in ac currents when does wattless power occurs

Wattless power in AC circuits occurs when the current and voltage are out of phase by 90 degrees. This is typically the case in purely reactive loads, such as capacitors and inductors. Here's a step-by-step explanation:

1. In an AC circuit, the current (I) and voltage (V) typically oscillate sinusoidally and can be out of phase, meaning they don't reach their maximum and minimum values at the same time.

2. The power (P) in an AC circuit at any instant is given by P = VIcos(θ), where θ is the phase difference between the current and voltage. The term cos(θ) is known as the power factor.

3. When the current and voltage are in phase (θ = 0), cos(θ) = 1, and the power is maximized. This is known as active or real power and is what does useful work.

4. When the current and voltage are out of phase by 90 degrees (θ = 90°), cos(θ) = 0, and the power is zero. This is known as reactive or wattless power. It doesn't do any useful work, but it's necessary for the functioning of reactive components like inductors and capacitors.

5. In purely reactive loads, the current and voltage are always 90 degrees out of phase, so the power is always wattless. In practice, most loads are a combination of resistive and reactive elements, so there's usually some active power and some reactive power.