The fundamental Ohm's law formulas for
a-c circuits are given by:

Where:

I = current in amperes,

Z = impedance in Ohms,

E = volts across,

Ø = phase angle in degrees.

The phase angle is defined as the difference

in degrees by which current leads voltage in a

capacitive circuit, or lags voltage in an inductive

circuit, and in series circuits is equal to the

angle whose tangent is given by the ratio X/R and

is expressed by:

arc tan (X/R)

X = the inductive or capacitive reactance in ohms,

R = the non-reactive resistance in ohms,

of the combined resistive and reactive components

of the circuit under consideration.

in a purely resistive circuit, Ø = 0°

in a purely reactive circuit, Ø = 90°

and in a resonant. circuit, Ø = 0°

Degrees x 0.0175 = radians.
1 radian = 57.3°

The power-factor of any a-c circuit is equal to
the true power in watts divided by the apparent
power in volt-amperes which is equal to the
cosine of the phase angle, and is expressed by

p.f. = the circuit load power factor,

E*I*cos Ø = the true power in watts,

E*I* = the apparent power in voltamperes,

E = the applied potential in volts

I = load current in amperes.

in a purely resistive circuit.

and in a reactive circuit,

and in a resonant circuit,

The fundamental Ohm's law formulas for

d-c circuits are given by,