. Dental and oral radiography : a textbook for students and practitioners of dentistry . toits influence is known as its magnetic field. The presenceof this magnetic field is easily demonstrated by placing amagnet under a sheet of paper upon which iron filingshave been evenly spread. By tapping the paper lightly,the filings will form into a series of curved lines extend-ing from one pole of the magnet to the other pole, as il-lustrated in Fig. 5. The formation of these definite HIGH TENSION ELECTRIC CURRENTS 37 curves indicates that the magnetic field exerts its influ-ence in certain definite
. Dental and oral radiography : a textbook for students and practitioners of dentistry . toits influence is known as its magnetic field. The presenceof this magnetic field is easily demonstrated by placing amagnet under a sheet of paper upon which iron filingshave been evenly spread. By tapping the paper lightly,the filings will form into a series of curved lines extend-ing from one pole of the magnet to the other pole, as il-lustrated in Fig. 5. The formation of these definite HIGH TENSION ELECTRIC CURRENTS 37 curves indicates that the magnetic field exerts its influ-ence in certain definite directions which are called thelines of magnetic force. These lines of force start at onepole of the magnet, pass in curved lines around to theopposite pole, where they re-enter and pass on throughthe magnet again, so that if any line is followed throughits entire length, one will eventually come back to thestarting point, as shown in Fig. 6. It is by virtue of its magnetic field, that a magnet hasthe power of attracting pieces of iron. When a piece of -v \ \ \ \ N\ \ M \ \ l J II /. ///hi11 \ \ ^ ~— ^y / i i i Fig. 6.—Diagrammatic illustration of the magnetic lines of force. iron is brought under its influence, it becomes a tem-porary magnet, and for the time being has its two the north pole of a magnet is brought close to a pieceof iron, a south pole will be induced in the iron next tothis north pole, and a north pole in the portion farthestfrom it. The attraction is then exactly similar to the at-traction between two permanent magnets when two un-like poles are brought together. This action of a mag-net in developing magnetism in iron placed in itsmagnetic field is called magnetic induction. When a piece of iron is in contact with a magnet, theattraction is greatest; but actual contact is unnecessary 38 DENTAL AND ORAL RADIOGRAPHY to magnetize the iron, as it need only be placed withinthe magnetic field, or, in other words, within the mag-netic lines of force of
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