Free-Ed: Basic Electronics Fundamentals

AC Components and Circuits
Inductive Reactance

Section 2-4 The Q of an Inductor

Definition

Q of an Inductor

The Q of an inductor is the measure of its quality. The more 'perfect' the inductor, the higher its Q value.

Q is defined by this equation:

Where:

Q is the quality of the inductor (unitless)

X_L is the inductive reactance (Ohms)

r_i is the DC internal resistance of the inductor (Ohms)

The Q of a coil is also known as the merit of a coil.

A 'perfect' inductor would have no internal resistance and, therefore, a Q of infinity. Although it is possible to achieve Qs on the order of 2000 or so, most inductors have Q values that are less than 100 when used in their intended frequency ranges.