speed of electrons

[charlie b]

Re: speed of electrons

Very true Ed. Here's why:

Current is created within a capacitor by an attempt (on the part of the outside world) to change its applied voltage. In other words, the change in current happens RIGHT AWAY (in the manner I?ve described above), whenever the voltage BEGINS to change (i.e., before the voltage reaches its new value). That is why current leads voltage in a capacitor. The mathematical version of this statement is I = C (dV/dt). The ?dV? means a change (?d? for difference) in voltage, the ?dt? means per unit of time.

By contrast, an inductor will resist any change in current, by creating an internal voltage of opposite polarity. In other words, the change in voltage happens RIGHT AWAY whenever the current BEGINS to change (i.e., before the current reaches its new value). That is why current lags voltage in an inductor. The mathematical version of this statement is V = L (dI/dt). The ?dI? means a change in current, the ?dt? means per unit of time.

An AC voltage is always changing, so a capacitor?s current is always changing, but earlier in time (i.e., ?leading? the voltage). Similarly, AC current is always changing, so an inductor?s voltage is always changing, but earlier in time (i.e., current changes occur later in time - ?lagging? the voltage).

 

[physis]

Re: speed of electrons

Boy, I wish I had my old physics books here, but I don't.

My recollection is that DC current in an average copper conductor is on the order of 95 percent the speed of light. 300,000,000 meters/second X .95. Not transference of energy from one tennis ball to another but one tennis ball being isolated and clocked.

AC vibrates back and forth (same speed, less distance).

When you increase the voltage what you get is more turbulance in the conductor. Less electrons moving in a straight line more electrons crashing into each other and the conducter boundries.

this converts some of the I and E into heat. But I don't think that it reduces the velocity of the electrons.

Even the ones moving at a tangent to the direction of the coductor are still travelling at the same velocity as those moving in a perfectly straight line!

 

[al hildenbrand]

Re: speed of electrons

This has been an interesting discussion. Frank, did it help?

For myself, my understanding of electrical phenomena has grown a little at a time as I have come to understand, first, the DC model, then the mathematics of AC, and lastly, the quantum physics model. I have found that much of the mathematics of AC turn AC into a DC model, with tricks for clearer understanding of transients, phase shift and harmonics. However, working as an electrician, modern physics hasn't offered any real help, but modern physics has made for very interesting conversation and has enrichened my spiritual life

 

[physis]

Re: speed of electrons

I'm going to try to redeem myself from my last post on this topic.

I'm going by memory and using some arbitrary values. You can just replace any bad numbers with good ones and this approach should be pretty close to reality. There are so many posts I haven't read them all, if someone all ready took this route I'm sorry for being redundant.

A coulomb is the number of electrons that pass a point in one second at one amp. I think that it's 6.18 x 10 to the 24th. (memory?)

Consider 1 amp through a 1 mm diameter conductor.

It's cross sectional area is 7.854 x 10 to the -7th sq. meter.

Using a fictional conductor atom of 1 trillionth of a meter diameter sphere it's cross sectional area if cut through the center is 7.854 x 10 to the -25th sq. meter.

Ignoring the geometry of the atomic bonding and considering one layer of atoms on a flat surface with no space between them, a cross section of the conductor would contain 10 to the 18th atoms.
7.854 x 10 to the -7th / 7.854 x 10 to

the -25th = 10 to the 18th.

So you can get a stream of electrons 10 to the 18th wide through the conductor. At 1 amp 1 coulomb(or 6.18 x 10 to the 24th electrons) pass a point in one second. 6.18 x 10 to the 24th / 10 to the 18 = 6,180,000. That's how many layers of atoms the electrons passed through in one second.

Being as how atoms aren't cubes 3 layers of atoms would be closer to 2 atom diameters wide instead of 3. So 6,180,000 x 10 to the -12th (the atom diameter) x 2/3 = 4.12 x 10 to the -6th meter or 4.12 thousandths of a milimeter per second or 14.832 milimeters an hour.

If you double the voltage you also double the current. At 2 amps twice the electrons pass a point in a second and in order to do that they have to go twice as fast. Assuming I'm not making a mistake somewhere it looks like without resistance high enough to limit current and without heating wires and changing resistance:

Electron velocity is directly proportional to the voltage.

 

[al hildenbrand]

Re: speed of electrons

Hey Physis,

No redemption is necessary.

The IEEE Standard Dictionary of Electrical and Electronic Terms defines "coulomb" as (in its entirety):

The unit of electric charge in SI units (International System of Units). The coulomb is the quantity of electric charge that passes any cross section of a conductor in one second when the current is maintained constant at one ampere.

I added the emphasis on electric charge. Take a look at Ed MacLaren's posts and diagram with the idea in mind that a positive charge (the absense of an electron) is also current.

I think it is important to remember how alien the sub nuclear world is. Charlie B lays out a great sense of the size of a proton and an electron and the distance between them in terms that we can measure against the length of our bodies. Looking at Charlie B's hypothetical electron the size of a grain of salt (which is the last post on the page linked to), what one would see would be very alien compared to what we think of as a grain of salt. My mind sees a grain of salt as cubical with hard faces and corners.

An electron is more a locus of vibration, of waves, that exhibit mass. The edges of the locus are not sharp, rather they blur off, thin out, as it were, but never diminish to zero. The vibrational locus of a salt grain sized electron (the outer shell electron of a copper wire atom) will respond to the absence of an electron in another copper atom over 15 miles away because of the "electric" nuclear force.

This boggles my mind! Two tiny specks of matter that far apart tugging and pushing on each other across a void! And, all the while, these specks are flying about their home atoms at near light speed. And when one electron hops from one atom to the next it does so at the same speed.

The speed of the electron doen't change. . .rather, the frequency of the hops per unit time increases as the coulombs passing a given point increases.

 

[bphgravity]

Re: speed of electrons

It has been estimated that if two grams (0.070 ounces) of electrons could be collected into two equal spheres and these spheres were a distance of o.39" apart, they would repel each other with the force of 320,000,000,000,000,000,000,000 tons. A force greater than the weight of the water in all oceans of the world!!!!

 

[iwire]

Re: speed of electrons

Now that's some power! now if I can only figure out how to get the brakes to hold me at the line...

 

[physis]

Re: speed of electrons

Yep, your right Al, it's a charge. I found a book here that's got the value of a coulomb. My model's got two errors.

[1] A coulomb is an amount of charge equal to that of 6.25 x 10 to the 18th electrons. It's not a quantity of electrons as I had posted.

[2] My recolection of the quantity was wrong, it's not 6.18 x 10 to the 24th.

So if you correct my numbers you would come up with the rate of charge moving through the conductor and that's not necessarily the rate of electrons. But if it's not, what's carrying the charge?

I don' have all the books on this stuff that I used to, this one I'm looking at is ignoring the existance of electrons in a conductor.

 

[al hildenbrand]

Re: speed of electrons

Physis,

Each copper atom that is minus an electron "carries" the charge. The instant that an electron takes off towards the neighboring atom to fill the absense there, it creates an absense at its first atom. The positive charge, the "hole" hops.

 

[jxofaltrds]

Re: speed of electrons

Physis

This is from The Battelle Memorial Institute.

Electron (-1.6 X 10 (-19)C)
Proton (+1.6 X 10(-19)C)

If this is incorrect please let me know and I will forward it to the publisher.

PS This is outside of my understanding, I just remember where I read it.

Mike P.

 

[physis]

Re: speed of electrons

That's right Mike, it's the reciprocal of a coulomb. If you divide 1 (coulomb) by the number of the electrons charges it represents (it's already posted above) your left with the charge that one electron has (the number you posted).

Al:
Of course protons or electrons without there opposite counterparts to cancel each other have a net charge. And the motion of the charge, or it's hopping as you say, is still due to the electron moving. I really don't know if the charge moving is related solely to the electrons moving or if there are other phenomena involved but if the former is true then I think my approach should work and voltage would increase speed. I would think the charge has to follow the electrons (or positive holes).


Sam

[ May 05, 2003, 02:20 AM: Message edited by: physis ]

 

[charlie b]

Re: speed of electrons

Originally posted by physis:At 2 amps twice the electrons pass a point in a second and in order to do that they have to go twice as fast. ? Electron velocity is directly proportional to the voltage.

They don?t have to go faster. In fact, velocity is constant (i.e., it is independent of voltage). Try looking at it this way. Stand on a bridge over a major highway. Let?s presume (for this discussion) that every car is going exactly 60 miles per hour. Using a stopwatch to count off one minute intervals, count cars as they pass by underneath you. Suppose that the first time you do this, you have counted 5 cars. Lets define 1 ampere as ?5 cars per minute.? Come back later and try again. Suppose this time you count 15 cars, each and every one moving a the same 60 mph. The current is now 3 amps, since 3 times more cars have passed under the bridge then you saw the first time. It?s not the cars? speed that has changed, it is the number that have passed by the point in space at which the measurement (i.e., the counting) takes place.

 

[physis]

Re: speed of electrons

I'm assuming all the lanes to be full and a number of cars passing to be manditory. It may be that this is the point where the wire melts.

It occurs to me that there's two different ways to look at speed. One is how fast an electron changes atoms, and that's probably constant. And the other is how far a hand full of electrons go in an hour, which I think would be an average.

I may just be wasting post space. Looking at it as how many electrons can fit through the conductor may simply be wrong.

[ May 05, 2003, 03:28 PM: Message edited by: physis ]

 

[charlie b]

Re: speed of electrons

Originally posted by physis: I'm assuming all the lanes to be full and a number of cars passing to be mandatory.

You?re getting closer to seeing the picture. But under this analogy, you would have to imagine a bridge over 100,000 lanes of traffic, and expect to count cars on the order of fewer than ten per minute. The drivers will probably never see each other, since they are spaced miles apart. The lanes are not full, not by a long shot. As viewed from the size perspective of an electron, the surrounding space is just that: space, empty space.

It occurs to me that there's two different ways to look at speed. One is how fast an electron changes atoms, and that's probably constant. And the other is how far a hand full of electrons go in an hour, which I think would be an average.

The two speed numbers are the same, and are just shy of the speed of light. Let?s ignore the fact that any one electron that jumps from one atom to the next might not continue on to the third atom in line. It may get trapped in the second atom, and some different electron might jump from atom #2 to atom #3. Let?s ignore that. Let?s presume that we can?t tell which electron is which, but that we can count them very quickly and very accurately. All we will see, as we stand at one point along a wire, is some number of electrons speeding by us. Every single electron moves past our position at nearly the speed of light. If the number that pass in one second happens to be 6.25 x 10 to the 18th, then the current is one amp. If the number is 100 times more than that (i.e., 6.25 x 10 to the 20th), then the current is 100 amps.

Looking at it as how many electrons can fit through the conductor may simply be wrong.

As I said, all the electron sees is a vast, great, open, empty space. You could pass as much current through a wire as you wish; the wire would melt long, long, long before the electrons would have run out of room to move.

 

[physis]

Re: speed of electrons

You just don't want to let me push electrons through wires as fast as I want to.

Ok, I see what your saying, it doesn't matter how many electrons will fit.

And the guy caught in traffic behind the bridge yelling obsenities out the window doesn't make the cars on the bridge go any faster.

 

[jtb]

Re: speed of electrons

Yes, electrons move at the same speed regardless of the voltage input. More of them move, however.

Electrons move at different speeds in different materials. This speed is called drift velocity.

Also, at a high enough voltage (or current) the electrical characteristics of the medium can change, thus the speed. Think of temperature and dielectric breakdown effects.

 

[jtb]

Re: speed of electrons

OK now. Given the fact that Positrons have less mass than Electrons, how fast can they travel, and do they leave negative holes? Which way is current defined? What about a Tachyon's minimum speed? Charge? Current? LOL

 

[sparkmantoo]

Re: speed of electrons

i can tell you exactly how fast they move.....fast. is this something that has to do with the nec, and if it does i don't see that article. where is it? some of us need to get out of the house more.

 

[ronaldrc]

Re: speed of electrons

Back to the speed of electricity in a conductor.

Please for ones just getting into this field please ignore this post.

Learn and study in accordance with your instructor.

I like the water analogy of electricity flowing through a pipe system better than any theory we use. No one knows the speed I don?t think.

Personally I?m weak in the math dept. but the person gifted in this area can use this analogy and the math together can solve about any electrical problem good enough to apply it to the practical world.

The problem I have with the whole mess is not the speed ,but rather the electricity really flows completely around the entire loop or circuit or not?

This is just another idea .

Imagine a water hose and instead of water imagine balls the same diameter as the hose lined end to end and touching and this is the particles we call electrons.

If you push it first ball even an 1/2 inch the last ball will move 1/2?. in other words we don?t know that the electrons make a full trip around the loop or not?

Maybe how far they move is dependent upon what the amplitude of the voltage is.

Lets say 1 volt will push them through the conductor 1/2? and 3 volts would push them
3/4? and the energy that produces this action is in spurts and in between spurts the electrons come right back to there original position from where they started.

And this oscillation is the energy we call electricity.Like Bennie says all this energy can
do is produce heat and magnetism and anyway you look at it, it is very simple we just
can?t see it.

We can still rationalize DC from AC the DC is just pushing into the same electrode or same side of the circuit all the time and AC pushes into one electrode or in one side of the circuit once and then changes and pushes in the direction of the other electrode of other side of the circuit next time.

And these pulse or spurts of energy are so fast we can?t measure them and in the DC form they seem as a steady flow.

Just a thought.

Ronald :roll:

 

[physis]

Re: speed of electrons

Thank you for bringing to my attention that Bennie said electricity can only make heat and magnetism. When he reads this it will be because electricity is making photons.

[ May 12, 2003, 04:38 AM: Message edited by: physis ]