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Q & A: Why do electrical signals travel fast?

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Most recent answer: 03/08/2014
Q:
the speed of electron in copper wire is 1mm/s then as soon as we switch on of a bulb then bulb blinks quickly....that is so,,,fast like speed of light...it's shows property of light ......can anybody explain why did this happens???????????????
- tabish (age 18)
A:

Before answering your question, let me comment on one side issue. I'm not sure where you get the 1 mm/s speed from. The important current-carrying electrons travel, in all different directions, at the Fermi speed, which is ~ 1.6*108 cm/s in copper. That's still under 1% of c, but it's pretty fast. Perhaps the 1 mm/s was the average velocity when there's some small density of current flowing.

Meanwhile, yes the signal does travel at almost the speed of light, faster even than the Fermi speed. The reason is that electrons don't have to travel all the way from the switch to the light. There are already electrons in all the wires, including the light. All that's needed is for each to give a push to it's neighbors to start them moving. The electrical fields that carry the force from one electron to another propagate at the speed of electromagnetic waves, and light is an example of an electromagnetic wave.

Think of what happens if you send a signal by pushing and pulling on a stick. The other end of the stick responds very quickly to whatever you do. Your end doesn't have to travel all the way down to the other place.

Mike W.


(published on 03/08/2014)

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