The first proper understanding of the electricity dates to the 18th century, when a French physicist, Charles Coulomb, showed that the electrostatic force between electrically charged objects follows a law similar to Newton's law of gravitation. Coulomb found that the force F between one charge q₁ and a second charge q₂ is equal to the product of the charges divided by the square of the distance r between them, or F = q₁ q₂ /r . The force can be either attractive or repulsive, because the source of the force, electric charge, exists in two varieties, positive and negative. The force between opposite charges is attractive, whereas bodies with the same kind of charge experience a repulsive force. The science of electricity is concerned with the behavior of aggregates of charge, including the distribution of charge within matter and the motion of charge from place to place. Different types of materials are classified as either conductors or insulators on the basis of whether charges can move freely through their constituent matter. Electric current is the measure of the flow of charges; the laws governing currents in matter are important in technology, particularly in the production, distribution, and control of energy.

The concept of voltage, like those of charge and current, is fundamental to the science of electricity. Voltage is a measure of the propensity of charge to flow from one place to another; positive charges generally tend to move from a region of high voltage to a region of lower voltage. A common problem in electricity is determining the relationship between voltage and current or charge in a given physical situation.

Excerpt from the Encyclopedia Britannica without permission.