Electrical instruments and testing; how to use the voltmeter, ohmmeter, ammeter, potentiometer, galvanometer, the Wheatstone bridge, and standard portable testing sets (1907)
Schneider, Norman H. (Norman Hugh), Hargrave, Jesse · New York, Spon & Chamberlain; [etc., etc.] · leaf 140
istance of a Cell. Take open circuit e.m.f. of cell with voltmeter ofknown resistance R. Add resistance r in series with cell and volt-meter and adjust until e.m.f. deflection is one-half. Calculation: Add additional resistance to that ofvoltmeter so as to obtain total resistance in serieswith… … Fig. 77. Example. Voltmeter = 521 ohms, e.m.f. 1.5volts; adding 530 ohms reduces e.m.f. to .75 volt.Total resistance 521 + 530 = 1051. This less 521 x2 or 1042 = 9 ohms. Formula. (R + r) - 2 R = cell resistance. Second Method. In Fig. 77 C is the cell whoseinternal resistance it is desired to…
Electric testing · Electric apparatus and appliances
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