How Everything Works
How Everything Works How Everything Works

Question 705

How fast does sound travel through the telephone? - T
When your voice travels through the telephone, it doesn't travel as sound. Instead, the microphone of your telephone unit produces an electric current that represents the sound of your voice. From there on until it arrives at the earpiece of your friend's telephone unit, your voice travels as an electromagnetic signal—either an electric current, a radio wave, or a light wave. Only when it reaches the earpiece is the electromagnetic signal used to recreate the sound itself. Since electromagnetic signals travel at or near the speed of light, your voice moves extremely quickly from your telephone unit to your friend's telephone unit. It would be quite easy, for example, for a friend living a few miles away to tell you about a nearby explosion or thunderclap and then have you hear that explosion or thunderclap yourself. Your friend's words would travel much more rapidly through the phone lines than the sound would travel over the countryside.

However, even the speed of light isn't fast enough in some cases. Shortly after the break-up of AT&T, new long-distance carriers began to appear. Some of these companies used geosynchronous satellites to handle the long distance calls. Because these satellites sit about 22,300 miles above the earth's equator, the travel time for radio waves to and from these satellites is a substantial fraction of a second. The delay between when you spoke and when your friend heard your voice was long enough that your friend might have begun talking, too. Those conversations were very awkward because you had to be very deliberate about starting and stopping your speech. You almost had to tell your friend when you were done talking so that they could begin. All modern long-distance calls are handled by surface links so that there is almost no delay, except perhaps when going to the other side of the earth.


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