Introduction to electromagnetism: Difference between revisions

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{{about|a conceptual understanding of the topic|a more detailed mathematical treatment|electromagnetic field}}

'''[[Electromagnetism]]''' is one of the [[Fundamental interaction|fundamental forces]] of nature. Early on, [[electricity]] and [[magnetism]] were studied separately and regarded as separate phenomena. [[Hans Christian Ørsted]] discovered that the two were related – [[electric current]]s give rise to magnetism. [[Michael Faraday]] discovered the converse, that magnetism could [[electromagnetic induction|induce]] electric currents, and [[James Clerk Maxwell]] put the whole thing together in a unified theory of electromagnetism. [[Maxwell's equations]] further indicated that [[electromagnetic wave]]s existed, and the experiments of [[Heinrich Hertz]] confirmed this, making [[radio]] possible. Maxwell also postulated, correctly, that [[light]] was a form of electromagnetic wave, thus making all of [[optics]] a branch of electromagnetism. [[Radio wave]]s differ from light only in that the [[wavelength]] of the former is much longer than the latter. [[Albert Einstein]] showed that the [[magnetic field]] arises through the [[Classical electromagnetism and special relativity|relativistic motion]] of the [[electric field]] and thus magnetism is merely a side effect of electricity. The modern theoretical treatment of electromagnetism is as a [[quantum field]] in [[quantum electrodynamics]].

In many situations of interest to [[electrical engineering]], it is not necessary to apply quantum theory to get correct results. [[Classical physics]] is still an accurate approximation in most situations involving [[macroscopic]] objects. With few exceptions, quantum theory is only necessary at the [[atomic scale]] and a simpler classical treatment can be applied. Further simplifications of treatment are possible in limited situations. [[Electrostatics]] deals only with stationary [[electric charge]]s so magnetic fields do not arise and are not considered. [[Permanent magnet]]s can be described without reference to electricity or electromagnetism. [[Circuit theory]] deals with [[electrical network]]s where the fields are largely confined around current carrying [[Electrical conductor|conductors]]. In such circuits, even Maxwell's equations can be dispensed with and simpler formulations used. On the other hand, a quantum treatment of electromagnetism is important in [[chemistry]]. [[Chemical reaction]]s and [[chemical bond]]ing are the result of [[quantum mechanical]] interactions of [[electron]]s around [[atom]]s. Quantum considerations are also necessary to explain the behaviour of many electronic devices, for instance the [[tunnel diode]].