Ask A Scientist© Engineering Archive

Index Key:   ENG051
Author:      mike b caciari
Subject:     Speed electricity travels.
How fast does the electrical current travel?

Response #:  1 of 2
Author:      david r munoz
This is an interesting question.  I wish that I knew the answer.  My first
thought is that it travels at near the speed of light but light travels
slower within our atmosphere than it does in a vacuum, so I am wondering if
the medium through which the electricity\pass passes makes a difference.

Current represents the charge per unit time that flows in a conductor what
we would need with the this value is the charge capacity per unit length of
the conductor.  I am sure that it would depend on the resistivity.

This would be a very good question for the Physics section.  Unfortunately,
I do not believe that there is an electrical engineer that answers questions
on this section of NEWTON and my background is in Mechanical but I am sure
that the physicists would be happy to help.

Response #:  2 of 2
Author:      proach
There are two aspects to this question:  how fast does an electrical signal
travel, or how fast do the current carriers travel?  Dr. Dave is correct
that the signal travels at the speed of light.  This is somewhat slower in a
metal wire than it is in vacuum.  But the actual charge carriers (electrons
if it is a metal) move much slower.  This is determined by their interac-
tions with the metal atoms.  It is measured by a quantity called mobility.