(B) Lay the ends of the metal, or other thick conductor, upon M P-A and M P-B. Compare the new reading of G V with that in part (A).
(C) Remove the conductor used to short circuit G V, take the reading in degrees, then touch M P-A to M P-B; watch G V.
295. Short Circuits are very apt to occur unless care is taken. Do not allow uninsulated wires to touch each other. As shown by the above experiment, practically the whole of the current may be side-tracked by a shunt of low resistance. A galvanic cell is short-circuited by connecting the plates directly by a wire or other conductor.
CHAPTER XVII.
ELECTROMOTIVE FORCE.
296. Electromotive Force. It has been stated that a galvanic cell has the power to charge one of its plates positively and the other negatively; this power is called electromotive force, and, for short, E. M. F. is written. The E. M. F. of a cell depends upon the kinds of plates used and their condition, the chemicals used in the exciting fluids, etc. The greater the E. M. F. of a cell the greater its power to force the current through wires, etc. The E. M. F. of a cell does not depend upon the size of its plates, as will be seen by later experiments.
297. Unit of E. M. F.; The Volt. A certain amount of E. M. F. has been taken as the standard, and, in honor of Volta, it has been called the volt. The E. M. F. of the two-fluid cell used in [Exp. 113] is not far from 1 volt. If a certain cell has the power to keep up twice the difference of potential between its terminals that the Daniell cell has, we say that it has an E. M. F. of about 2 volts.
Voltmeters are instruments to measure E. M. F.
EXPERIMENT 116. To see if the E. M. F. of a cell depends upon the materials used in its construction.