AC1 Fundamentals Unit 7 – Capacitive Reactance
The total opposition to current flow in a circuit containing resistance (resistors) and capacitive
reactance (capacitors) is known as impedance (Z) and is measured in ohms.
You cannot directly add resistance (R) and capacitive reactance (XC) to obtain the impedance
value (Z).
In a series circuit with resistance and capacitive reactance, impedance (Z) is determined by the
following formula.
Z = √R^2 + XC^2
A more practical approach to finding the impedance (Z) of XC and R in series is to divide the
total circuit current (IT) into the applied voltage (Vac).
Vac
Z =
IT
In a parallel circuit with resistance and capacitive reactance, Z is determined by the following
formula.
RXC
Z =
√R^2 + XC^2
Again, a more practical approach to finding the impedance (Z) of XC and R in parallel is to
divide the total circuit current (IT) into the applied voltage (Vac).
Vac
Z = _____
IT