current.

Form Factor

The ratio of the r.m.s value to the average value of a sine wave, approximately equal to 1.11 for sine waves.

Phasor

A representation of alternating current or voltage with a fixed length for magnitude and an angle for phase.

Instantaneous Value

The value of a sinusoidal voltage or current at a specific moment in time.

Angular Frequency (ω)

The rate of rotation of the phasor, calculated as ω = 2πf.

Voltage Expression

For a sinusoidal voltage, v = Vmax sin(ωt) where Vmax is the maximum voltage.

Out of Phase

When two sine waves have a phase difference, such as 90° or π/2 radians.