Electric Charge

The existence of electricity, the phenomenon associated with stationary or moving electric charges, has been known since the Greeks discovered that amber, rubbed with fur, attracted light objects such as feathers. Ben Franklin proved the electrical nature of lightning (the famous key experiment) and also established the conventional use of negative and positive types of charges.lightn

It was also known that certain materials blocked electric charge, called insulators, such as glass or cork. Other materials transferred electric charge with ease, called conductors, such as metal. leyden_jarBy the 18th century, physicist Charles Coulomb defined the quantity of electricity later known as a coulomb, and determined the force law between electric charges, known as Coulomb’s law.

Coulomb’s law is similar to the law of gravity in that the electrical force is inversely proportional to the distance of the charges squared, and proportional to the product of the charges.By the end of the 18th century, we had determined that electric charge could be stored in a conducting body if it is insulated from its surroundings. The first of these devices was the Leyden jar. consisted of a glass vial, partly filled with sheets of metal foil, the top of which was closed by a cork pierced with a wire or nail. To charge the jar, the exposed end of the wire is brought in contact with a friction device. Modern atomic theory explains this as the ability of atoms to either lose or gain an outer electron and thus exhibit a net positive charge or gain a net negative charge (since the electron is negative). Today we know that the basic quantity of electric charge is the electron, and one coulomb is about 6.24×1018 electrons.

The battery was invented in the 19th century, and electric current and static electricity were shown to be manifestations of the same phenomenon, i.e. current is the motion of electric charge. Once a laboratory curiosity, electricity becomes the focus of industrial concerns when it is shown that electrical power can be transmitted efficiently from place to place and with the invention of the incandescent lamp.

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