Telephone Line Circuit
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-419
2025-12-15
30
One of the many ways in which a subscriber's instrument is coupled with a telephone line is shown in Fig. 1.When the subscriber's receiver R is on the hook the current from B passes through an inductive resistance a, the line L', the storage battery D, the call bell C, the line L, the central station lamp, and the inductive resistance b, to the other side of the battery B. Since the resistance of the call bell is about 1000 ohms, the current is not enough to light the lamp. When, however, the receiver is taken from the hook, the secondary S of the induction coil, and the receiver in series with it, is put in parallel with the call bell. As this parallel circuit has a resistance of less than 50 ohms, the current is sufficient to light the lamp at central, signaling for the line. The slight current passing from B through the storage cells at D while the receiver is on the hook is sufficient to keep D fully charged, ready to send its current through the local circuit when the receiver is off the hook. The transmitter T is shown in series with the primary P of the induction coil.
Central calls the subscriber by closing the jack and cutting out the lamp, when the current will be large enough to ring the bell C.
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