Self-Induction


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self-induction

[¦self in¦dək·shən]
(electromagnetism)
The production of a voltage in a circuit by a varying current in that same circuit.

Self-Induction

 

the appearance of an electromotive force (emf) of induction in a conducting circuit when the current in the circuit changes. This phenomenon is a special case of electromagnetic induction. The current change in the circuit causes a change in the magnetic flux through the surface enclosed by the circuit. As a result, an emf—the emf of self-induction—is induced in the circuit. The direction of the emf is determined by Lenz’s law: if the current in the circuit increases, the emf of self-induction opposes this increase; if the current decreases, the emf opposes the decrease. Thus, self-induction is similar to the phenomenon of inertia in mechanics. The emf of self-induction eL is proportional to the rate of change of the current i and to the self-inductance L of the circuit: eL = - Ldi/dt.

Because of self-induction, the closing of an electric circuit containing a constant emf does not instantaneously establish a steady current; the current is established only after a certain time interval (see TRANSIENT). Similarly, when the circuit is opened, the current flow does not cease instantaneously. The emf of self-induction that is induced by the opening of the circuit can be several times greater than the emf of the source. In AC circuits, the emf of self-induction causes the current in an inductance coil to lag in phase behind the voltage across the ends of the coil by (see ALTERNATING CURRENT).

The phenomenon of self-induction plays an important role in electrical engineering and radio engineering. Self-induction causes the recharging of a capacitor connected in series with an inductance coil (see OSCILLATORY CIRCUIT); as a result, natural electromagnetic oscillations are established in the circuit.

REFERENCE

Kalashnikov, S. G. Elektrichestvo. Moscow, 1970. (Obshchii kurs fiziki, vol. 2.)

G. IA. MIAKISHEV

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