Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

    449/502 page 429
    LESS. XLViii ELECTRICITY IN MOTION There is, however, a commutator, /, the object of wliich is to make the alternate currents of the coils pass from these coils through the connecting wires always in the same direction. ■413. Dynamos.—In the modern machines known as dynamos., electro-magnets instead of permanent magnets are used. These machines are of two chief types : (i) Direct current machines tvhich are provided with a commutator; (2) Alternate current machines in which the direction of the current rapidly changes, owing to no commutator being used. Powerful machines on this principle form a very convenient arrangement for obtain- ing current electricity, and electrical energy can be produced economically by their means, and applied to a variety of useful purposes. 414. Ruhmkorff’s Coil. — In RuhmkorfTs coil the ordinary current is changed by induction into one which possesses very great electro-motive force. We have in the centre of this coil a core of a bundle of wires of soft iron, and a current from several Grove's or other cells is made to pass round this core in such a manner as to transform it when the current pa.sses into a powerful electro-magnet. The coil of wire through which the current p.asses is called the primary coil (see Fig. Outside of this, ;md insu- lated from the primary, we have ;i secondary coil, consisting of a large quantity of fine wire well insulated, sometimes 40 or 50 miles of wire being used for this purpose. In such machines there is a self-acting arrangement, by winch the primary circuit is made :ind broken, .and the .soft
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image