induction

induction in electricity and magnetism, common name for three distinct phenomena. Electromagnetic induction is the production of an electromotive force (emf) in a conductor as a result of a changing magnetic field about the conductor and is the most important of the three phenomena. It was discovered in 1831 by Michael Faraday and independently by Joseph Henry. Variation in the field around a conductor may be produced by relative motion between the conductor and the source of the magnetic field, as in an electric generator , or by varying the strength of the entire field, so that the field around the conductor is also changing. Since a magnetic field is produced around a current-carrying conductor, such a field can be changed by changing the current. Thus, if the conductor in which an emf is to be induced is part of an electric circuit, the induction can be caused by changing the current in that circuit; this is called self-induction. The induced emf is always such that it opposes the change that gives rise to it, according to Lenz's law . Changing the current in a given circuit can also induce an emf in another, nearby circuit unconnected with the original circuit; this type of electromagnetic induction, called mutual induction, is the basis of the transformer . Electrostatic induction is the production of an unbalanced electric charge on an uncharged metallic body as a result of a charged body being brought near it without touching it. If the charged body is positively charged, electrons in the uncharged body will be attracted toward it; if the opposite end of the body is then grounded, electrons will flow onto it to replace those drawn to the other end, the body thus acquiring a negative charge after the ground connection is broken. A similar procedure can be used to produce a positive charge on the uncharged body when a negatively charged body is brought near it. See electricity . Magnetic induction is the production of a magnetic field in a piece of unmagnetized iron or other ferromagnetic substance when a magnet is brought near it. The magnet causes the individual particles of the iron, which act like tiny magnets, to line up so that the sample as a whole becomes magnetized. Most of this induced magnetism is lost when the magnet causing it is taken away. See magnetism .

induction In physics, process by which magnification or electrification is produced in an object. In electromagnetic induction, an electric current is produced in a conductor when placed within a varying magnetic field. The magnitude of the current is proportional to the rate of change of magnetic flux. In a transformer, the alternating current in the primary coil creates a changing magnetic field that induces a current in the secondary coil. See also Faraday's laws; inductance

induction The creation of a voltage by changing the magnetic flux such that the amount of voltage induced is directly proportional to the rate of change of the magnetic flux according to Faraday's or Neumann's law (see also LENZ'S LAW). In applied geophysics, induction is a fundamental process in electromagnetic (EM) prospecting; a primary EM field is used to induce a secondary field in any subsurface conductors and the resultant of the two fields is measured. The strength of the secondary field, which is a direct function of the electrical conductivity of the ground, can then be determined.