Impedance

From HvWiki

The impedance of a circuit is the total of all the effects that limit current flow in response to a voltage. It is generally frequency-dependant.

Impedance is defined as $Z = \frac{V}{I}$ in any electrical situation.

1 AC Circuits
- 1.1 Reactance
2 Other Kinds of Impedance
- 2.1 Characteristic Impedance

[edit]

AC Circuits

The impedance of a circuit to an AC voltage is found by combining the resistance of the circuit and the reactance, i.e. the response of elements like capacitors and inductors to changing voltage.

[edit]

Reactance

Reactance is analogous to resistance. A high reactance means that a large voltage is required for a current to flow.

Reactance comes in two forms, capacitive reactance (from capacitors) and inductive reactance (from inductors). Since these cancel out, they can be considered as positive or negative values on one reactance scale. The total reactance in a circuit is simply $X = X L - X C$

In the following, $ω$ is angular frequency. (See Frequency)

The formula for capacitive reactance is $X_C = \frac{1}{\omega C}$ . Thus the larger the capacitor and the higher the frequency, the lower the reactance.