Electrodynamics

Electric charges interact via the electric and magnetic fields they produce. Electrodynamics is the study of the laws governing these interactions. The phenomena of electricity and of magnetism were once taken to constitute separate subjects. By the beginning of the nineteenth century they were recognized as closely related topics and by the end of that century electromagnetic phenomena had been unified with those of optics. Classical electrodynamics provided the foundation for the special theory of relativity, and its unification with the principles of quantum mechanics has led to modern quantum field theory, arguably our most fundamental physical theory to date.