The Telephone
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-418
2025-12-15
30
is an instrument used for the purpose of transmitting speech to a distance. The receiver of the Bell telephone is shown in section in Fig 1. M is horseshoe magnet, around each pole of which a coil of fine wire is fixed. In front of the poles of the magnet a thin disk of iron D is fixed by its edge.
Wires leading from the coils through the handle are fastened to binding posts P.
When a current of electricity passes through the coils, it will change the number of lines of force going out from the poles of the magnet, and either increase or decrease the attraction the magnet has for the disk. If at the transmitting end of the line a person speaks into a similar instrument, the rarefactions and condensations of air produced by the voice will cause the disk to vibrate, thus making rapid changes in the distance of the disk from the end of the magnet, and these will induce currents in the coils. These currents coming to the receiver end, and passing through its coils, will set up similar vibrations in its iron disk, which will set up rarefactions and condensations in the air and thus reproduce the original sounds.
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