Electrical measurementsA laboratory manual . w Fig. 35. send a current /^ through the unknown high resistance xand the galvanometer Gr (Fig. 35). The galvanometermust be one of the highest sensibility. Next let between L and T (Fig. 36) be employed to send acurrent through the known resistance r, and the galva-nometer shunted with resistance s; r must be largewith respect to q. Let the current through the galva-nometer be Ii. Then, L_ q x + g s + .g RESISTANCE. 85 Whence, x+g = ^ .P(r + ^ii^, M/WWWVt. Fig. 36. If S(^ may be neglected in comparison with r, and g s +9in comparison with a
Electrical measurementsA laboratory manual . w Fig. 35. send a current /^ through the unknown high resistance xand the galvanometer Gr (Fig. 35). The galvanometermust be one of the highest sensibility. Next let between L and T (Fig. 36) be employed to send acurrent through the known resistance r, and the galva-nometer shunted with resistance s; r must be largewith respect to q. Let the current through the galva-nometer be Ii. Then, L_ q x + g s + .g RESISTANCE. 85 Whence, x+g = ^ .P(r + ^ii^, M/WWWVt. Fig. 36. If S(^ may be neglected in comparison with r, and g s +9in comparison with a;, then 07= -^ . ^ .rIi q s or, if Ji and I2 are proportional to the deflections of thegalvanometer in the two cases, di q s Example. r = 250,000 ohms ; p = 10,200 ohms ; rfi = ; s = I; ^ = 200 ohms ; d2 = 10,200 X . X 250,000 X 10200 X X 106 ohms= megohms. 86 ELECTRICAL ME A S UEEMENTS. 49. Insulation Resistance by Direct Deflection.—When the constancy of the battery cannot be relied on,it may be found advantageous to proceed as follows:First find the figure of merit of the galvanometer (), ^ the current which will produce a deflectionof one division of the scale. The galvanometer thenbecomes an ammeter, and may be used in connection
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