Quotation from: General Science

Written by: Bertha M. Clark


311. The Practical Motor. A motor constructed in accordance with
Section 309 would be of little value in practical everyday affairs;
its armature rotates too slowly and with too little force. If a motor
is to be of real service, its armature must rotate with sufficient
strength to impart motion to the wheels of trolley cars and mills, to
drive electric fans, and to set into activity many other forms of
machinery.


The strength of a motor may be increased by replacing the singly
coiled armature by one closely wound on an iron core; in some
armatures there are thousands of turns of wire. The presence of soft
iron within the armature (Section 296) causes greater attraction
between the armature and the outside magnet, and hence greater force
of motion. The magnetic strength of the field magnet influences
greatly the speed of the armature; the stronger the field magnet the
greater the motion, so electricians make every effort to strengthen
their field magnets. The strongest known magnets are electromagnets,
which, as we have seen, are merely coils of wire wound on an iron
core. For this reason, the field magnet is usually an electromagnet.

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