Electricity is the name given to phenomena caused by the accumulation or motion of electrically charged particles. The effects resulting from the accumulation of positive or negative charge are termed "static electricity," while the effects resulting from the motion of charged particles are termed "current electricity."
Lightning is an electrical phenomenon that has occurred on Earth ever since the planet acquired an atmosphere. It consists of spectacular current discharges between regions of positive and negative charge formed by atmospheric convection, such as occurs in storm clouds and around erupting volcanoes.
Early experiments
The first recorded observations of electrical phenomena occurred more than 2,500 years ago: in ancient Greece, Thales of Miletus noted that certain substances, when rubbed with cloth, were able to attract lightweight objects. One such substance is amber, a natural resin whose Greek name—elektron—is the root of the word electricity. The form of electricity generated by rubbing surfaces together is called triboelectricity. The Greeks associated triboelectricity with magnetism, which they had observed in the properties of magnetite ore, since both phenomena give rise to attractive and repulsive forces between objects that are not in physical contact.
In the mid-16th century, the Italian physician Jerome Cardan studied the relationship between magnetic and electrostatic forces. In 1551, he proposed that electricity was a type of fluid. In 1600, William Gilbert, an English physician investigating electromagnetic phenomena, conducted extensive research into triboelectrification. He classified substances as good or poor electrifiers—classifications that correspond to modern insulators and conductors, respectively. The theory of electrical fluid was further developed by the French scientist Charles du Fay. In 1733, du Fay proposed that there were two types of electrical fluid, and the phenomena of static electricity occurred when the two are out of balance.
In 1747, Benjamin Franklin, known for his celebrated experiments with kites flown during thunderstorms and with an early type of capacitor called a Leyden jar, proposed that there was only one electrical fluid that moved through conductors. According to this theory, it is buildup or depletion of this fluid beyond that normally found in an object that caused the effects of positive or negative charge.
Static electricity
The distinction between positive and negative electricity came about because some pairs of electrified substances attract one another, while others exert mutual repulsion. This behavior mirrors that of magnets: the north pole of a magnet will repel another magnet’s north pole, just as two south poles repel one another, but a north pole and a south pole will attract one another.
The quantitative study of static electricity began in the second half of the 18th century when two scientists independently discovered a relationship between the electrostatic force between two charged objects, the size of their charges, and the distance between them. The discovery was made in 1767 by Joseph Priestley, a British chemist and physicist, then in 1785 by Charles Coulomb, a French physicist. The mathematical expression of the relationship became known as Coulomb’s law and the standard unit of electrical charge the coulomb.
Coulomb and Priestley found that the force between two charged objects varies with the reciprocal of the square of the distance between the objects. The formula has stood essentially unchanged to this day—a tribute to the experimental precision of both scientists.
