Speed of free electrons in vacuum, plasma and superconductors?

In summary, the speed of free electrons in vacuum, plasma and superconductors is not a set speed and is based on its total energy. It is possible to slow down electrons using magnetic fields, as seen in the Penning trap experiment. However, even in low temperature superconductors, electrons still have some velocity due to the uncertainty principle. The minimum linear speed observed for electrons is the Fermi velocity, but it is a probability distribution. Experiments have been conducted to measure electron velocities in superconductors and plasma, with a focus on drift velocity. It is possible to slow down electron beams, but they will still have some velocity due to the nature of electrons.
  • #1
marion.s
12
0
What is the speed of free electrons in vacuum, plasma and superconductors?

Can we 'slow down' free electrons? Just how slow can we make electrons go?
 
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  • #2
The speed of a free electron is based on its total energy, and is not a set speed. The constant speed of light is specifically due to its not having any mass, whereas an electron has mass
 
  • #3
A good example of free electrons in a vacuum is the cloud of electrons that are around a hot cathode (thermionic emission) in a typical vacuum tube. A grid in the tube controls the electron density, called space charge, which in turn controls the electron current reaching the plate.
Bob S
 
  • #4
Is there a way to slow down electrons, bring them to complete stop?
 
  • #5
marion.s said:
Is there a way to slow down electrons, bring them to complete stop?

Yes, although you obviously not stop the motion complettely, it is possible to trap electrons in a reasonably well defined positon using magnetic fields. The principle is essentially the same as for ion traps.
Google Penning trap.
 
  • #6
What is electron velocity inside Penning trap?

Penning trap do not slow electrons down, or does it?Can anyone give some links about experiments describing how to bring electron to complete stop? I had a feeling that would be impossible, so I'd really like to see some experimental measurements of electron velocities in the range of 100 - 0 m/s.
 
  • #7
marion.s said:
Can anyone give some links about experiments describing how to bring electron to complete stop? I had a feeling that would be impossible, so I'd really like to see some experimental measurements of electron velocities in the range of 100 - 0 m/s.

You can slow down electrons in the conductor by reducing the electric field and cooling the conductor. Even if you nearly completely remove the electric field and reduce the temperature to near absolute zero, the electrons would still move around. The slowest would move at near zero velocities, the fastest at the Fermi velocity.
 
  • #8
the movement of a free electron in absolute zero and sans an electric field wouldn't be linear right? I would imagine at that point it would just be vibrating in place
 
  • #9
rhenretta said:
the movement of a free electron in absolute zero and sans an electric field wouldn't be linear right? I would imagine at that point it would just be vibrating in place
Imagine a single free electron at the center a cubic copper box. There are equal image charges on all six interior sides of the box (forget about fractional charges-it doesn't matter). As soon as the electron moves away from the center, the image charge on the closest side of the box increases. This increases the attraction of the electron to that side, and the electron accelerates away from the center of the box.

If the electron is in intergalactic space, it just keeps moving along, subject to the uncertainty principle: h-bar/2 = δx δp.
Bob S
 
  • #10
rhenretta said:
the movement of a free electron in absolute zero and sans an electric field wouldn't be linear right? I would imagine at that point it would just be vibrating in place

Yes, if you stretch the definition of vibrating. I guess better classical analogy would be a random walk.
 
  • #11
Bob S said:
If the electron is in intergalactic space, it just keeps moving along, subject to the uncertainty principle: h-bar/2 = δx δp.

And to the gravitational, electromagnetic, [...] fields. Strictly speaking even intergalactic space is not empty. There is cosmic background radiation, radiation from the stars and galaxies, etc.
 
  • #12
dmtr said:
You can slow down electrons in the conductor by reducing the electric field and cooling the conductor. Even if you nearly completely remove the electric field and reduce the temperature to near absolute zero, the electrons would still move around. The slowest would move at near zero velocities, the fastest at the Fermi velocity.

I don't think temperature has influence on electron velocities, "heat" is more about atoms and molecules. I don't think electrons velocity in low temperature superconductors ever come even close to zero. But, can't we measure this? Are there some experiments to measure electron velocities in superconductors or plasma? Are there some experiments that measure LINEAR electron velocities, like in electron beams? Can we slow down electron beams?

Can we make electrons in electron beam move at say 0.5 m/s?
 
  • #13
Bob S said:
Imagine a single free electron at the center a cubic copper box. There are equal image charges on all six interior sides of the box (forget about fractional charges-it doesn't matter). As soon as the electron moves away from the center, the image charge on the closest side of the box increases. This increases the attraction of the electron to that side, and the electron accelerates away from the center of the box.
Although I would like to know some range of velocities in low temp. superconductors and plasma, I'm not interested in "drift velocity" or some average velocity of electrons scattering, bouncing or jumping around in some confined area. Mostly, I'd like to know about linear velocity, when electrons are traveling in straight line, like in electron beam or alternatively in long, straight, superconducting wire.


If the electron is in intergalactic space, it just keeps moving along, subject to the uncertainty principle: h-bar/2 = δx δp.
Bob S

Ok, so what speed is that?

What is the minimum linear speed anyone ever observed electrons to move at?
...and has anyone ever managed to slow down electrons, what was the minimum velocity?
 
  • #14
marion.s said:
I don't think temperature has influence on electron velocities, "heat" is more about atoms and molecules. I don't think electrons velocity in low temperature superconductors ever come even close to zero. But, can't we measure this?

The answer here is Fermi velocity. But you are not going to get one velocity, rather it is going to be some probability distribution.

marion.s said:
Are there some experiments to measure electron velocities in superconductors or plasma? Are there some experiments that measure LINEAR electron velocities, like in electron beams? Can we slow down electron beams?
Can we make electrons in electron beam move at say 0.5 m/s?

Part of the answer here is Drift velocity. See http://en.wikipedia.org/wiki/Drift_velocity
 
  • #15
I'm not interested in Fermi energy, nor drift velocity. I'm talking about FREE electrons and LINEAR VELOCITY measured in meters per second. I would like to see some actual numbers, like - what is the minimum linear speed anyone ever observed electrons to move at? ...and, has anyone ever managed to slow down electrons, what was the minimum velocity?
 
  • #16
can that electron be slow enough to be immersed in a condensate without depleting it ?
 

Related to Speed of free electrons in vacuum, plasma and superconductors?

What is the speed of free electrons in vacuum?

The speed of free electrons in vacuum is approximately 2.998 x 10^8 m/s, which is the speed of light in a vacuum. This is known as the speed of light constant.

How does the speed of free electrons in vacuum compare to other materials?

Compared to other materials, the speed of free electrons in vacuum is significantly faster. In most materials, the speed of free electrons is much slower due to collisions with atoms and other factors. However, in vacuum, there are no atoms to impede the movement of electrons, allowing them to travel at the maximum speed possible.

What is the speed of free electrons in plasma?

The speed of free electrons in plasma varies depending on the temperature and density of the plasma. In general, the speed of free electrons in plasma is much faster than in a solid or liquid, but slower than in vacuum. This is because plasma is a partially ionized gas that still contains some neutral atoms, which can affect the movement of electrons.

Why do free electrons move differently in a superconductor?

In a superconductor, the speed of free electrons is zero. This is due to a phenomenon called perfect conductivity, where electrical resistance is completely eliminated. In a superconductor, electrons form pairs that move together without any resistance, allowing them to travel at an infinite speed.

Can the speed of free electrons in superconductors be affected by external factors?

The speed of free electrons in superconductors is not affected by external factors such as temperature or electric fields. This is because the movement of electrons in a superconductor is a collective phenomenon, rather than individual movements. Therefore, the speed remains constant regardless of external conditions.

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