Chapter-7|Alternating Current |NCERT 12th Physics:
Wattless Current:
The current which consumes no power for its maintenance in the circuit is called wattless current of idle current. Or
The current in AC circuit is said to be wattless if the average power consumed in the circuit is zero.
The average power of a given circuit is given by
The current Irms can be resolved into two components.
(I) Component Irms CosØ along Vrms, As the phase angle between Irms CosØ and Vrms is zero.
Therefore, Pav= Vrms×Irms×CosØ×Cos0
= Vrms×Irms×CosØ
(II) Component Irms SinØ is normal to Vrms, As the phase angle between Irms Sin Ø and Vrms is π/2.
Therefore,
Pav= Vrms×Irms×SinØ(Cosπ/2)=0
The component Irms SinØ is called Idle or wattless current because it does not consume any power in AC. This happens in the pure inductive or capacitive circuit in which the voltage and current differ by a phase angle of π/2.