## Electronics Reference

# AC Circuits

The opposition of a circuit to the flow of a sinusoidal current is called impedance. It is the ratio of the phasor voltage (V) to the phasor current (I), measured in ohms (Ω). The impedance of a resistor, inductor, and capacitor can be determined using the equations above. Admittance (Y) is the inverse of impedance which is measured in siemens (S).

The impedance of a circuit can be expressed in rectangular form **Z**** =R+jX** where

**is the resistance and**

*R***is the reactance. It can be also expressed in polar form**

*X***Z=|Z|∠θ**.

The total or equivalent impedance of series impedances is the sum of the individual impedances.

The total or equivalent impedance of parallel impedances is determined by inverting the sum of the inverses of all impedances.