what is the velocity of the telephone signals?

Answer 1

The velocity of telephone signals is the velocity of light in the medium, close to c, about a foot per nanosecond.

The electromagnetic wave that the telephone creates propagates with the speed of light and carries the information that you transmit.

The actual electrons move a whole lot slower than that. But the effect of the em wave is felt very quickly at the other end of the line.

you can easily confirm this in the lab, by the way, with an oscilloscope and a pulse generator. Send a pulse down an unterminated cable and watch for its reflection to come back to the source. It takes roughtly twice (to and fro) the distance (in feet) in nanoseconds.

Across the United States it takes roughtly 16 ms for talk to get to LA from NY if land lines are used (repeaters add a bit more delay).

Answer 2

Telephone signals can travel a number of ways.

The velocity of a signal down a metal wire depends on the physical nature and construction of the wire. For most common wires, it is somewhere between 50% and 90% of the speed of light in a vacuum.

The velocity of light in a fiber optic cable depends on its refractive index, and is about 65% of the speed of light in a vacuum.

The velocity of a terrestrial microwave transmission through air is very very close to 100% of the speed of light in a vacuum. The velocity of a satellite transmission is 100% of the speed of light in a vacuum.

Answer 3

Right answer; wrong reason: electrons actually travel rather slowly. Turning on your ceiling light would take several minutes if the electrons had to wander from the switch to the fixture. Just like water molecules don't depart much from their equilibrium position to propagate surface waves. Or take "the wave" at sporting events, each crest of which propagates around the stadium in a few seconds, though none of the fans actually moves in the direction of propagation.

Same thing for telephone signals - or any other kind of electrical or radio signals. Being made of the same stuff as light, they propagate at the same speed. However, telephone cables are encased in insulation, which slows them down in much the same way that light slows down when it propagates through glass or water. When the insulation on the wires is polyethylene, the signals do travel at about 2/3 the speed of light. This can vary slightly, depending on what the insulation is. The speed can vary somewhat with the frequency of the signal as well, with audio signals propagating somewhat slower than signals on a radio-frequency carrier.

The speed of propagation is given by the formula

Im (√[(R + jωL)(G + jωC)])

where Im (x) is the imaginary component of x,
j = √(-1),
ω is the angular frequency of the signal, which is 2π times the frequency,

R is the series resistance per unit length, which varies with the gauge of the wire used in the cable and with the frequency, increasing at high frequencies because of the skin effect,
L is the series inductance per unit length of the cable, which is somewhat frequency-dependent and takes on one of two values with a transition region, depending on how well-developed the skin effect is at that particular frequency and takes on a value of about 0.62 millihenries per km,
C is the parallel capacitance per unit length of the cable, which is 0.052 microfarads per km,
and G is the mutual conductance per unit length of cable, which is usually negligible for polyethylene cable.

R, L, C, and G are measured at the frequency of interest. These parameters are also measured between the conductors at one end of the cable with the other end shorted for R and L measurements and open for C and G measurements. In practice, these measurements are only taken at audio frequencies; at carrier frequencies, measuring the speed of propagation directly is easier.

At audio frequencies, the effects of R and C predominate; at carrier frequencies, L and C do despite the increase in R with frequency.

Answer 4

I'm pretty sure telephone signals travel at about 2/3 of the speed of light, because 2/3 the speed of light is the velocity in which electrons travel.

Answer 5

It depends on the transmission line characteristics of the twisted-pair of wires that constitute the telephone line (shunt capacitance per unit length, series inductance per unit length, and series resistance per unit length).

Most telephone line twisted pairs from your house to the local switching office have characteristics that give a propagation velocity in the neighborhood of between 0.57c and 0.59c.

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Answer 6

The speed of a charged particle in copper is very slow: about 0.01 cm/s.
At this rate, it takes about 3 hours for a charge to travel about one
meter. The electric field (signal) travels at the speed of light through
copper. The charge is not carrying the information, per se, but the
information is transmitted by the electric field. It is like a molecule of
water does not travel across the ocean, but the wave does.