Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . s parallel to the lines of forceso that none thread through it,and the arrows indicate thedirection of the current. Therate of change is now a maxi-mum as is also the E. M. F. During the second quarter of the revolution the lines offorce thread through the opposite side, which is equivalent to-b,„ a further diminution of the lines of force through it, the rate ofchange and the E. M. F. decreas-ing until at half revolution theE. M. F. is zero. The direction ofthe E. M. F. is the sa
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . s parallel to the lines of forceso that none thread through it,and the arrows indicate thedirection of the current. Therate of change is now a maxi-mum as is also the E. M. F. During the second quarter of the revolution the lines offorce thread through the opposite side, which is equivalent to-b,„ a further diminution of the lines of force through it, the rate ofchange and the E. M. F. decreas-ing until at half revolution theE. M. F. is zero. The direction ofthe E. M. F. is the same through-out this half revolution, and thecurrent flows around the loopfrom a to c, to d, to b, to a,changing in strength with everyvariation of the generated E. M. the next half revolution thesame variations in E. M. F. occurbut the induced E. M. F. is in theopposite direction. The current is therefore reversed twice inevery revolution, or an alternating current flows around the loop. * The student is advised to read again If 291 which fully explains the fundamentalprinciple of the dynamo. 22. Fig. 306.—Direction and Magni tude of the Induced E. M. F. in a Dynamo. 338 PRACTICAL ELECTRICITY. 320. Alternating Current Dynamo.—To utilize the cur-rent flowing in the above closed loop when it is rotated in themagnetic field, some mechanical device must be used to leador collect the current from the rotating loop so that it willflow through a circuit external to it. Two collector rings areused for this purpose and consist of rings of copper mountedon a wooden or hard rubber hub, Fig. 307, this being mountedon the shaft with the loop. The rings are insulated from eachother and from the shaft. The terminals of the loop are con-nected, one to each ring, and stationary strips of copper, Pand M, termed brushes, rest upon the rings and are connected to the external the loop is re-volved a sliding orwiping contact is thusestablished and thecurrent is conducted
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