Electromagnetism

In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interactions of atoms and molecules. Electromagnetism describes and relates the three distinct but closely intertwined phenomena of electricity, magnetism, and optics. In the study of electromagnetism these phenomena are described by the 3 sub-disciplines: electrostatics, magnetostatics, and electrodynamics. The electromagnetic force is responsible for many chemical and physical phenomena observed in daily life. The electrostatic attraction between atomic nuclei and their electrons holds atoms together. Electric forces also allow different atoms to combine into molecules. Meanwhile, magnetic interactions between the spin and angular momentum magnetic moments of electrons also play a role in chemical reactivity; such relationships are studied in spin chemistry. Electromagnetism also plays several crucial roles in modern technology: electrical energy production, transformation and distribution; light, heat, and sound production and detection; fiber optic and wireless communication; sensors; computation; electrolysis; electroplating; and mechanical motors and actuators. Electromagnetism has been studied since ancient times to explain the electric phenomena of lightning and static electricity and the magnetic phenomenon of the attraction between magnetized pieces of iron ore and of compasses. In the 18th and 19th centuries scientists developed the mathematical relationships between these phenomena and electric charges and currents. They also showed that electrical and magnetic phenomena were related and could create a self-sustaining electromagnetic waves which forms visible light and other forms of electromagnetic radiation including Gamma-rays, x-rays, ultraviolet, visible, infrared radiation, microwaves and radio waves. In the modern era, scientists continue to refine the theory of electromagnetism to account for the effects of modern physics, including quantum mechanics and relativity. The theoretical implications of electromagnetism, particularly the requirement that observations remain consistent when viewed from various moving frames of reference (relativistic electromagnetism) and the establishment of the speed of light based on properties of the medium of propagation (permeability and permittivity), helped inspire Einstein's theory of special relativity in 1905. Quantum electrodynamics (QED) modifies Maxwell's equations to be consistent with the quantized nature of matter. In QED, changes in the electromagnetic field are expressed in terms of discrete excitations, particles known as photons, the quanta of light. Mathematically, electromagnetism is described by electromagnetic fields. These are quantities that describe the electrical (electric field) and magnetic (magnetic field) influence at a given location and time.

A fundamental force

The electromagnetic force is the second strongest of the four known fundamental forces and has unlimited range. All other forces, known as non-fundamental forces. (e.g., friction, contact forces) are derived from the four fundamental forces. At high energy, the weak force and electromagnetic force are unified as a single interaction called the electroweak interaction. Most of the forces involved in interactions between atoms are explained by electromagnetic forces between electrically charged atomic nuclei and electrons. The electromagnetic force is also involved in all forms of chemical phenomena. Electromagnetism explains how materials carry momentum despite being composed of individual particles and empty space. The forces we experience when "pushing" or "pulling" ordinary material objects result from intermolecular forces between individual molecules in our bodies and in the objects. The effective forces generated by the momentum of electrons' movement is a necessary part of understanding atomic and intermolecular interactions. As electrons move between interacting atoms, they carry momentum with them. As a collection of electrons becomes more confined, their minimum momentum necessarily increases due to the Pauli exclusion principle. The behavior of matter at the molecular scale, including its density, is determined by the balance between the electromagnetic force and the force generated by the exchange of momentum carried by the electrons themselves.

Electromagnetic fields

The phenomena of electromagnetism is described mathematically using electromagnetic fields. An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarded as a combination of an electric field and a magnetic field. Because of the interrelationship between the fields, a disturbance in the electric field can create a disturbance in the magnetic field which in turn affects the electric field, leading to an oscillation that propagates through space, known as an electromagnetic wave. There are 6 mathematical quantities which are used to describe electromagnetic fields in 3 distinct cases. The electric field, E, and magnetic flux density, B are used to describe the electromagnetic fields in cases where all the charges are known directly such as the electromagnetic field in a vacuum. To describe the case where the charges inside of a material respond to applied electric and magnetic fields, it is useful to define the electric displacement field, D and magnetic field strength, H, in addition to E and B. Finally, it is sometimes useful to describe electromagnetic fields not in terms of force but in terms of potential energy and momentum. In this case, the electromagnetic field is represented by the electric potential, V, and the magnetic vector potential, A, respectively.

Force on an electric charge due to electromagnetic fields

The force, F. on a charge particle of charge q moving at speed v in an electromagnetic field is given by the Lorentz force(SI definition of quantities):

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