. Motion picture electricity. l your attention toFig. 12, which represents a cop-per coil surrounding a soft ironcore. This core is under the in-fluence of a rotating magnet withone north and one south core is revolved by a belt orother means at high speed. Sup-pose the magnet poles N and Sare revolved at a speed of 3,600revolutions per minute, there be-ing two poles, one north and onesouth. Then the number of al-ternations during one minute will be equal to 3,600 multi-plied by 2 or 7,200 alternations per minute, which wouldbe correct for the current delivered to the line. Suppose, i
. Motion picture electricity. l your attention toFig. 12, which represents a cop-per coil surrounding a soft ironcore. This core is under the in-fluence of a rotating magnet withone north and one south core is revolved by a belt orother means at high speed. Sup-pose the magnet poles N and Sare revolved at a speed of 3,600revolutions per minute, there be-ing two poles, one north and onesouth. Then the number of al-ternations during one minute will be equal to 3,600 multi-plied by 2 or 7,200 alternations per minute, which wouldbe correct for the current delivered to the line. Suppose, in Fig. 12, that instead of driving the magnetat a speed of 3,600 revolutions it be turned only 1,800revolutions per minute; then the number of alternationswould be 1,800 times 2 or 3,600 alternations per minute. Let us take 7,200 alternations per minute and reducethis to cycles; first divide 7,200 by 2, which would equal3,600; then divide this amount by 60 seconds, which gives60—representing the number of cycles per ALTERNATIONS To figure the number of alternations deliveredper minute by an electric generator, multiply thenumber of magnet poles on the generator by thespeed in revolutions per minute. MOTION PICTURE ELECTRICITY 43 CYCLES PER SECOND When the number of alternations per minute isknown, the cycles may be determined by dividing___ the number of alternations by 2, then dividing theamount obtained by 60. The alternating current generator is an electricmachine in which, by the magnetism from rotatingpole pieces, currents are induced in copper coils,surrounding soft iron cores influenced by the ro-tating magnet poles. An alternating current electric generator canbe made to deliver a certain number of cycles persecond with a given number of rotating magnetpoles at a fixed speed. If the speed is doubled, thenumber of cycles per second is also doubled. Thenumber of cycles may also be doubled by increas-ing the number of rotating poles to twice the num-ber, or the
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