induction

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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 .

in·duc·tion / inˈdəkshən/ • n. 1. the action or process of inducting someone to a position or organization: the league's induction into the Baseball Hall of Fame. ∎  [usu. as adj.] a formal introduction to a new job or position: an induction course. ∎  enlistment into military service. 2. the process or action of bringing about or giving rise to something: isolation, starvation, and other forms of stress induction. ∎  Med. the process of bringing on childbirth or abortion by artificial means, typically by the use of drugs. 3. Logic the inference of a general law from particular instances. Often contrasted with deduction. ∎  (induction of) the production of (facts) to prove a general statement. ∎  (also mathematical induction) Math. a means of proving a theorem by showing that if it is true of any particular case, it is true of the next case in a series, and then showing that it is indeed true in one particular case. 4. Physics the production of an electric or magnetic state by the proximity (without contact) of an electrified or magnetized body. See also magnetic induction. ∎  the production of an electric current in a conductor by varying the magnetic field applied to the conductor. 5. the stage of the working cycle of an internal combustion engine in which the fuel mixture is drawn into the cylinders.

induction, inductive The inverse of deduction. Induction begins from particular observations from which empirical generalizations are made. These generalizations then form the basis for theory-building. So-called analytic induction is common in qualitative studies within sociology. This method requires that every case examined in a piece of research substantiates a hypothesis. The researcher formulates a general hypothesis from observation of initial cases; investigates subsequent cases in the search for a negative instance; and reformulates the hypothesis to cope with those confounding cases that are encountered. The process is deemed to be exhausted when no new discrepant cases can be found—a necessarily rather subjective judgement—and the (now revised) generalization is allowed to stand. See also CAUSE.

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.

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 (in-duk-shŏn) n.
1. (in obstetrics) the artificial starting of childbirth, e.g. by injecting oxytocin or puncturing the amnion, when pregnancy has continued considerably beyond the expected date of birth or if there is a risk to the health of mother or infant.

2. (in anaesthetics) initiation of anaesthesia. General anaesthesia is usually induced by intravenous injection of short-acting anaesthetics (such as thiopental).

induction. The final stage in the appointment of a new incumbent. After the priest has been instituted by the bishop, he is inducted to his benefice, usually by the archdeacon, who places his hand on the key of the church door and causes him to toll the bell. The legal effect is to give him possession of the temporalities and control of the parish.

induction
1. (in embryology) The ability of natural stimuli to cause unspecialized embryonic tissue to develop into specialized tissue.

2. (in obstetrics) The initiation of childbirth by artificial means; for example, by injection of the hormone oxytocin.

induction n. enlistment into military service.

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