Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . orma closed circuit and then moved across a magnetic field, acurrent of electricity is produced in the wire ; in other words,if we artificially produce around the wire the magneticwhirls, a current of electricity flows through it when thecircuit is complete. The English physicist, Michael Fara-day, discovered (in 1831) that electric currents could be in-duced in a closed circuit by moving magnets near it, or bymoving the circuit across a magnetic field. Currents thatare so generated
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . orma closed circuit and then moved across a magnetic field, acurrent of electricity is produced in the wire ; in other words,if we artificially produce around the wire the magneticwhirls, a current of electricity flows through it when thecircuit is complete. The English physicist, Michael Fara-day, discovered (in 1831) that electric currents could be in-duced in a closed circuit by moving magnets near it, or bymoving the circuit across a magnetic field. Currents thatare so generated are known as induction currents and thephenomenon termed electromagnetic induction. (Compare withmagnetic induction, ^| 36.) This is a most interesting andvaluable branch of the study of electricity, as upon its prin-ciples is based the operation of many forms of commercialelectrical apparatus, such as dynamos, transformers or in-duction coils, telephones, etc. 277. Currents Induced in a Wire by a Magnet.—Asensitive galvanometer, G, Fig. 260, is removed from the in- 293 294 PRACTICAL ELECTRICITY. ~~\>. Fig. 260.—Current Induced in a Wire by Moving it Past a Magnet. fluence of the bar magnet, NS, and connected by a pieceof copper wire. If a portion of the wire, AB, is quicklymoved down past the pole of the magnet a momentary current isinduced in the wire, causing the galvanometer needle to bedeflected, say to the right of zero, when it will again return to,«:».«:.?.. the zero position. If the ? wire is again moved up past the same poleanother momentary current is in-duced in the wire in the oppositedirection to the former current, asindicated by the momentary deflectionof the galvanometer needle, whichnow swings to the left of zero. Ifthe induced current, then, flows fromA to B on the downward motion itwill flow from B to A on the upwardmotion. If the wire be movedrapidly up and down past the mag-net, the current will alternate indirection with each direction ofmotion,
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