Impedance

Definition

Impedance is the total opposition a circuit presents to the flow of alternating current (AC) at a given frequency. It combines resistance, inductive reactance, and capacitive reactance.

5 Must Know Facts For Your Next Test

1. Impedance is represented by the symbol $Z$ and measured in ohms ($\Omega$).
2. The formula for impedance in an RLC series circuit is $Z = \sqrt{R^2 + (X_L - X_C)^2}$, where $R$ is resistance, $X_L$ is inductive reactance, and $X_C$ is capacitive reactance.
3. Inductive reactance ($X_L$) increases with frequency, while capacitive reactance ($X_C$) decreases with frequency.
4. The phase angle ($\theta$) between the voltage and current in an AC circuit can be found using $\tan(\theta) = \frac{X_L - X_C}{R}$.
5. At resonance in an RLC series circuit, inductive reactance equals capacitive reactance ($X_L = X_C$), resulting in minimum impedance equal to the resistance ($Z = R$).

Review Questions

• What components contribute to impedance in an AC circuit?
• How do you calculate the total impedance in an RLC series circuit?
• What happens to impedance at resonance in a series RLC circuit?

Related terms

Resistance:

A measure of the opposition to direct current (DC), represented by $R$, and measured in ohms ($\Omega$).

Inductive Reactance:

The opposition an inductor presents to alternating current due to its inductance, given by $X_L = \omega L$, where $\omega = 2\pi f$ and L is inductance.

Capacitive Reactance:

The opposition a capacitor presents to alternating current due to its capacitance, given by $X_C = \frac{1}{\omega C}$, where $C$ is capacitance.