RMS, Phase difference and Impedance

Mean and RMS values of AC

The mean value of alternating current over complete cycle is zero

While for half cycle it is

An instrument read root mean square values as

Phase difference between voltage and current

Area may be controlled by resistance, inductance and capacitance. Due to the presence of inductance and capacitance, current is usually not in phase with applied voltage. In general

 V =V0 sin ωt

 I =I0 sin (ωt +φ)

where φ is the phase difference.

Impedance and Reactance

The hindrance offered by a circuit to flow of AC is called impedance. It is denoted by Z.


Reactance : The hindrance offered by inductance and capacitance in ac circuit is called reactance. It is denoted by X.

The hindrance due to inductance alone is called the inductive reactance while that due to capacitance alone is called the capacitive reactance.

Inductive reactance,  X= ωL

Capacitive reactance,