Phase angle

Definition

Phase angle is the measure of the phase difference between the voltage and current in an AC circuit, usually expressed in degrees. It indicates whether the current leads or lags behind the voltage.

5 Must Know Facts For Your Next Test

1. The phase angle is calculated using $\phi = \arctan\left(\frac{X_L - X_C}{R}\right)$, where $X_L$ is inductive reactance, $X_C$ is capacitive reactance, and $R$ is resistance.
2. A positive phase angle means that the current lags behind the voltage (inductive circuit), while a negative phase angle means that the current leads the voltage (capacitive circuit).
3. In a purely resistive AC circuit, the phase angle is zero because voltage and current are in phase.
4. The magnitude of the impedance in an RLC series circuit can be found using $Z = \sqrt{R^2 + (X_L - X_C)^2}$.
5. When $X_L = X_C$, resonance occurs, and the phase angle becomes zero as voltage and current are perfectly in phase.

Review Questions

• What does a positive phase angle indicate about an AC circuit?
• How do you calculate the phase angle in an RLC series circuit?
• What happens to the phase angle at resonance?

Related terms

Impedance:

The total opposition to current flow in an AC circuit, combining resistance and reactance, measured in ohms ($\Omega$).

Resonance:

The condition in which inductive reactance equals capacitive reactance ($X_L = X_C$) resulting in a purely resistive impedance.

Reactance:

The opposition to alternating current by inductance or capacitance, measured in ohms ($\Omega$). Inductive reactance ($X_L$) and capacitive reactance ($X_C$) are its two types.