Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation. At high energy, the weak force and electromagnetic force are unified as a single electroweak force. Lightning is an electrostatic discharge that travels between two charged regions.
Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms that create molecules, and intermolecular forces. The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. There are numerous mathematical descriptions of the electromagnetic field. In Faraday’s law, magnetic fields are associated with electromagnetic induction and magnetism, and Maxwell’s equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents. The theoretical implications of electromagnetism, particularly the establishment of the speed of light based on properties of the “medium” of propagation (permeability and permittivity), led to the development of special relativity.
Electrodynamics is the study of phenomena associated with charged bodies in motion and varying electric and magnetic fields; since a moving charge produces a magnetic field, electrodynamics is concerned with effects such as magnetism, electromagnetic radiation, and electromagnetic induction, including such practical applications as the electric generator and the electric motor. This area of electrodynamics, often known as classical electrodynamics, was first systematically explained by the physicist James Clerk Maxwell. Maxwell’s equations, a set of differential equations, describe the phenomena of this area with great generality. A more recent development is quantum electrodynamics, which was formulated to explain the interaction of electromagnetic radiation with matter, to which the laws of the quantum theory apply. The physicists P. A. M. Dirac, W. Heisenberg, and W. Pauli were the pioneers in the formulation of quantum electrodynamics. When the velocities of the charged particles under consideration become comparable with the speed of light, corrections involving the theory of relativity must be made; this branch of the theory is called relativistic electrodynamics. It is applied to phenomena involved with particle accelerators and with electron tubes that are subject to high voltages and carry heavy currents. Electrodynamics is described by Maxwell’s Equations whose important consequences are:
(a). the electromagnetic nature of the light.
(b). the emission of electromagnetic waves by an oscillating dipole.
(c). the unification of electric and magnetic forces.
The concept of field in space and the distinction between directly observable field quantities and at best direct field potentials is at that stage still too vague to permit an immediate relativistic field approach to be plausible. In addition, the law of force between moving charges is considerably more complicated than that between point-like masses so that analogous procedure is not advisable. Nonetheless, Hamilton’s variational principle is of such basic significance that it permits, of course, the derivation of Maxwell’s equations as the Euler-Language equations of an appropriate variational principle.