Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . d when bal-ance is obtained : the 10 ohm spool was selected, B = 350 scale divi-sions read from the left-hand zero mark, C = 650 divisions read fromright-hand zero mark. What is the value of the unknown resistanceat D, Fig. 229 ? By Formula (91) D = A * C =-10 * 650 = ohms.±> 3o0 A = 10 ohms, C = 650 divisions, B = 350 107: In another measurement with the slide wire bridge, A= 100 ohms, B = 100 divisions, C = 900 divisions. What is the valueof the unknown res
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . d when bal-ance is obtained : the 10 ohm spool was selected, B = 350 scale divi-sions read from the left-hand zero mark, C = 650 divisions read fromright-hand zero mark. What is the value of the unknown resistanceat D, Fig. 229 ? By Formula (91) D = A * C =-10 * 650 = ohms.±> 3o0 A = 10 ohms, C = 650 divisions, B = 350 107: In another measurement with the slide wire bridge, A= 100 ohms, B = 100 divisions, C = 900 divisions. What is the valueof the unknown resistance ? By Formula (91) D = ^-^ = 100*09Q0 = 900 ohms. Prob. 108 : What is the value of an unknown resistance measuredby the slide wire bridge when A = 1 ohm, B = 900 divisions, C =100 divisions. By Formula (91) D = A * C = 1 ^0^°° = .11 ohm. Problems 107 and 108 illustrate about the range of the bridge withthe spools furnished, but the per cent of error in measurement in-creases as the resistance to be measured increases, and measurementsare more accurate for low resistances with this type of bridge,. MEASUREMENT OF RESISTANCE. 257 250. Students Wheatstone Bridge {Lozenge Pattern).—The Wheatstone bridge is based upon the same principle ofbalancing potentials in a divided circuit as explained in ^f 248. In Fig. 230 a simple diagram of the circuit is given. A,B, C, and D are called the arms of the bridge. The unknownresistance is connected at D, a variable rheostat at C, and re-sistance spools are inserted in the arms, A and B. The con-nections and apparatus required for making measurements bythe students lozenge bridge are illustrated in Fig. 232. Oneof the spools of the resistance set, which was previously cal-culated by Formula (22) is inserted in the D arm for verifica-tion of the calculation by electrical measurement. The ap-paratus illustrated comprises the following parts : lozengebridge with spools, students Daniell cell, adjustable graduatedrheostat, double conta
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