. Carnegie Institution of Washington publication. 64 DISPLACEMENT INTERFEROMETRY BY Following the usual theory, if L has the form 47rw2/ (1/nA), n being the number of turns of wire around an electromagnet of length /, area A, and permeability /ji, and if the coefficient of mutual induction of the transformer is M= \/LiLt, and if e = e0 sin wt is the impressed voltage, the secondary voltage will be cos (cof — Hence the secondary current, when L2Rz and C2 are there inserted, is e cos (at — ip\ — o^o) where = tan = tan This is further to be modified with reference to the amplitude and phase of th
. Carnegie Institution of Washington publication. 64 DISPLACEMENT INTERFEROMETRY BY Following the usual theory, if L has the form 47rw2/ (1/nA), n being the number of turns of wire around an electromagnet of length /, area A, and permeability /ji, and if the coefficient of mutual induction of the transformer is M= \/LiLt, and if e = e0 sin wt is the impressed voltage, the secondary voltage will be cos (cof — Hence the secondary current, when L2Rz and C2 are there inserted, is e cos (at — ip\ — o^o) where = tan = tan This is further to be modified with reference to the amplitude and phase of the extraneous coupling. 46. Direct telephonic induction.—The influence of the oscillating magnetic field on the telephone is much more pervasive than one is apt to suppose. The effect, moreover, is particularly marked if the telephone is open, , with no connection between the clamps. A coil of high resistance of telephone wire, implying many turns, is naturally preferable. The stray vibrating field produced by a small electromagnet (say inch iron, 2 inches long) is quite audible even beyond 50 cm. from the electromagnet. The degree of response depends, moreover, on the orientation (fig. 70) of the telephone relative to the M M I*. d' electromagnet E. If we take the three cardinal positions of the plane of the coil or the diaphragm, the vertical positions e, d, f, and the fore-and-aft hori- zontal positions h, g, i, have their maximum response in the plane of symmetry gdE. The right-and-left horizontal positions d", b, a, c, d' give minimum response (telephone silent) in this plane (Ed), with maxima at symmetrical positions, 6 and c. Near E (20 cm.) the sounds may be quite loud. Although all telephones show the phenomenon pretty well, since it is more distinct on open circuit (which implies a current oscillating from clamp to clamp) it would be well worth while to wind a telephonic bobbin provided with a capacity for the particular purpose of catching the st
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