A-B-C of Electricity

by Wm. H. Meadowcroft

In the closed-circuit batteries described, the electromotive force of each cell is about two volts, while the current varies from 1 to perhaps 50 ampères, according to the size of the zinc and carbon plates.

It would not matter if you made one cell as big as a barrel, nor if you put in a dozen carbons and zincs, the electromotive force would not exceed the volts mentioned for each type of battery, but the ampère capacity would be greater than in a smaller cell on account of the larger size of the carbon and zinc plates.

Internal Resistance.—There is one other point which affects the number of ampères which can be obtained from a closed-circuit battery, and that is whether there is a large or small internal resistance in the battery itself.

This depends upon the solution which is used and the arrangement of the plates.

If there is a high resistance in the battery itself (called "internal resistance"), the electricity must do work to overcome this resistance before it can get out of the battery to do useful work through the wires, and, consequently, the capacity in ampères is limited.

If, on the other hand, there is very little resistance in the battery, the current has very little work to flow to the wires leading from the battery, and we can get a larger quantity, or greater number of ampères.

Thus, you will see that while the closed-circuit battery is the stronger, and will do all that the open-circuit battery will do, and even more, in a short time the latter, though weaker, will do about as much work for the same amount of zinc and carbon as the former, but takes a much longer time.

BATTERIES FOR ELECTRIC LIGHT

As we have explained to you, closed-circuit batteries are used for producing incandescent electric lights in small numbers, as well as for running motors.

To operate incandescent lights, a number of batteries connected together are used. The number used depends upon the pressure which the lamps require to make them give the required light. We will now explain how the batteries are connected together for this purpose.