Electric Charge and Electricity

Electricity is a set of physical phenomena arising from electric charge, a fundamental property of matter. Charge comes in two kinds, conventionally called positive and negative. Protons in the nucleus of an atom carry positive charge and electrons carry an equal but negative charge, while neutrons carry none. Objects with the same kind of charge repel one another, and objects with opposite charges attract. An atom that gains or loses electrons becomes a charged particle called an ion.

A central principle is the conservation of electric charge: charge is never created or destroyed, only transferred from one object to another. Rubbing two materials together, for example, can move electrons from one to the other, leaving one positively charged and the other negatively charged by an equal amount. Materials differ in how readily charge moves through them. In conductors, such as metals, electrons move freely, while in insulators they are bound in place. Bringing a charged object near a conductor can rearrange its charges, producing an induced charge without contact.

The force between charges is described by Coulomb's law, which states that the force grows with the size of the charges and weakens with the square of the distance between them. The charge itself is measured in a unit called the coulomb. To describe the influence a charge exerts on its surroundings, physicists use the idea of an electric field, a vector quantity defined at every point in space as the force that would act on a small positive test charge placed there. The field points away from positive charges and toward negative ones.

Frequently asked questions

What are the two kinds of electric charge?

Charge is positive or negative. Protons carry positive charge and electrons carry negative charge of equal size. Like charges repel and opposite charges attract.

What does conservation of charge mean?

It means charge cannot be created or destroyed, only moved between objects. When one object gains charge, another loses an equal amount.

What is an electric field?

An electric field is a region around a charge where another charge would feel a force. It is a vector defined as the force per unit charge on a small positive test charge.