Text: Induction, Electromagnetic The production or inducing of electric currents in a conductor when it is moved in a magnetic field of force in such manner as to cut magnetic lines of force. The simplest example of this phenomena is the Faraday experiment in which he discovered that a wire with its ends joined, when moved rapidly in the field of a magnet, would result in current being induced in the wire or conductor. All dynamo electric machinery is based upon this principle of electromagnetic induction, as are also alternating current transformers and various other electrical devices. In the illustration is shown the theory of production of current by electromagnetic induction. Fig. 1 shows a coil of wire placed in a uniform magnetic field of force between two magnets. Here the coil is assumed to have been moved from A to B in the same plane. This is known as a motion of translation, and the field being uniform at all points the same number of lines pass through the coil at both points Therefore no current is induced in the coil and a sensitive instrument placed across the leads, C, C, would show no current present. In Fig. 2 the same coil is shown at A in its original position. Here, however, it is rotated, and when in position B it is apparent that less lines of force pass through it. We have thus fulfilled the conditions for inducing current, and if the instrument is placed across the leads, C, C, the presence of electric current will be indicated. If the motion of rotation is continued the number of lines of force passing through the coil will continue to increase and decrease and current will be produced in the coil as long as the motion persists. From the above it will appear that current can be induced either by rotating the coil around any axis in its plane, or by tilting it in its motion across the field. The coil of wire in this case is known as an inductor because the current is induced in it. It is also referred to as a conductor when describing the production of alternating currents. Now it was stated that current is induced in the inductor whether the lines of force through it are increased or decreased by its motion through the field. We can reduce the action to two simple rules. First, the relative motion between an inductor and a magnetic field must be such that the number of lines passing through the inductor are altered, i.e., increased or decreased. Second, the electromotive force induced in the inductor circuit will be proportional to the rate of increase or decrease in the number of magnetic lines embraced by the inductor circuit. We know from the Lenz Law (see Alternating Current, Theory of Production of ) that current will flow in the inductor in a direction dependent upon whether the lines of force through it are being increased or decreased, and as the inductor is being rotated continuously the current will change direction with each change in the number of lines. (See Alternating Current, Alternator, Electromotive Force, Fleming's Rule, Laws of Electromagnetic Induction, Lenz's Law.)

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