The ampere (formerly called the “Weber”) is the measure of strength of current. If an E. M. F. of one volt be applied to send a current through a resistance of one ohm, the strength of current will be one ampere. That is to say, the strength of a current in amperes varies directly as the E. M. F. applied to produce it, and inversely as the resistance of the circuit.
The watt or practical unit of work (or rather, the rate of doing work) is equal to 10,000,000 ergs per second, or to the work produced in one second by one ampere of current of an E. M. F. of one volt, acting through the resistance of one ohm.
The practical electrical units are called after the eminent scientific investigators whose names they bear.
BATTERIES.
The portion of the copper plate (or carbon) from which the current flows through the wire is called the positive pole (sometimes anode), and the zinc plate the negative pole (sometimes cathode).
Elements, or the parts that produce current, are usually understood as the lower portion of the cell contents, in which the plates are immersed. When the term “pole” is reversed, the zinc being the positive element, and the copper or carbon the negative element, it will be noted current flows from positive pole (copper or carbon) and returns by the negative (or zinc) pole.
The bubbles of hydrogen gas liberated at the negative element (copper or carbon) resist the passage of the current, and being readily oxidizable, will set up an opposing E. M. F.
A battery in this condition is polarized—that is, neutralized—and must be renewed.
The E. M. F. of a cell is equivalent to the difference of potential between its electrode when unconnected, and is independent of the size of the elements, and is determined solely by the materials of which it is constructed.
The difference of potential between zinc and carbon being greater than that between zinc and copper, a cell of greater E. M. F. will result from zinc and carbon.