Electrical measurementsA laboratory manual . h their steadyvalues between consecutive reversals. The equation may be demonstrated as follows: Letii be the current through AC and 2*3 that through AD(Fig. 119), at the same instant t after closing the circuit,or after reversal. Then, since no current traverses thegalvanometer when a balance has been obtained, Zj andH are also the currents through CB and DB respec-tively. The difference of potential between A and C isthe same as between A and I) ; also the fall of potentialfrom (7 to ^ is the same as from D to B. Hence Biii + A-t!==^3«3,at Whence,
Electrical measurementsA laboratory manual . h their steadyvalues between consecutive reversals. The equation may be demonstrated as follows: Letii be the current through AC and 2*3 that through AD(Fig. 119), at the same instant t after closing the circuit,or after reversal. Then, since no current traverses thegalvanometer when a balance has been obtained, Zj andH are also the currents through CB and DB respec-tively. The difference of potential between A and C isthe same as between A and I) ; also the fall of potentialfrom (7 to ^ is the same as from D to B. Hence Biii + A-t!==^3«3,at Whence, at at at But BiB^ = BoBo^ is the condition of a balance with asteady current. The other condition for a balance withvarying currents is therefore ju^B^ = IjoBg.) ~ = —L2 B^ If one of these coefficients, as i,, is a standard of self- SELF-INDVCTlOJ^r AND MUTUAL INDUCTION. 257 induction, the equation gives the value of the a standard is shown in Fig. 120. It contains twocoils without iron joined in series, one of them fixed and. Fig. 120. the other movable about a vertical axis. The self-induction of the tAvo depends upon their relative position,and the scale at the top is graduated to read in milli-henrys. Since the self-induction of the standard isvariable, a balance can often be obtained for variablecurrents by changing the relative position of its twocoils. Its resistance, however, is only about ten ohms;and if the ratio of its smallest inductance to that of thecoil to be measured is greater than that of their relativeresistances, a balance can be effected onl}^ by addingnon-inductive resistance in series with the standard. 258 ELECTBICAL MEASUREMENTS. Incandescent lamps in parallel or in multiple series areconvenient for this purpose, since it is not necessary toknow their resistance. Alternating currents and an electrodynamometer maybe employed with advantage in this method (Art. 60).The entire current should pass through the field coil,and the suspended coil
Size: 1574px × 1588px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublisherbosto, bookyear1895
