. Dental and oral radiography : a textbook for students and practitioners of dentistry . ect to its mag-netic field and becomes a magnet. the field due to the core, plus the field due to the currentpassing through the coil. Thus far we have discussed the fact that a magneticsubstance in the field of an ordinary magnet, or a con-ductor carrying an electric current, is magnetized. Thisphenomenon, we know, is due to magnetic induction. Itis also a fact that an electric current may he induced ina conductor by causing the latter to move through a mag-netic field. It makes no difference whether this
. Dental and oral radiography : a textbook for students and practitioners of dentistry . ect to its mag-netic field and becomes a magnet. the field due to the core, plus the field due to the currentpassing through the coil. Thus far we have discussed the fact that a magneticsubstance in the field of an ordinary magnet, or a con-ductor carrying an electric current, is magnetized. Thisphenomenon, we know, is due to magnetic induction. Itis also a fact that an electric current may he induced ina conductor by causing the latter to move through a mag-netic field. It makes no difference whether this fieldcomes from an ordinary magnet or from an electriccharge passing through a conductor. This action of a 40 DENTAL AND OIJAL RADIOGRAPHY magnet or of a current on a conductor moved in its fieldis called electromagnetic induction. Principles of Electromagnetic Induction If the ends of a coil of wire are connected with a gal-vanometer (Fig. 9) and the coil is moved down over anordinary magnet, the galvanometer will show that a mo-mentary electric current has passed through the B ■\ \v Fig. 9.—A, magnet with diagrammatic illustration of magnetic lines of force sur-rounding it. B shows a coil of wire connected to a galvanometer, C. The current continues as long as the coil is in motion,and ceases as soon as the coil is brought to rest. If thecoil is withdrawn from the magnet, a current is also in-duced which flows in an opposite direction to the currentwhich was induced when the coil was carried down overthe magnet. These induced currents are produced by the field sur-rounding the magnet moving or cutting across the wirescomposing the coil. If a current is passed through thecoil, it creates a magnetic field, and, on the other hand, HIGH TENSION ELECTRIC CURRENTS 41 the movement of a magnetic field within the coil producesa current. As a solenoid is surrounded by a magnetic field similarto an ordinary bar magnet, it follows that if a solenoidcarrying a current were thr
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