For ordinary currents, this drift velocity is on the order of millimeters per second. Then how come electrical gadgets and stuff respond immediately ?
2007-06-27 02:46:31 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Physics
This is a classic question of electrical engineering and has bothered people for years! The key to understanding what is happening is to realize that the electrons actually do not carry the signal, the field does and the field primarily moves outside the conductor. If the wire is in air, the field sets up at the speed of light in air. So when you flip a light switch to on, the electrons at the light bulb start moving in response to a fiedl that sets up at the speed of light.
If you want more information on this subject, look up information on the Poynting vector. The Poynting vector is a mathematical concept that indicates the direction of power flow. A common example with the Poynting vector is to show that the power along a wire moves with the field outside the wire.
The Wikipedia has a nice discussion of this concept.
2007-06-27 05:12:21 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Electricity travels through the wire as a transverse electromagnetic wave. Just as sound waves travel faster than the air flow that marks its passage, the EM wave travels faster than the electron drift speed. A good analogy is pushing on a rock with a long wooden pole. The rock gets pushed almost as quickly as you push the other end (delayed only by the speed of sound in wood) regardless of how slowly you push..
2007-06-27 23:20:32 · answer #2 · answered by Dr. R 7 · 0⤊ 0⤋
there all stacked up in a wire, as soon as one moves, so do all of them, therefore the response when u switch on a light bulb in instant. Its like a pipe full of water, you could displace the water really slowly, but water will come out of the other end as soon as you displace the water at the first end.
hope that helps.
2007-06-27 09:51:31 · answer #3 · answered by raja 3 · 0⤊ 0⤋
you should think of it more as water. if theres water in a hose, and its flowing out the tap at 3 kilometer per hour. the water already in the hose is also moving at 3km/h
all the water in the hose moves together, putting some mroe in the hose at the tap, will immediately push some out the other end.
2007-06-27 09:50:36 · answer #4 · answered by mrzwink 7 · 0⤊ 0⤋
Most equipment read the magnetic changes and use this to imply the current. The immediate response is because the magnetic change is instant.
2007-06-27 09:50:39 · answer #5 · answered by eric l 6 · 0⤊ 0⤋