Question

The current which does not contribute to the power consumed in an AC circuit is called:

• A. Non-ideal current
• B. Wattless current
• C. Convectional current
• D. Inductance current

Answer 1

The correct option is B Wattless current

Wattless current does not contribute to the mean rate of working of the circuit.
As, power factor $=\frac{\text{true power}}{\text{apparent power}}$
$=cos\varphi$
$=\frac{R}{\sqrt{R^2+(X_L-X_C{)}^2}}$
$\therefore$ Power factor $=cos\varphi =\frac{R}{Z}$
In a non-inductive circuit, $X_L=X_C$
$\therefore$ Power factor $=cos\varphi =\frac{R}{\sqrt{R^2}}=\frac{R}{R}=1$
$\therefore \varphi =0^o$
This is the maximum value of power factor. Iris a pure inductor or an ideal capacitor
$\varphi ={90}^o$
$\therefore$ Power factor $=cos\varphi =cos{90}^o=0$.
Average power consumed in a pure inductor orb ideal capacitor
$P=E_V\cdot I_{V}cos{90}^o=zero$.
Therefore, current through pure L or pure C; which consumes no power for its maintenance in the circuit is called ideal current or wattless current.