That they oppose the magnetization is perfectly true,
but if you carefully laminate the iron so as to eliminate eddy
currents, you will find, strangely enough, that the magnetism rises
still more slowly to its final value. For by laminating the iron you
have virtually increased the self-inductive action, and increased the
time constant of the circuit, so that the currents rise more slowly
than before. The lag is not in the iron, but in the magnetizing
current, and the current being retarded, the magnetization is of
course retarded also.
CONNECTING COILS FOR QUICKEST ACTION.
Now let us apply these most important though rather intricate
considerations to the practical problems of the quick working of the
electromagnet. Take the case of an electromagnet forming some part of
the receiving apparatus of a telegraph system in which it is desired
to secure very rapid working. Suppose the two coils that are wound
upon the horseshoe core are connected together in series. The
coefficient of self-induction for these two is four times as great as
that of either separately; coefficients of self-induction being
proportional to the square of the number of turns of wire that
surround a given core.
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