Self- Induction

(a) A phenomenon of electric currents analogous to the inertia of matter. Just as water which fills a pipe would resist a sudden change in its rate of motion, whether to start from rest, to cease or decrease its motion, so an electric current requires an appreciable time to start and stop. It is produced most strongly in a coiled conductor, especially if a core of iron is contained within it.

As in the case of two parallel wires, one bearing currents which vary, momentary currents are induced in the other wire, so in a single conductor a species of inertia is found which retards and prolongs the current. If a single conductor is twisted into a helix or corresponding shape, its separate turns react one on the other in accordance with the general principles of electromagnetic induction. (See Electro-magnetic Induction) Thus when a current is suddenly formed the coils acting upon each other retard for an instant its passage, producing the effect of a reverse induced current or extra current opposing the principal current. Of course no extra current is perceptible, but only the diminution. When the current is passing regularly and the current is broken, the corresponding action prolongs the current or rather intensifies it for an instant, producing the true extra current. This is current self-induction.

[Transcriber's note: See inductance.]

Synonyms--Electric Inertia--Electro-dynamic Capacity.

(b) A permanent magnet is said to tend to repel its own magnetism, and thus to weaken itself; the tendency is due to magnetic self-induction.