Electric current

When a charge of negative electricity, i.e. of electrons, is put at a point on a conductor, that point is momentarily at a potential lower than the potential of the rest of the conductor, the electrons flowing along the conductor until all its parts are at the same potential. In case a positive charge is put at a point, the electrons move to that point, the potential at the point being raised, electrons will flow awards that point until all points of the conductor are gain at the same potential.

If a steady potential difference is maintained by some leans between two points in a metallic conductor as between the two ends of a copper wire, there will be a steady stream of electrons flowing from the end at low potential to the one at high potential. (Of course, you will remember that the terms "stream" and "flow" are synonyms). This stream (or flow) of moving electrons is one form of electric current. The magnitude of the current is the quantity of electric charge carried by the electrons in a unit of time through any cross-section of the conductor. By a convention adopted before electrons were discovered, we usually say that the electric current in such a conductor flows from points of high potential to those of low potential or in the direction of the potential gradient. However, saying that a current is flowing from point A to point B in a metallic conductor, we really mean that electrons are flowing from point B to point A. Such a current does not change the chemical constitution the conductor.

The conductor being a solution, say, of salt in water, the molecules of salt are ionized, both positive and negative ions moving under the influence of the electric field, this case the sum of the quantities of positive and negative electricity, carried by the ions in a unit of time through any cross-section of the liquid, constitutes the electric current. Such a current is usually accompanied by a chemical action.

An electric current passes through a gas only when the molecules or atoms of the gas are ionized. Here again, both the positive and the negative ions or electrons move under the influence of the electric field, the sum of the quantities of positive and negative electricity carried by the ions in a unit of time through any cross-section of the gas constituting the electric current.

Speaking of electricity in motion, reference should be made to Volta, professor of natural history, at the University of Pavia, Italy. Volta was a clever experimentalist, with a thorough knowledge of all that had been done by others in the field of electricity, a great scientist. In 1800, he constructed the first source of steady, continuous current— the voltaic pile. The voltaic pile was the first battery transforming chemical energy into electrical energy. It is to this invention that we owe the development of modern electrical science and industry.