3. Technical Basics
3e Inductors
3e.1 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 field 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 field.
Recall that an inductor is normally a coil formed of
a number of turns of wire to concentrate the magnetic field.
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 which will concentrate the magnetic field 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 an 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.
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 not 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 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 are to each other the greater is the inductance.
|