What is meant by 'wattless current' in an AC circuit, and under what condition does it occur?

Answer and explanation

Correct answer: D. A current consuming zero average power when voltage and current are in quadrature (π/2 phase)

- The phase difference between voltage and current is ().
- The power factor is .
.
  1. Step 1: The average power in an AC circuit is , where is the power factor.
  2. Step 2: If the circuit contains only a pure inductor or a pure capacitor (with zero resistance ):
  3. Step 3: Consequently, the average power dissipated over a complete cycle is:
  4. Step 4: The component of alternating current that consumes no net power from the source is called wattless current ().
Answer
A current that consumes zero average electrical power, occurring when the phase angle between voltage and current is π/2 (purely reactive circuit)
Why not the others: 'Resistance infinite and voltage zero' means no current can flow at all; 'Produces zero magnetic field' contradicts Ampere's law (current in an inductor always creates a magnetic field); 'DC current flowing through a superconductor' is a persistent DC supercurrent, not an AC wattless current.

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