. Laboratory exercises in elementary physics. Wire. R. L. Av. * As all that is needed is to get the same galvanometer-reading, itis not necessary to reverse the galvanometer. In this case, however,all deflections must be on the same side. The first and second read-ings should be taken in as rapid succession as possible, in order todecrease the effect of any possible change in the current. MEASUREMENT OF RESISTANCE. 45 EXERCISE 8, B. MEASUREMENT OF RESISTANCE. Preliminary.—When, in such an apparatus as Fig. 30 rep-resents, the current of the battery B comes to the point a,it divides, part going
. Laboratory exercises in elementary physics. Wire. R. L. Av. * As all that is needed is to get the same galvanometer-reading, itis not necessary to reverse the galvanometer. In this case, however,all deflections must be on the same side. The first and second read-ings should be taken in as rapid succession as possible, in order todecrease the effect of any possible change in the current. MEASUREMENT OF RESISTANCE. 45 EXERCISE 8, B. MEASUREMENT OF RESISTANCE. Preliminary.—When, in such an apparatus as Fig. 30 rep-resents, the current of the battery B comes to the point a,it divides, part going down the side abd and part down theside accl. If the resistances of the two sides are alike, thesame amount of current will flow through each; but if theyare not alike, more current will follow the side having theless resistance. If wTe attach wires at the points b and cand connect them with the galvanometer, so long as thesame amount of current passes on each side the galvanome-ter will not be affected; but if the resistance of one side. be made greater than that of the other, then the currentwill flow through the galvanometer from the side carryingthe greater current. Suppose we insert in cd a resistance-box, and in bd the body whose resistance we wish to meas-ure, x. If the resistance-box is at 0, the resistance of xwill hold back the current in bd, and a portion of it willflow from b to c through the galvanometer, which will bedeflected. Suppose now we increase the resistance in thebox until the galvanometer reads 0, then we know that theresistance of acd equals the resistance of abd (since thewires of which the instrument are constructed have practi- 46 CURRENT ELECTRICITY. cally no resistance), and that the required resistance of xequals the known resistance in the box. Wheatstones Bridge.—On a board is placed a square ofwire, abed, Fig. 31, with a binding-post at each corner. B
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
