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Why is conversation across continents instantaneous using telephone?

  1. Jan 14, 2014 #1
    For my question let us just consider two telephone (POTS) connected by wire, junction boxes, several telephone switches/exchanges etc without any wireless connection. One telephone is in continent A and other is in continent B. I understand how sound is converted into electric current by a microphone in a telephone and how a speaker reverses the process of electric current to sound on far end. What I am still confused is how electric current from one telephone reaches the far end telephone instantaneously.

    1) Does the electron travel from one telephone to other that fast? or
    2) Does energy from electron travel from one telephone to the other? or
    3) Is it due to transfer of ElectroMagnetic energy due to electric current? Does electromagnetic wave go along the telephone wire and junction box and through the telephone switches?
    4) is it something else?

    I would appreciate if someone can help me understand the theory behind it.
  2. jcsd
  3. Jan 14, 2014 #2


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    Staff: Mentor

    Welcome to the PF.

    It is not "instantaneous". At best, it is at about half the speed of light, along the shortest possible path.

    When using satellites to make the cross-ocean hop, the delay is quite easily noticed. When using undersea fiber optic cables, the delay is harder to hear.
  4. Jan 15, 2014 #3


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    No. In fact, the electrons in the wires in your phone do not even make it to the other phone. If you take the common analogy of water flowing through a pipe, it would be similar to the water moving only a few feet along a 1,000 mile long pipe.

    Energy does travel from one phone to the other, but it is not "electron" energy. It is simply electrical energy in the formal of voltage and current.

    Yes, but it isn't a straight shot from one phone to the other. The devices in between the two phones commonly have their own circuits and will detect and amplify the voltage/current changes coming in from each phone before sending them out again.
  5. Jan 15, 2014 #4


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    It doesn't reach the far end instaneously. Voice telephone signals move at about 100,000 kilometers per second or thereabouts; that's very fast but there's still a bit of a delay. You won't notice a delay smaller than a few tenths of a second, but it's still there.

    (As an aside, it's not the current that's traveling, it's the voltage. We're using electrical forces to communicate the same way that you and I could communicate if we held opposite ends of a long pole; if I twist or tug my end you'll feel the force, so we can send signals even though the pole isn't moving).
  6. Jan 15, 2014 #5

    I learned my electrical theory back in 1959 and it still holds good today. The analogy I was given for the transmission of electrical impulses over a cable was a Newton's Cradle. dropping a ball at one end resulted in energy being transferred through the other balls to push the other end ball out. Much like a long pipe full of balls, pushing another in one end will push one out the other end, almost instantaneously, irrespective of the length of the pipe. (if the pipe had no balls in it, it wouldn't be a 'conductor').
    Last edited: Jan 15, 2014
  7. Jan 15, 2014 #6


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    Nothing is "instantaneous". The speed of light imposes a delay, even between the components inside an atom.
  8. Jan 15, 2014 #7
    Thanks to everyone for replying back to my question.
    It is now clear that there is some delay even though as human that delay is not perceivable and may seem instantaneous.
    It is also clear that electron from one telephone doesn't travel from one telephone to another but the disturbance or signal is transferred from one end to another. Analogy of water flowing through pipe, tugging of long pole and pushing of ball across a pipe full of balls were very helpful.

    However, I am still not clear about how exactly is signal transferred so fast. Assuming that entire connection end to end consists of various sections of metal conductor only (junction box, telephone exchanges, tandem, gateway, drop wire etc) and there is no fiber or wireless or satellite involved? Does electromagnetic play any role in transfer of signal or is it due to free electrons in metal conductor?
  9. Jan 15, 2014 #8


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    Electrons in a wire are not like the little balls in a newtons cradle. They don't sit right up next to each other waiting for something to hit them. They are constantly moving in all directions through the wire, and the application of a voltage causes their random motions to have a net movement in a certain direction. When you first apply a voltage it moves down the wire as the charges react, and even though each individual charge may only have its direction and velocity changed very little, the effects adds up and the change in voltage moves down the wire at a very high speed. And this doesn't even take into account things like transformers, inductors, etc.
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