Handbook of projection for theatre managers and motion picture projectionists ([1922])

MANAGERS AND PROJECTIONISTS of zinc of approximately the same superficial area, and the whole will constitute the simplest form of electric generator known, the assemblage constituting what is known as a "wet" battery. If we make electrical connection between the copper and zinc of such a battery, current, generated by chemical action, will flow from copper to zinc, the former being positive (+) and the latter negative ( — ). A well proportioned battery of this sort will generate about one volt pressure and several amperes of current while it lasts. In theory it would be possible to join sufficient of these batteries to produce almost any desired voltage and amperage, but in practice this would be impractical. The use of generating batteries is almost entirely confined to light work, such as the ringing of bells and buzzers, the telegraph and like service where comparatively little energy is required. For power purposes we depend upon the dynamo, or "generator," as it is usually termed. The dynamo depends for its action primarily upon magnetism, and the generation of electric energy in the armature of a dynamo is based upon the following law : "If an electric conductor in the form of a closed circuit be moved in a magnetic field in such a way that lines of force are cut, a current of electricity will be generated therein, which same will flow in a direction at right angles to the line of motion." See Hawkins' Electrical Guides, Vol. 1, Pages 125 to 136, for a detailed explanation of this law and its operation. In Fig. 1 we see the diagrammatic representation of the simplest possible form of electric dynamo. N and S are respectively the north and south poles of a permanent magnet, between and around the poles of which flow magnetic lines of force, represented by the dotted lines. Within the magnetic field thus formed is copper wire A — B, bent Figure