Text: Theory of Electrification

1. Historically there have been two outstanding theories of electrification: the one-fluid theory of Benjamin Franklin and the two-fluid theory of Charles Du Fay,. According to the two-fluid theory, all objects contain equal amounts of two fluids. When two different substances are rubbed together, one kind of fluids (positive0 is spread over one object and the other kind of fluid (negative0 over the other.

2. According to the one-fluid theory of Franklin, all bodies contain a certain specified amount of an “electric fire” or fluid to keep them in an uncharged or neutral state. When two objects are rubbed together; one accumulates an excess of fluid and becomes positively charged while the other loses fluid and becomes negatively charged. To Franklin we owe the terms “plus” and “minus”, “positive” and “negative” electricity.

3. We consider both of these theories to be in part correct, for now we know the mechanism by which bodies become electrified by friction. The modern theory is based upon the principle already put forward – that all substances are made of atoms and molecules. Each atom contains a nucleus having a known amount of positive charge. This positive charge is due to the presence in the nucleus of a certain number of protons. All protons are alike and have the same mass and positive charge. Around every atomic nucleus there are a number of negatively charged particles, called electrons.

4 .While protons are much smaller than electrons in size, they contain the bulk of the mass of every atom. One proton, for example, weighs nearly two thousand times as much as an electron. The electrons therefore are light particles or objects around a small but relatively heavy nucleus.

5. Individually atoms or large groups of atoms and molecules have an affinity, an attraction for additional electrons over and the exact number which will just neutralize the positive charges of the nuclei. This attraction of the atoms for more than a sufficient number of electrons varies considerably from atom to atom and substance to substance. When, therefore, two different substances are brought onto contact, the substance with greater electron affinity seizes nearby electrons from the other, and thus acquires a net negative charge. Such is the case, for example, with rubber and amber when they are rubbed with fur. Having astrong affinity for electrons, both of these solids become strongly negative, whereas the fur becomes deficient of electrons and thereby positively charged.