Arrangement of Cells in a Battery; Series Grouping.Whenever several cells are to be grouped in a battery, the question of how they shall be coupled together becomes an important one. As horses can be hitched to a wagon, either one behind the other (tandem) or side by side (abreast) so cells can be coupled either in series or in parallel. When two or more cells are coupled in series, the copper of one is joined to the zinc of the next, while the outside copper and zinc form the terminals of the battery, as A and B in Fig. 1.
For this grouping the E. M. F. of one cell is added to that of the next, and the total internal resistance is the sum of the internal resistances of all the cells; hence Ohm's Law will be written
in which S is the number of cells in series; E, the E. M. F. of each cell; b, the internal resistance of each cell; and R, the resistances of all conductors and instruments through which the current passes.
EXAMPLE. - Suppose 4 cells to be coupled in series, the E. M. F. of each to be 1.02 volts, and the internal resistance of each 2.4 ohms, what current will they send through an external resistance of 27 ohms?
