ELECTEICAL MEASUBEMENTS 



321 



Method for the Direct Measurement of Absorption Resistance 

 In a Wheatstone bridge (Fig. 3) let the resistance of the different 



arms be denoted by R,, R', R tl , R" and r. Let J^have in circuit a 



self-inductance L t and let r have in circuit with it a self-inductance. 

 Let C, ibt be the current through R, and C ** + *) be the current 



through r when a periodic electromotive force is applied to a and d in 



the figure. 



Let C' be the current through R t , and C" be the current through r 



when there is a constant difference of potential between a and d. The 



ratio of the current in this case is 



c' 



R"R-R'R 



R (R" 



_ 

 r(R' + R"} 



FIG. 4. 



When a periodic electromotive force is applied to a and d, the ratio 

 of the currents in this case is 



__ 



C 1 ~ R (R >r +RJ + r (R~+~R') + ibl (R + R") 



Separating the real and imaginary parts 

 o ,_ (R"R 



If now the fixed coils of the electrodynamometer are placed in the 

 R, arm of the bridge, and the hanging coil is placed in cross connection 

 of the bridge, as in Fig. 4, the different resistances may be adjusted 

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