A changing magnetic field induces an electromotive force emf and, hence, an electric field. The direction of the emf opposes the change.
The electric field from a changing magnetic field has field lines that form closed loops, without any beginning or end. Magnetic fields are generated by moving charges or by changing electric fields.
The symmetry that Maxwell introduced into his mathematical framework may not be immediately apparent. The displacement current introduced by Maxwell results instead from a changing electric field and accounts for a changing electric field producing a magnetic field.
The equations for the effects of both changing electric fields and changing magnetic fields differ in form only where the absence of magnetic monopoles leads to missing terms. This symmetry between the effects of changing magnetic and electric fields is essential in explaining the nature of electromagnetic waves.
The electromagnetic force and weak nuclear force are similarly unified as the electroweak force. This unification of forces has been one motivation for attempts to unify all of the four basic forces in nature—the gravitational, electrical, strong, and weak nuclear forces see Particle Physics and Cosmology. We then have a self-continuing process that leads to the creation of time-varying electric and magnetic fields in regions farther and farther away from O.
This process may be visualized as the propagation of an electromagnetic wave through space.enter
magnetism: Evolution of Electromagnetic Theory
In , Thomas Young — showed that when a light beam was separated by two narrow slits and then recombined, a pattern made up of bright and dark fringes was formed on a screen. Young explained this behavior by assuming that light was composed of waves that added constructively at some points and destructively at others see Interference.
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Subsequently, Jean Foucault — , with measurements of the speed of light in various media, and Augustin Fresnel — , with detailed experiments involving interference and diffraction of light, provided further conclusive evidence that light was a wave. So, light was known to be a wave, and Maxwell had predicted the existence of electromagnetic waves that traveled at the speed of light.
These fields are fundamental in nature and can exist in space far from the charge or current that generated them. Remarkably, electric fields can produce magnetic fields and vice versa, independent of any external charge. A changing magnetic field produces an electric field , as the English physicist Michael Faraday discovered in work that forms the basis of electric power generation.
Conversely, a changing electric field produces a magnetic field, as the Scottish physicist James Clerk Maxwell deduced. The mathematical equations formulated by Maxwell incorporated light and wave phenomena into electromagnetism. He showed that electric and magnetic fields travel together through space as waves of electromagnetic radiation , with the changing fields mutually sustaining each other.
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Examples of electromagnetic waves traveling through space independent of matter are radio and television waves, microwaves , infrared rays , visible light , ultraviolet light , X-rays , and gamma rays. All of these waves travel at the same speed—namely, the velocity of light roughly , kilometres, or , miles, per second. They differ from each other only in the frequency at which their electric and magnetic fields oscillate. The interpretation of his work, however, was broadened in the 20th century.
During the late s, physicists discovered that other forces in nature have fields with a mathematical structure similar to that of the electromagnetic field.
History of electromagnetic theory - Wikipedia
These other forces are the strong force , responsible for the energy released in nuclear fusion , and the weak force , observed in the radioactive decay of unstable atomic nuclei. In particular, the weak and electromagnetic forces have been combined into a common force called the electroweak force. The goal of many physicists to unite all of the fundamental forces, including gravity, into one grand unified theory has not been attained to date. An important aspect of electromagnetism is the science of electricity, which is concerned with the behaviour of aggregates of charge, including the distribution of charge within matter and the motion of charge from place to place.
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