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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1884 Excerpt: ...generator; for in these generators the intensity of the magnetic-field is not constant, but directly depends on the rate of rotation of the armature whilst the processes in the interior of the generator are rather more complicated. As regards a dynamo, therefore, we shall still have to answer three important questions. VI. What is the ratio between current and rate of rotation in dynamo-electric generators? VII. What relation has the effective magnetism in dynamo-electric generators to the rate of rotation of the armature, and to the increase of current? VIII. How many turns of wire must be wound on the field-magnets, and on the armature, in dynamo-electric generators, in order to obtain the maximum efficiency? The answers to questions VI and VII are given in an extremely interesting article by Dr. 0. Frohlich, in the "Monatshefte" of the Berlin Academy of Science, published 30th November, 1880. This article explains a theory based on a large number of experiments, and is of great value. We shall now discuss the most important points of this theory. According to Ohm's law, /-A R in which equation, as previously, / represents the quantity of current,.# the electromotive force, R the resistance. The electromotive force, however, as already mentioned, is proportionate to the number of windings (n) on the armature, and its rate of rotation (v and to the intensity of the magnetic field; or, as Dr. Frohlich expresses it, to the "effective magnetism (M )." Ohm's Jaw can, therefore, be written thus: In magneto-electric generators, with steel magnets, the effective magnetism is constant, and depends only on the strength of the magnets. In magneto-electric generators with electro-magnets, it depends on the current traversing the coils of the magne...
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