Electromagnetism describes the interaction of charged particles with electric and magnetic fields. It can be divided into electrostatics, the study of interactions between charges at rest, and electrodynamics, the study of interactions between moving charges and radiation. The classical theory of electromagnetism is based on the Lorentz force law and Maxwell’s equations. Light is an oscillating electromagnetic fieldthat is radiated from accelerating charged particles. Thus, all of optics, the study of the nature and propagation of light, can be reduced to electromagnetic interactions. Two major fields of optics are geometric optics or “classical optics”, and physical optics which studies the electromagnetic properties of light to achieve greater understanding of phenomena such as interference, diffraction, and polarization.

A more recent development is quantum electrodynamics, which incorporates the laws of quantum theory in order to explain the interaction of electromagnetic radiation with matter. Relativistic electrodynamics accounts for relativistic corrections to the motions of charged particles when their speeds approach the speed of light. It applies to phenomena involved with particle accelerators and electron tubes carrying high voltages and currents.