The conductors were built up of flat thin strips of copper for
flexibility. When the strips were allowed to lie closely together, the
short conductor showed an enormous self-induction, which cut down the
effective potential at its ends near the work. By spreading apart the
strips so as to lengthen a line around the conductor, the
self-induction could be easily made less than 35 per cent. of what it
had been before. The interweaving of the outgoing and return conductor
strands as one compound conductor gets rid almost entirely of the
self-inductive effects, because neither conductor has any free space
in which to develop strong magnetic forces, but is opposed in effect
everywhere by the opposite current in its neighbor.
Where a number of conductors are parallel, and have the same direction
of current, as in a coil or in a strand, it is evident that statically
the conductor may be considered as replaceable by a single conductor
with the same external dimensions and same total current in the area
occupied, the magnetic forces or lines surrounding them being of same
intensity. But with changing current strength the distribution of
current in the conductor has also a powerful effect on the energy
absorbed or given out in accordance with the magnetism produced. Hence
the self-induction of a strand, coil or conductor of the same section
varies with the rapidity of current changes, owing to the conduction
being uneven.
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