This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 edition. Excerpt: ...superimposed frequencies, ranging from perhaps 100 to 1500; for wireless telegraphy and telephony the frequency may be between 20,000 and several hundred thousand; two small metallic spheres charged with electricity of opposite kinds will, if brought close enough together, exchange and neutralize ...
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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 edition. Excerpt: ...superimposed frequencies, ranging from perhaps 100 to 1500; for wireless telegraphy and telephony the frequency may be between 20,000 and several hundred thousand; two small metallic spheres charged with electricity of opposite kinds will, if brought close enough together, exchange and neutralize charges; the discharge current is oscillatory in character and may be of a frequency of several billions of cycles per second. Generally an alternating current is sinusoidal in form. If i = instantaneous value of current; Jmax = maximum value of current; p = 27rXfrequency of current; we have i=Lmx COS pt. An alternating current generator is generally designed so that its wave form may be expressed by the formula e = JSmax COS pi. Whether or not a generator gives such a wave form depends upon the shape of the air gap between armature and pole face and also upon the distribution of armature winding. Whenever a sine wave of E.M.F. is applied to a circuit, the current which is caused to flow is also a sine wave (neglecting distorting effects of hysteresis, dielectric loss in condensers, etc.). If the circuit is non-inductive the E.M.F. and current waves are in phase, i.e., the maximum and minimum values of the two waves occur simultaneously. If, however, the circuit offers inductance or capacity reaction, or both, the current may either lag or lead the E.M.F. in phase, depending upon which reaction predominates. These reactions are more fully analyzed in the discussion of Ex. 2. The question arises how much power is used in a-circuit in which an alternating current is flowing? The reactions which are offered to the flow of the current are of two general types, conservative or non-dissipative, and non-conservative or dissipative. The product of the...
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