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.

    422/502 page 402
    conductors like glass and sealing-wax, as well as with con- ductors like copper and zinc. 384. Definition of Electromotive Force.—But whatever may be the true origin of the electrical separation which takes place in a voltaic battery, it is the tendency of the separated electricities to unite that produces the current, so that the in- tensity of the electrical separation becomes the measure of what we may term the electromotive force which is often abbreviated to E. M. F. 385. Law of E. M. F's.—Wheatstone devised a means of measuring the electromotive force of different combinations. He found from his experiments that if platinum and an amal- gam of potassium be used as the two plates of a battery, the electromotive force or intensity of electrical separation may be called 69. He also found that the electromotive force be- tween a platinum and a zinc plate is 40 ; While that between a zinc and an amalgamated potassium plate is 29. We derive from this experiment a very interesting result. Thus if platinum be our negative and zinc our positive element, we get 40 as the value of our electromotive force ; again, if zinc be our negative and potassium our positive ele- ment, we get 29 ; but if, instead of going in two steps from platinum to potassium, we go in one step, and make a com- bination of these two metals, we get 69 at once. In fine, the electromotive force between any two metals is equal to the stun of the electromotive forces between all the intei-vcning metals. 386. The E. M. F. Series.—The various metals in the following table are classified according to their order in the electromotive series. Thus we have— Table No. 41.—Electromotive Series. Electro-positive. Lead. Tin. Iron. Potassium. Zinc. Cadmium. Nickel. Bisnuuh. Antimony. Copper. Silver. Gold. Platinum. Elect ro-ncgative.
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