. Practical electricity in medicine and surgery. in circuitwith a galvanometer whose resistance, together with that of theconnecting wires, is one ohm. Since the resistance of thecell itself is four ohms, approximately, the current will be * = i of the unit of current. Instead of speaking of units of current, etc., let us call the unit resistance one ohm, the unit cur-rent one ampere, and the unit electro-motive force one volt. Thenthe above current will be | ampere. Suppose, now, we had fiftycells of this kind joined in series, the current in this case wouldbe - -AO ; that is, 50 volts divide
. Practical electricity in medicine and surgery. in circuitwith a galvanometer whose resistance, together with that of theconnecting wires, is one ohm. Since the resistance of thecell itself is four ohms, approximately, the current will be * = i of the unit of current. Instead of speaking of units of current, etc., let us call the unit resistance one ohm, the unit cur-rent one ampere, and the unit electro-motive force one volt. Thenthe above current will be | ampere. Suppose, now, we had fiftycells of this kind joined in series, the current in this case wouldbe - -AO ; that is, 50 volts divided bv 200 ohms (= 50 X 2 0 0+1 • V X 4 + 1), equal to ^ of an ampere, nearly; hence the galva-nometer deflection would not be very different in the two cases, although we have increased theelectro-motive force fifty reason is that, notwith-standing the large increase inelectro-motive force, we haveincreased the total resistance ofthe circuit nearly in the sameproportion, since the cells makeup almost the entire KlG. ?J. A. Barrett Company JllL-AM-METER. But, suppose the galva-nometer had a resistance of 10,000 ohms, then one cell wouldgive a current of only Tq^o¥ ampere, while fifty cells wouldgive a current of x^VtaJ tnat is> almost fifty times as great. Inthis case the current would be increased approximately in pro-portion to the number of cells, for now the cells compose asmall part of the total resistance. Galvanometers which are direct-reading are generally called ampere, or mill-ampere, meters, or more simply ammeters,the name being taken from the practical unit of current calledthe ampere. (See page 119.) Potential Galvanometers, or Voltmeters.—Galvanometers areused not only to measure currents, but are also employed to POTENTIAL GALVANOMETERS, OR VOLTMETERS. 75 measure differences of potential. The principal of constructionis, however, the same, since the difference of potential is indi-cated by the current passing through t
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectelectri, bookyear1890
