ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
by the dashed arrows, does not link effectively because there is
only one layer of turns. A more inductive coil is shown in
figure 19, view B (on the previous page). The turns are closely
spaced and the wire has been wound in two layers. The two
layers link each other with a greater number of flux loops
during all flux movements, Note that nearly all the turns, such
as X, are next to four other turns (shaded). This causes the
flux .linkage to be increased.
A coil can be made still more inductive by winding it in three
layers, as shown in figure 19, view C. The increased number of
layers (crosssectional area) improves flux linkage even more.
Note that some turns, such as Y, lie directly next to six other
turns (shaded). In actual practice, layering can continue on
through many more layers. The important fact to remember,
however, is that the inductance of the coil increases with each
layer added.
As we have seen, several factors can affect the inductance of a
coil, and all of these factors are variable. Many differently
constructed coils can have the same inductance. The important
thing to remember, however, is that inductance is dependent upon
the degree of link axe between the wire conductor(s) and the
electromagnetic field. In a straight length of conductor there
is very little flux linkage between one part of the conductor
and another. Therefore, its inductance is extremely small. It
was shown that conductors become much more inductive when they
are wound into coils. This is true because there is maximum
flux linkage between the conductor turns, which lie side by side
in the coil.
d. Units of Inductance. As stated before, the basic unit of
inductance (L) is the HENRY (H), named after Joseph Henry, the
codiscoverer with Faraday of the principle of electromagnetic
induction. An inductor has an inductance of 1 Henry if an emf
of 1 volt is induced in the inductor when the current through
the inductor is changing at the rate of 1 ampere per second.
The Henry is a large unit of inductance, and is used with
relatively large inductors. With small inductors, the
millihenry is used. A millihenry is equal to 1 x 10 Henry, and
one Henry is equal to 1,000 millihenrys. For smaller inductors,
the unit of inductance is the microhenry. A microhenry is
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