POWER IN AC CIRCUITS

Power is dissipated in AC resistive circuits the same way as in DC resistive circuits. Power is measured in watts and is equal to the current times the voltage in the circuit.

The power consumed by the resistor in an AC circuit varies with the amount of current flowing through it and the voltage applied across it. 

The relationship of power, current, and voltage in resistive AC circuit.

Picture shows the relationship of power, current, and voltage. The power curve does not fall below the reference line because the power is dissipated in the form of heat. It does not matter in which direction the current is flowing, as power is assumed to have a positive value.

Power varies between the peak value and 0. Midway between peak value and 0 is the average power consumed by the circuit. In an AC circuit, the average power is the power consumed. This can be determined by multiplying the effective voltage value by the effective current value. This is expressed as

P=IE