Capacity introduced into a circuit containing inductance reduces the latter and if enough be introduced, inductance will be neutralized, giving a resonant circuit which will act as though only resistance were present.
Fig. 1,336.—Impedance diagram for circuit containing resistance, inductance and capacity. The symbols correspond to those used in equation (1) below. In constructing the diagram from the given values, lay off AB = resistance; at B, draw a line at right angles, on which lay off above the resistance line, BC = inductive reactance, and below, BD = capacity reactance, then the resultant reactance = BC - BD = BD'. Join A and D', then AD' = impedance.
Ques. What is the expression for impedance of a circuit containing resistance, inductance and capacity?
Ans. It is equal to the square root of the sum of the resistance squared plus the square of inductance reactance minus capacity reactance.
This is expressed plainer in the form of an equation as follows:
impedance = √(resistance2 + (inductance reactance - capacity reactance)2)
or, using symbols,
Z = √(R2 + (Xi - Xc)2) (1)