Question

What is meant by the wattless current?

Hint:

In AC circuits, a wattless current occurs when the voltage and current are 90 degrees out of phase. This results in zero real power consumption, which happens in purely reactive circuits with only inductance or capacitance.

Answer 1

A wattless current refers to an alternating current (AC) that does not result in the transfer of real power to the load. This phenomenon occurs in an AC circuit when the current and voltage are out of phase by 90 degrees. The power consumed in such a circuit is zero because the energy supplied by the source is returned to the source in each cycle. This situation typically happens in circuits that are purely reactive (either capacitive or inductive), where the impedance is entirely due to inductance or capacitance.
When the voltage and current are 90 degrees out of phase, the power factor is zero, and no real power is delivered to the load. The formula for the power in an AC circuit is given by:
\[ P = V_{\text{rms}} I_{\text{rms}} \cos \phi \] Where \(P\) is the power, \(V_{\text{rms}}\) and \(I_{\text{rms}}\) are the root mean square values of voltage and current, and \(\phi\) is the phase difference between the voltage and current. When \(\phi = 90^\circ\), \(\cos 90^\circ = 0\), which results in zero power (wattless current).
This happens when the circuit consists purely of reactive elements (like inductors and capacitors), where the voltage and current are constantly changing direction and energy alternates back and forth between the source and the reactive components.