Electromagnetism

Electromagnetism is the physics of the electromagnetic field. This is a field, encompassing all of space, composed of mutually dependent time varying electric and magnetic fields. The term "electromagnetism" comes from the fact that the electric and magnetic fields are closely intertwined, and, under most circumstances, it is impossible to consider the two separately.

Origins of electromagnetic theory

The scientist William Gilbert proposed, in his De Magnete (1600), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects. Mariners had noticed that lightning strikes had the ability to disturb a compass needle, but the link between lightning and electricity was not confirmed until Franklin's proposed experiments (performed initially by others) in 1752. One of the first to discover and publish a link between man-made electric current and magnetism was Romagnosi, who in 1802 noticed that connecting a wire across a Voltaic pile deflected a nearby compass needle. However, the effect did not become widely known until 1820, when Ørsted performed a similar experiment. Ørsted's work influenced Ampère to produce a theory of electromagnetism that set the subject on a mathematical foundation.

Related Topics:
William Gilbert - De Magnete - 1600 - Franklin's - 1752 - Romagnosi - 1802 - Voltaic pile - Compass - 1820 - Ørsted - Ampère

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An accurate theory of electromagnetism, known as classical electromagnetism, was developed by various physicists over the course of the 19th century, culminating in the work of James Clerk Maxwell, who unified the preceding developments into a single theory and discovered the electromagnetic nature of light. In classical electromagnetism, the electromagnetic field obeys a set of equations known as Maxwell's equations, and the electromagnetic force is given by the Lorentz force law.

Related Topics:
Classical electromagnetism - Physicist - 19th century - James Clerk Maxwell - Maxwell's equations - Lorentz force law

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One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with classical mechanics, but it is compatible with special relativity. According to Maxwell's equations, the speed of light is a universal constant, dependent only on the electrical permittivity and magnetic permeability of the vacuum. This violates Galilean invariance, a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a luminiferous aether through which the light propagates. However, subsequent experiments efforts failed to detect the presence of the aether. In 1905, Albert Einstein solved the problem with the introduction of special relativity, which replaces classical kinematics with a new theory of kinematics that is compatible with classical electromagnetism.

Related Topics:
Classical mechanics - Special relativity - Speed of light - Electrical permittivity - Magnetic permeability - Vacuum - Galilean invariance - Luminiferous aether - 1905 - Albert Einstein

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In another paper published in that same year, Einstein undermined the very foundations of classical electromagnetism. His theory of the photoelectric effect (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities, which later came to be known as photons. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the ultraviolet catastrophe presented by Max Planck in 1900. In his work, Planck showed that hot objects emit electromagnetic radiation in discrete packets, which leads to a finite total energy emitted as black body radiation. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of quantum mechanics, which, when formulated in 1925, necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the 1940s, is known as quantum electrodynamics (or "QED"), and is one of the most accurate theories known to physics.

Related Topics:
Photoelectric effect - Photon - Ultraviolet catastrophe - Max Planck - 1900 - Electromagnetic radiation - Energy - Black body radiation - Quantum mechanics - 1925 - 1940s - Quantum electrodynamics

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