4. The Inductor

In its most basic form, an Inductor is simply a coil of wire. For most coils the current, ( i ) flowing through the coil produces a magnetic flux, ( NΦ ) that is proportional to it. In Electromagnetism we have seen that when electrons flow through a conductor a magnetic flux is developed around the conductor producing a relationship between the direction of this flux and the direction of the electron flow called the "Left Hand Rule". But another important property of a wound coil is to use this magnetic flux to oppose or resist any changes in electrical current flowing through it.

The Inductor is another passive type electrical component designed to take advantage of this relationship by producing a much stronger magnetic field than one that would be produced by a simple coil. Inductors are formed with wire tightly wrapped around a solid central core which can be either a straight cylindrical rod or a continuous loop or ring to concentrate their magnetic flux. The schematic symbol for a inductor is that of a coil of wire so therefore, a coil of wire can also be called an Inductor. Inductors are categorised according to the type of inner core with the different core types being distinguished by adding continuous or dotted parallel lines next to the wire coil as shown below.

a. Inductor Symbols

The current, i that flows through an inductor produces a magnetic flux that is proportional to it. But unlike a Capacitor which opposes a change of voltage across their plates, an inductor opposes the rate of change of current flowing through it due to the build up of self-induced energy within its magnetic field. In other words, inductors resist or oppose changes of current but will pass a steady state DC current. This ability of an inductor to resist changes in current and which also relates current, i with its magnetic flux linkage, NΦ as a constant of proportionality is called Inductance which is given the symbol L with units of Henry, (H) after Joseph Henry.

Because the Henry is a relatively large unit of inductance in its own right, for the smaller inductors sub-units of the Henry are used to denote its value. For example:

Prefix	Symbol	Multiplier	Power of Ten
milli	m	1/1,000	10-3
micro	µ	1/1,000,000	10-6
nano	n	1/1,000,000,000	10-9

So to display the sub-units of the Henry we would use as an example:

• 1mH = 1 milli-Henry - which is equal to one thousandths (1/1000) of an Henry.
• 100uH = 100 micro-Henries - which is equal to 100 millionths (1/1,000,000) of a Henry.

Next topic will be on capacitors