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. Conventional current
D. Inductance current

Answer 1

Hint: If the average power consumed in a circuit is zero then the current in that circuit is said to be wattless current. It is also called idle current.
Average power is the product of voltage current and power factor. In equation form it can be represented as
$P = V \times I \times \cos \phi $
Where, $V$ is the voltage, $I$ is the current and $\cos \phi $ is the power factor.
When $\phi = {90^0}$ power becomes zero.
Since, $\cos \,{90^0} = 0$
For $\phi $ to become ${90^0}$ we need to use a pure inductor or ideal capacitor. The phase difference between voltage and current in a pure inductor or a pure capacitor circuit will be ${90^ \circ }$.
So, the average power in a pure inductor circuit or ideal capacitor will be zero.

Complete step by step answer:
If the average power consumed in a circuit is zero then the current in that circuit is said to be wattless current. It is also called ideal current.
Average power is the product of voltage current and power factor. In equation form it can be represented as
$P = V \times I \times \cos \phi $
Where, $V$ is the voltage,$I$ is the current and $\cos \phi $ is the power factor.
Power factor is the cosine of angle between voltage and current.
It is given by the equation.
${\text{power}}\,{\text{factor = }}\dfrac{{{\text{true}}\,{\text{power}}}}{{{\text{apparent}}\,{\text{power}}}}$
Power factor will become zero
When $\phi = {90^0}$
Since, $\cos \,{90^0} = 0$
For $\phi $ to become ${90^0}$ we need to use a pure inductor or ideal capacitor. The phase difference between voltage and current in a pure inductor or a pure capacitor circuit will be ${90^ \circ }$.
So, the average power in a pure inductor or ideal capacitor
$
  P = V \times I \times \cos \phi \\
   = V \times I \times 0 \\
   = 0 \\
 $
Thus, if we use a pure inductor or pure capacitor power consumed will be zero. Then the current in that circuit is called ideal or wattless current.
$\therefore$ The correct option is B.

Note: Wattless current is not possible in a circuit involving resistance. It is possible only in circuits where the voltage and current have a phase difference of ${90^ \circ }$ so that power factor becomes zero.
Average power is the product of voltage current and power factor. In equation form it can be represented as
$P = V \times I \times \cos \phi $
Where, $V$ is the voltage, $I$ is the current and $\cos \phi $ is the power factor.