Electrostatics and Coulomb's Law

Electrostatics is the branch of physics concerned with electric charges at rest and the forces, fields and potentials they produce. Matter contains positive and negative charges, normally balanced, but rubbing or contact can transfer electrons and leave objects with a net charge. Like charges repel and unlike charges attract, a behaviour that explains everyday effects such as a balloon clinging to a wall or hair standing up after combing.

The force between two point charges is described by Coulomb's law, formulated by Charles-Augustin de Coulomb in the eighteenth century. It states that the force is proportional to the product of the two charges and inversely proportional to the square of the distance between them. The force acts along the line joining the charges, and its strength also depends on the medium in which the charges sit. This inverse-square form closely parallels Newton's law of gravitation.

To handle distributed charges, electrostatics uses the idea of an electric field, defined as the force per unit positive test charge at a point in space. Field lines provide a visual picture: they point away from positive charges and toward negative ones, and their density indicates field strength. Closely related is electric potential, measured in volts, which represents the energy per unit charge. These concepts underpin practical topics such as capacitance, shielding and the operation of devices that store or steer charge.

Frequently asked questions

What does Coulomb's law describe?

It gives the electrostatic force between two point charges, which grows with the size of the charges and falls off with the square of the distance separating them.

How does an electric field differ from electric potential?

An electric field is the force per unit charge and has direction, while electric potential is the energy per unit charge and is a scalar measured in volts.

Why do objects become charged by rubbing?

Friction transfers electrons from one material to another. The material that gains electrons becomes negatively charged and the one that loses them becomes positively charged.