| dbo:abstract |
Electromagnetism is one of the 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 currents give rise to magnetism. Michael Faraday discovered the converse, that magnetism could 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 waves 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 waves 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 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 charges so magnetic fields do not arise and are not considered. Permanent magnets can be described without reference to electricity or electromagnetism. Circuit theory deals with electrical networks where the fields are largely confined around current carrying 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 reactions and chemical bonding are the result of quantum mechanical interactions of electrons around atoms. Quantum considerations are also necessary to explain the behaviour of many electronic devices, for instance the tunnel diode. (en) |
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If there is no charge enclosed by a closed surface, then the amount of electric field flowing into it must exactly cancel with the electric field flowing out of it. (en) Because the flow of magnetic field out of a closed surface must cancel with the flow into it, magnets must have both North and South poles which cannot be separated into monopoles. (en) The electron's rest frame (en) The lab frame (en) Kirchoff's junction rule : I1 + I2 + I3 = I4 + I5 Kirchoff's loop rule : V1 + V2 + V3 + V4 = 0 (en) |
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The right-hand grip rule for a straight wire and for a coiled wire . Electrical current passed through a wire coiled around an iron core can produce an electromagnet. (en) The force exerted on a positive charge by an electric field and a magnetic field combine to give the Lorentz force. (en) |
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Coil right-hand rule.svg (en) GaussLaw2.svg (en) KVL.png (en) Manoderecha.svg (en) Pierwsze prawo Kirchhoffa.svg (en) Relativistic electromagnetism fig5.svg (en) Relativistic electromagnetism fig6.svg (en) VFPt Earths Magnetic Field Confusion.svg (en) Openstax college-physics 22.17 Lorentz-force-right-hand.jpg (en) Force of an electric field on a positive charge.png (en) |
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Electromagnetism is one of the 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 currents give rise to magnetism. Michael Faraday discovered the converse, that magnetism could 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 waves 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 waves differ from light only in that the wavelength of the for (en) |
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Introduction to electromagnetism (en) |
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