Impedance

Definition

Impedance is the measure of opposition that a circuit presents to the flow of alternating current (AC) at a particular frequency. It combines resistance, inductive reactance, and capacitive reactance into a single value represented as a complex number.

5 Must Know Facts For Your Next Test

1. Impedance ($Z$) is measured in ohms ($\Omega$).
2. It is calculated using $Z = \sqrt{R^2 + (X_L - X_C)^2}$, where $R$ is resistance, $X_L$ is inductive reactance, and $X_C$ is capacitive reactance.
3. The phase angle ($\theta$) between voltage and current in an AC circuit can be determined using $\tan(\theta) = \frac{X_L - X_C}{R}$.
4. Impedance affects both the amplitude and phase of the voltage and current in an AC circuit.
5. In purely resistive circuits, impedance equals resistance ($Z = R$), while in purely reactive circuits (inductive or capacitive), it equals reactance.

Review Questions

• How do you calculate impedance in an RLC series circuit?
• What role does impedance play in determining the phase angle between voltage and current?
• Why is impedance represented as a complex number?

Related terms

Resistance:

Resistance ($R$) opposes the flow of electric current through a conductor. It is measured in ohms ($\Omega$).

Inductive Reactance:

Inductive reactance ($X_L$) represents the opposition to the change in current by an inductor. It is calculated as $X_L = \omega L$, where $\omega$ is angular frequency and $L$ is inductance.

Capacitive Reactance:

Capacitive reactance ($X_C$) represents the opposition to the change in voltage by a capacitor. It is given by $X_C = \frac{1}{\omega C}$, where $\omega$ is angular frequency and $C$ is capacitance.