MadSci Network: Engineering |
The speed of electricity through a wire is a bit of a complex question. It depends on whether you are considering the rate at which electrons themselves flow along a wire or whether you are considering the rate at which an electrical signal passes along a wire. In the first case, electrons themselves move quite slowly - about 100 micrometres per second (or, from another perspective, 1 metre in about 2.8 hours!) Clearly, this is not what we observe when we turn on a light switch. Ideally, electricity moves at the speed of light. Imagine a tube full of marbles. If you push a marble in at one end of the tube, another marble pops out the other end almost instantaneously. Even if the individual marbles are moving very slowly, the marble "wavefront" is travelling at a very high velocity. In the real world, things are not quite so tidy. Electricity flowing through a gas, or having to work its way through electronic components such as resistors or capacitors, can be slowed to speeds of 60 to 80 percent of light speed. However, that's still fast enough that you can safely expect the light to come on as soon as you flick the switch. See this site for more detailed information: http://www.itwlinx.com/protection_reference.htm
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