Ann., 1834, 31; 18 35, 34) among other results led him to the statement of the law by means of which the direction of the induced current can be predicted from the theory of Ampere, the rule being that the direction of the induced current is always such that its electrodynamic action tends to oppose the motion which produces it.
Electrodynamic A mmeters.
Now the electric force (P,Q,R) is the force acting on the electrons of the medium moving with velocity v; consequently by Faraday's electrodynamic law (P,Q,R) = (P',Q' - vc, R'+vb) where (P',Q',R') is the force that would act on electrons at rest, and (a,b,c) is the magnetic induction.
If v varies with respect to locality, or if there is a velocity of convection (p,q,r) variable with respect to direction and position, and analytical expression of the relation (ii) assumes a more complex form; we thus derive the most general equations of electrodynamic propagation for matter treated as continuous, anyhow distributed and moving in any manner.
These results constitute a far-reaching development of the modern or electrodynamic theory of the aether, of which the issue can hardly yet be foreseen.
Electromagnetic voltmeters may therefore be thermal, electromagnetic or electrodynamic. As a rule, electromagnetic voltmeters are only suitable for the measurement of relatively small potentials - o to 200 or 300 volts.
Hence we may classify ammeters into (1) Thermal; (2) Electromagnetic, and (3) Electrodynamic instruments.
1 d-p2T,T„' Hence an electrodynamic wattmeter, applied to measure the electrical power taken up in a circuit when employing alternating currents, gives absolutely correct readings only in two cases - (i.) when the potential circuit of the wattmeter and the power-absorbing circuit have negligible inductances, and (ii.) when the same two circuits have equal time-constants.
In 1846 Weber announced his famous hypothesis concerning the connexion of electrostatic and electrodynamic phenomena.
His work on the electrodynamic qualities of metals, thermo-electricity, and his contributions to galvanometry, were not less massive and profound.
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