The outlines of physics: an elementary text-book . h ab will be the same asthat through ad, and there will be no difference of poten-tial between b and d. A galvanometer inserted betweenthese points will show no flow of current, however large acurrent may be flowing through the divided circuit. Ifthree of the four resistances above mentioned are known,the fourth one can be computed by means of the aboveproportion. This arrangement is called a Wheatstonehbridge. 265. Resistance Soxes. — For convenience in the^ com-parison of resistances, it is customary to place a setof coilsof wire, previously
The outlines of physics: an elementary text-book . h ab will be the same asthat through ad, and there will be no difference of poten-tial between b and d. A galvanometer inserted betweenthese points will show no flow of current, however large acurrent may be flowing through the divided circuit. Ifthree of the four resistances above mentioned are known,the fourth one can be computed by means of the aboveproportion. This arrangement is called a Wheatstonehbridge. 265. Resistance Soxes. — For convenience in the^ com-parison of resistances, it is customary to place a setof coilsof wire, previously adjusted to measure an exact numberof ohms each, within a box. The terminals of these coilsare attached to a row of brass blocks fastened to the topof the box as shown in Fig. 265, and these blocks may beconnected by the insertion of plugs. The general appear-ance of such a box is shown in Fig. 266. The values of MEASUREMENT OP CURRENT 29d the coils are like those of a set of weights, 1, 2, 2, 5,10, 20, 20, 60,100, 200, 200, 500, etc. ? T. Fig. 265. Fig. 266. 266. Experiment 83. — Measurement of the Resistance of a Coilof Copper Wire with the Wheatstones : (1) A piece of iron or German silver wire 1 m. long; a meter stick. (2) The resistance box used in the foregoing determination. (3) A coil or spool of fine copper wire, the resistance of which is tobe measured. (4) A galvanometer. .Procedure : (a) Stretch the piece of iron or German silver wire between twobinding screws, adjusting it so that the length is as nearly as possible1 m. Lay the meter stick alongside the wire with its ends corre-
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
