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Author Topic: Trivia  (Read 663 times)
WH6OC
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« on: July 31, 2004, 12:54:07 AM »

Some Ham Trivia-
What is the typical speed of the current carrying electrons down a copper conductor while conducting a current.  This is of course something that I have read but was also told to me by someone who measures such things.
WH6OC
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WB2WIK
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« Reply #1 on: July 31, 2004, 09:12:13 PM »

Around 297Mmps.
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WH6OC
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« Reply #2 on: August 02, 2004, 01:06:39 AM »

WB2WIK-
297 Mmps-to me that's a strange figure-almost to 299 Mmps plus, the speed of light.  One of Einstein's postulates, paraphrased, says that no object can travel the speed of light and 297 Mmps is pretty darn close.  The way I understand things is that since an electron is an object and has mass, etc., can't even come close to that speed.
WH6OC
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KF4WXD
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« Reply #3 on: August 03, 2004, 10:45:54 AM »

It's not like the electrons have to travel all that far, only over to the next molecule.  Another electron then maks its short hop and so on and so on.  Got that?  Each electron doesn't travel all the way down the wire.

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AA4PB
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« Reply #4 on: August 03, 2004, 06:45:29 PM »

From: http://www.amasci.com/miscon/eleca.html#light

In metals, electric current is a flow of electrons. Many books claim that these electrons flow at the speed of light. This is incorrect. Electrons actually flow quite slowly, at speeds on the order of centimeters per minute. It's the energy in the circuit which flows fast, not the electrons. Metals are always full of movable electrons, and when the electrons at one point in the circuit are pumped, electrons in the entire loop of the circuit are forced to flow, and energy spreads almost instantly throughout the entire circuit. This happens even though the electrons move very slowly.
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I think about it this way: Say you have a long narrow tube filled with ball bearings. You insert another bearing into one end of the tube and almost immediately a bearing drops out of the far end. You think wow, that bearing moved down the tube at the speed of light. But wait - it is a different bearing that dropped out of the far end, not the one you put in. It may take quite a long time of pushing bearings into the tube before the first one you inserted makes it to the far end. The result is almost instantanious but the actual movement of the bearings is rather slow.
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WH6OC
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« Reply #5 on: August 04, 2004, 02:05:56 PM »

I thought it is kind of funny that some would think that current is composed of electrons and is flowing in a circuit with a rate (a coulomb of electrons passing a given point in a circuit in one second equals one ampere) but doesn't have a velocity.  I realize that basic electricity deals with volts, amps, and coulomb, etc., and we get along just fine in solving our day-to-day theory problems without considering this electron flow velocity, with emphasis on basic.  This is not something that is used every day by most people and certainly not required, and...is not a crime if one is not familiar with.  But to simply deny that we have a flow without velocity because one may not know it, I think is odd.  There can be an average velocity of these free electrons in a circuit without getting into just how they get from point A to point B.  Out there somewhere there is probably a list of the unique velocities of the free electron flow for the different elements when subjected to a voltage force. I may try to find it.
And I would not like to think that any reputable author would say that these electrons are traveling at the speed of light, the impulse, at or near.  I have heard of this bearing ball bouncing theory of current flow and in my opinion is just a plain erroneous, over simplification of things.  I think that it is accepted in the scientific world that these free electrons are really moving on so-to-speak down this conductor at a relative high rate of speed when forced by a voltage.  It has not been said that each electon has a constant speed during it's travel down this copper conductor but that each one has this constant average speed.  And this unique speed is independent of the voltage applied.  Whereas of course, the amount of the electrons in the flow is directly porportional to the voltage applied.  And we all know that when this free electon flow gets too large for the conductor the heat of friction just causes the conductor to melt.
Anyway, I put this question under 'trivia' because I think it is as good a place as any.
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AA4PB
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« Reply #6 on: August 04, 2004, 04:22:01 PM »

You are reading too much into the ball bearing thing. It's point is only to demonstrate that it is possible for "energy" to move at a much faster rate than the actual electrons. It is not meant to be an actual description of how electrons flow.
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WH6OC
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« Reply #7 on: August 05, 2004, 12:45:50 PM »

Okay, just let me give you an idea of this speed and clarification.  First of all it is only second hand information, as most information is.  This is the speed I had in mind,'xx,xxx.x kilometers/hour', and the only reason I remember this is that it converts to a relative even number in miles/hour.
In 1958 I was taking an advanced chemistry class in 'Quantum Mechanics' and the instructor brought this topic up in one of his lectures.  I forget the instructor's name but he was a noted chemist and at least on one occasion was a guest speaker for UCLA's chemistry department.  And in passing, he had said that he was part of a three man team working as a research scientist for Dupont that developed teflon in the late 30's. In my opinion he was a top-notch chemist and I have no reason to question him-and I feel fortunate to have had him for this one course.
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AA4PB
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« Reply #8 on: August 05, 2004, 01:58:10 PM »

Here's something else I found at www.newton.dep.anl.gov/askasci/phy99/phy99092.htm . I too can only repeat the information I've gotten from someone else - never measured the speed myself.

Question:  Exactly how fast do electrons travel?
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Answer:  Electrons can have a wide range of speeds.  A slow case: we know that electrons move when there is a current flow in a wire, but the speed at which the electrons themselves move in the wire -- the so-called electron drift velocity -- surprises most people.  For example, for a copper wire of radius 1 mm carrying a steady current of 10 amps, the drift velocity is only about 0.024 cm/sec ! On the fast side: the Bohr model of the hydrogen atom has the (bound) electron zipping around the nucleus at about 2 million meters/sec.  And on the very fast side, some examples are: beta articles, which are emitted by some radioactive materials; and the innermost electrons of atoms of elements having large atomic number, such as uranium.  In these cases the electrons are traveling at very nearly the speed of light. (about 300 million meters/sec).
Rcwinther
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