The voltage difference between the tip and ring lines of the phone line when it is on-hook is
A) 0V
B) 90V rms
C) 2V rms
D) 48 VDC
E) 2 mV rms

Question

Quizplus · Accepted Answer

The voltage difference between the tip and ring lines of a phone line when it is on-hook (not in use) is typically around 48 VDC (volts direct current). This voltage is used to detect when the phone goes off-hook (picked up) as the circuit is completed and current starts to flow, signaling the exchange to provide a dial tone or take other actions.

The Voltage Difference Between the Tip and Ring Lines of the Phone