Bredhurst Receiving and Transmitting Society

3. Technical Basics

3e Inductors

3e.1 Recall that an inductor is normally a coil formed of a number of turns of wire.

Whilst a "conductor" is any piece of material that allows electrons to flow, such as a piece of wire, an "INDUCTOR" is normally a coil of a number of turns of wire. The wire is usually of large enough diameter so that it remains in the forms of the coil without collapsing if gently squeezed and is often in enamelled copper wire so that it is insulated from other components.

However the important point to note these words

"an inductor is normally a coil".

This indicates that and inductor does not have to be a coil of wire in fact any piece of wire, even one that is perfectly straight (as could be a straight piece of track on a PCB), can be an inductor and thus exhibit inductance. See below in section 3e.3 for more information on inductance.

3e.2 Recall that a current passing through a wire forms a magnetic field around the wire.

When a current passes through a wire it creates a magnetic filed around the wire. You cannot see it but you can detect it by using a small magnetic compass. By bringing the compass near to the wire the compass needle will swing and align in sympathy with the lines of magnetic force. As the compass is moved from one end of the wire to the other the way the needle points will change, following the lines of magnetic force.

As soon as the current is stopped the magnetic field collapses - almost at once. The larger the electric current the greater the magnetic filed.

In fact it was John Fleming (1849 - 1945) considered by many to be the "Father of Modern Electronics" who determined this effect of magnetism and electricity. From this Fleming's Left Hand rule came about which enables you to determine in which direction the magnetic force will be N - S, relative direction of current flowing (positive to negative) and if the wire is in a strong magnetic field movements of the wire.

First finger - direction of magnetic field (N-S) SeCond finger - direction of current (positive to negative) ThuMb - movements of the wire

3e.3 Recall that an inductor is able to store energy in its magnetic field.

Recall that the ability to store energy is known as inductance, which depends upon the number of turns of wire on the coil and its dimensions.

The inductor can store energy in the magnetic field caused by and electric current passing through it and this ability is called INDUCTANCE. The storage is not as prolonged as that as a battery and it is not the storage of an electrical charge but of energy.

The greater the number of turns the greater the inductance

Let's first look at that straight piece of wire mentioned in 3e.1 above. The ability to store energy is dependent upon the number of turns so a piece of wire with no turns would no have the ability to store much energy at all.

So as the number of turns of wire in the coil increases so does it ability to store energy increase and hence the amount of inductance increases.

The greater the size of turns in the coil the greater the inductance

Further as the size of the coil's dimensions increase of the coil itself so does it ability to store energy also increases and hence the amount of inductance increases.

The closer together turns of the coil the greater the inductance

But there is also a third factor to consider. In addition to the greater the number of turns and the greater the size of the coil, the closer together the turns as to each other the greater is the inductance.

Circuit diagrams of the inductor

It is necessary to know for the Intermediate Licence Examination that inductors have 3 different circuit diagram symbols.

	Standard (general) inductor.
	Inductor with iron core.
	a Transformer (two or more inductors with an iron core).