Chapter 24, Problem 1CQ

Why is the current in an ac circuit not always in phase with its voltage?

To determine

The reason for the current in an ac circuit is not in phase with its voltage.

Answer to Problem 1CQ

The current in an ac circuit is not in phase with its voltage because of the reactance of the passive elements of an ac circuit.

Explanation of Solution

The ac voltage is varied sinusoidal over time where as a dc voltage is not varied.

Since resistance is not dependent on frequency, current and voltage are in phase for a resistor. But in the passive elements like inductors and capacitors, the resistance is called as the reactance because it depends on the frequency.

This reactance tells about the relationship between the voltage and current in an ac circuit. In an inductor the current lags the voltage and in a capacitor the current leads the voltage.

When the capacitive reactance is greater than the inductive reactance in the LC circuit then the current leads the voltage. Similarly the inductive reactance is greater than the capacitive reactance then the current lags the voltage.

So the current lead or lag the voltage in the ac circuit.

Conclusion:

Therefore, the current in an ac circuit is not in phase with its voltage because of the reactance of the passive elements of an ac circuit.