Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . 53, or by thepoised solenoid, Fig. 148, inwhich the two terminals of themovable solenoid dip into twoconcentric circular grooves con-taining mercury in which con-tact is made. One groove is connected to each binding post by a wire,the groove stainped A, corresponding with post A, so that the directionof the current may be traced. When a current is sent through thecoil it takes up a position N and S just as in the case of the poisedneedle, and is also repelled orattracted by another m
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . 53, or by thepoised solenoid, Fig. 148, inwhich the two terminals of themovable solenoid dip into twoconcentric circular grooves con-taining mercury in which con-tact is made. One groove is connected to each binding post by a wire,the groove stainped A, corresponding with post A, so that the directionof the current may be traced. When a current is sent through thecoil it takes up a position N and S just as in the case of the poisedneedle, and is also repelled orattracted by another magnetor solenoid, the polarity beingas explained for a single con-volution, T[ 172. 176. Rules for Deter-mining Polarity of a Sole-noid.—Clasp the solenoid,or helix, in the right handso that the fingers pointaround it in the directionthat the current flows. Theoutstretched t h u m b, atright angles with the fin-gers, will point in the di-rection of the N-pole of thesolenoid, Fig. 149. To find the direction of current around the coil when thepolarity is known : clasp the coil with the right hand, so that. Fig. 148.—Ampere Frame Stand with movable coils are poised on needle pointsand the terminals dip in concentricmercury caps. ELECTRO MA GNETISM. 165 the thumb outstretched at right angles will point toward theN-pole, then the fingers will point in the direction of the cur-rent. If on viewing theend of a solenoid thecurrent flows aroundthat end, in the samedirection that thehands of a watchmove, Fig 150, thatend is S-polarity. Ifthe c u r r e n t flowsaround the coil againstthe direction in whichthe hands of a watch move, that end possesses N-polarity. 177. Graphical Field of a Solenoid.—The distributionof magnetism around a solenoid is very similar to that of abar magnet, and can be studiedby the iron filing diagram, DIRECTION OFMAGNETIC FORCE Fig. 149.
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