Electric Current and Ohm's Law

                               Nature of Electricity

It is comparatively easy to describe what electricity can do than to give a simple and direct answer to the question: What exactly is meant by electricity ?  Electricity has become such a universal medium for transmission and utilization of energy that almost every one is familiar with its innumerable uses right from the earliest childhood. Electric energy is variously utilized as for lighting, transportation, communication, for operating electric furnaces, elevators and for driving various kinds of machine tools etc. It can be easily stored and concentrated to produce extremely high temperatures as in welding and electric furnaces, are lights and spark plugs etc.

Turning back to the question regarding the nature of electricity, it may be noted that ancient Greeks were the first to observe that when amber is rubbed against a piece of silk cloth, it attracts light objects like small pieces of paper etc. The agency that endowed this attracting property to amber was given the name of electricity by Gilbert in 1600 A.D. The name electricity is derived from the word electron which is the Greek name of amber.

To explain the few observed phenomenon about electricity, Benjamin Franklin advanced, in 1749, what was called on Fluid Theory of electricity. According to this theory, electricity was assumed to be a sort of an invisible and intangible fluid which was associated with matter in different degrees. The normal state of matter was associated with a certain definite amount of this fluid. Any disturbance of this assumed normal distribution of fluid was supposed to result in the body being either positively or negatively charged corresponding to an excess or deficit of this normal amount of fluid. This theory was successful in explaining the production of positive and negative electricity when two bodies are rubbed together. Because, according to this theory, rubbing of two bodies together led to an unequal redistribution of their fluids whose total sum was supposed to remain constant. One body which got more of this fluid became positively charged and the other which got less became negatively charged.

It will be noted that this theory does not assume two types of fluids, but simply two states of electrification resulting from an excess or deficit of the same fluid. This theory, however, did not hold ground for long since it could not satisfactorily explain many electrical phenomena including induction.

In the year 1735, Dufay advanced the Two Fluid Theory which was later modified and restated in a more satisfactory manner by Symmer in 1759. According to this theory, two different types of fluids resided simultaneously in matter corresponding to two states of electrification positive and negative. The type and degree of electrification was measured by the excess of one type of fluid over the other. The normal non-electrical state of matter was assumed to be due to the presence of equal quantities of these two fluids which neutralized each other.

This theory was successful for some time, but was, later on, discarded because it was based on the untenable assumption of two invisible fluids present in the matter and it was found inadequate to fully explain many of the facts about electricity discovered afterwards.