Capacitive Reactance

Author: E.E. Kimberly

With any applied voltage, the current that will flow into a perfect condenser in which there is no initial charge is proportional to its capacitance. The condenser is said to have capacitive reactance. The symbol for capacitive reactance is Xc. The effective current in a condenser with an impressed sinusoidal voltage is

[5-15]

where Ic = condenser current; Vc = effective voltage impressed on the condenser; Xc = capacitive reactance.

The current at any instant is

The maximum current is

Thus,

Since the current taken by a condenser is proportional to its capacitance and, by equation (5-15), it is inversely proportional to its reactance, then its reactance is inversely proportional to its capacitance. Hence,

By a procedure similar to that used in the case of inductive reactance, it may be shown that

Therefore,

(5-16)

(5-17)