How is power calculated in an AC circuit with reactance?

Power in an AC circuit with reactance is calculated using the formula P = VIcosφ.

In an AC circuit with reactance, the current and voltage are not in phase due to the presence of reactance. The power in the circuit is therefore not simply equal to the product of the current and voltage, as it is in a purely resistive circuit. Instead, the power is calculated using the formula P = VIcosφ, where V is the RMS voltage, I is the RMS current, and cosφ is the power factor.

The power factor is a measure of how much of the total power is being used to do useful work, and how much is being lost as heat in the circuit. In a purely resistive circuit, the power factor is equal to 1, as the current and voltage are in phase and all of the power is being used to do useful work. In a circuit with reactance, the power factor is less than 1, as some of the power is being lost due to the phase difference between the current and voltage.

To calculate the power factor, the phase angle between the current and voltage must be determined using a phase angle meter or an oscilloscope. The power factor can then be calculated as cosφ = P/(VI), where P is the power in watts, V is the RMS voltage in volts, and I is the RMS current in amps.