Electromotive Force Arising During the Rotation of Conductors

(Tolman and Stewart. The Electromotive Force Produced by the Acceleration of Metals. Phys. Rev. 8, 1916, p. 97, and by the same authors, The Mass of the Electric Carrier in Copper, Silver and Aluminium. Phys. Rev. 9, 1917, p. 164.)

The electrical conductivity of metals is explained, according to J. J. Thomson’s first theory of conductivity, by the existence of an electron gas. It is clear that, when an (uncharged) metallic disk is rotated, the free electrons of the metal

tend, under the influence of the centrifugal force, toward the periphery, which must therefore become negatively charged.

Tolman and Stewart, in order to measure this effect, use a wire ring 47 cm long, the ends of which are connected by means of a sliding contact to a galvanometer of the d’Arsonval type. When the ring is rotated, the galvanometer gives a deflection equal to that calculated theoretically.

Simple considerations give the formula \(Q=\dfrac{mvl}{eR}\), where \(R\) is the resistance of the ring, \(l\) its length, \(v\) the velocity, and \(Q\) the quantity of electricity that has passed through the galvanometer. Thus we have a new method for determining \(\dfrac{e}{m}\) (the ratio of charge to mass). The values obtained are of the order previously established.

As early as 1882, Colley successfully applied the same method of centrifuging to electrolytes (a solution of cadmium iodide). As is known, Lebedev, in his unfinished magnetometric investigation of rotating bodies, makes use of the same idea of centrifugal displacements.

E. V. Plyushch.