# Resonance

Q value or figure of merit or Quality factor

In case of LCR circuit, the quality factor is defined as the ratio of voltage across inductor to the voltage across resistor.

i.e Q = XI /RI = wL/R

If R=0 then Q= ∞

Since inductances and capacitances are essentially energy-storing devices, it is convenient to determine the efficiency with which energy is stored and to compare alternative inductor or capacitor designs in terms of that efficiency. A figure of merit or Q value has been defined as:

**Expression for Impedance in a series**

The impedance Z of the series, LCR circuit is

**Expression modified for the small deviation from the resonant frequency**

A new variable δ may be defined as

This note is derived from MSC physics, Nepal.

This note is a part of the Physics Repository.

Next topic: Anti resonant circuit or Parallel Resonance