# Inductors

### Introduction

An inductor is a passive element designed to store energy in its magnetic field.
Inductors find numerous applications in electronic and power systems. They are used in power supplies, transformers, radios, TVs, radars, and electric motors.
Fig. 1: Typical form of an inductor
Any conductor of electric current has inductive properties and may be regarded as an inductor. But in order to enhance the inductive effect, a practical inductor is usually formed into a cylindrical coil with many turns of conducting wire, as shown in Fig. 1.
An inductor consists of a coil of conducting wire.
If current is allowed to pass through an inductor, it is found that the voltage across the inductor is directly proportional to the time rate of change of the current. Using the passive sign convention, $$v = L {di \over dt} \tag{1}$$ where L is the constant of proportionality called the inductance of the inductor. The unit of inductance is the henry (H), named in honor of the American inventor Joseph Henry (1797-1878). It is clear from Eq. (1) that 1 henry equals 1 volt-second per ampere.

### Symbols

The primary function of the inductor, however, is to introduce inductance-not resistance or capacitance-into the network. For this reason, the symbols employed for inductance are as shown in Fig. 2.
Fig. 2: Inductor symbols.
More details about inductor are given in the specific sections and topics of this chapter.