Explanation
INDUCTIVE CIRCUIT
We know that in pure inductive circuit, current is lagging by 90 degree from voltage (in other words, Voltage is leading 90° from current) i.e the phase difference between current and voltage is 90 degrees.
As explained above, if current and voltage are 90° out of phase from each other like in pure inductive circuit, the total power of the circuit would be 0 as follow.
P= V I Cos θ
if angle between current and Voltage are 90° (θ = 90), then
Power P = V I Cos (90°) = 0
This shows that in case of pure inductive circuit, the total power of the circuit would have zero as Cos 90° = 0.
CAPACITIVE CIRCUIT
We know that in pure capacitive circuit, current is leading by 90° from voltage (in other words, Voltage is lagging 90° from current) i.e the phase difference between current and voltage is 90 degree.
As mentioned above, if current and voltage are 90° out of phase from each other like in pure capacitive circuit, the total power of the circuit would be zero as follow.
Power in AC Circuit
P= V I Cos θ
if angle between current and Voltage are 90 ( θ = 90) Degree. then
Power P = V I Cos (90°) = 0
This shows the same as like pure inductive circuit i.e. in case of pure capacitive circuit, the total power of the circuit would be zero as Cos 90° = 0.