Electric field, electric charge, electron and positron.

[swansont]

I don't understand how that can slow down electrons. "Thermal" is just a description of kinetic state of some medium. Higher temperatures correspond to higher atom velocities or higher molecular vibrations/oscillations. Low temperature decreases velocities, but I don't think electron velocity changes, just this velocity of atoms or molecular vibrations. Electrons need their velocities to stay in their orbit, classically speaking. -- But anyhow, this is the question: how can electron microscopes produce different electron energies, how do they emit slow electrons?

 

A classical thermal ensemble follows a Maxwell-Boltzmann distribution of speeds. Some particles will be fast, some will be slow.

 

http://hyperphysics.phy-astr.gsu.edu/Hbase/kinetic/kintem.html

 

There are always some particles in the low-velocity part of the distribution.

 

 

 

Ok, so there is south and north magnetic pole, and whatever the orientation we can change it in arbitrary direction, yes? In fact, we should be able to spin this electron by influencing this magnetic dipole moment, just like electric motors do, and when we turn our spin induction magnets off, the electron should continue to spin, right?

 

No, we can't change it in an arbitrary direction — it's quantized. It will always have some orientation restrictions with respect to the field, and always have the same value.

 

http://en.wikipedia.org/wiki/Stern–Gerlach_experiment

[Sha31]

A classical thermal ensemble follows a Maxwell-Boltzmann distribution of speeds. Some particles will be fast, some will be slow.

 

http://hyperphysics.phy-astr.gsu.edu/Hbase/kinetic/kintem.html

 

There are always some particles in the low-velocity part of the distribution.

 

Those "particles" are atoms and molecules, not electrons. Can you prove to me electrons can actually go any slower than close-to-light and what is the technology used to achieve this? How can electron microscopes slow down electrons in electron beam, their linear velocity to something like 5,000 m/s? I think electrons, just like photons, can not go any slower than the speed of light.

 

 

No, we can't change it in an arbitrary direction — it's quantized. It will always have some orientation restrictions with respect to the field, and always have the same value.

 

http://en.wikipedia.org/wiki/Stern–Gerlach_experiment

 

- "If the particles are classical, "spinning" particles, then the distribution of their spin angular momentum vectors is taken to be truly random and each particle would be deflected up or down by a different amount, producing an even distribution on the screen of a detector."

 

 

This assumption does not need to apply to electron beams and electrons coming from the same source, or any group of electrons with the same velocity, as these electrons might be aligning their magnetic fields according to velocity vector, and most certainly they would be aligning their magnetic fields in relation to each other. So, it should not be surprising this experiment produces these results even if starting assumption does not apply.

 

 

What are they trying to establish anyway? That angular momentum is constant...

 

or/and

 

...that ORIENTATION of these two magnetic fields can be only along one axis?

[Mr Skeptic]

I think electrons, just like photons, can not go any slower than the speed of light.

 

What makes you think that the rest mass of an electron is zero?

[Sha31]

What makes you think that the rest mass of an electron is zero?

 

I didn't mean to say exactly the speed of light, but whatever is their usual speed in vacuum, something a little bit less than lightspeed I suppose.

 

What is the technology and physical principle based on which electron microscopes emit slow electrons? How do they produce different electron energies, how do they slow down electrons?

 

 

On the other hand, you are not far from what I'm trying to question here. I'm trying to figure out if there is such thing as mass in the real world at all, or is gravity force just an side-effect of different forms of kinetic energy of electromagnetic fields.

[Klaynos]

When swansont discussed thermal distributions there is nothing to stop the particles being electrons, why would there be that limitation? One example I can think of is an electron sea in a metal.

 

I didn't mean to say exactly the speed of light, but whatever is their usual speed in vacuum, something a little bit less than lightspeed I suppose.

 

Why do you think their "usual speed" is so high? I'm not sure that the concept of "usual speed" means anything, what's the "usual speed" of a car? And in what frame of reference?

 

In a CRT do you know the velocity of the electrons off of the filament before they are accelerated? If you can accelerate them, which we know you can, you can de-accelerate them by applying an opposite field.

 

Have a read of this and related articles:

 

http://en.wikipedia.org/wiki/Thermionic_emission

 

What is the technology and physical principle based on which electron microscopes emit slow electrons? How do they produce different electron energies, how do they slow down electrons?

 

See above, these electrons are then accelerated, depending on the field used changes their final energy. So the electron emitter does not change the energy of the electrons it generates, but those electrons are accelerated different amounts afterwards.

 

On the other hand, you are not far from what I'm trying to question here. I'm trying to figure out if there is such thing as mass in the real world at all, or is gravity force just an side-effect of different forms of kinetic energy of electromagnetic fields.

 

Charge seems to have nothing to do with mass.

[swansont]

Those "particles" are atoms and molecules, not electrons. Can you prove to me electrons can actually go any slower than close-to-light and what is the technology used to achieve this? How can electron microscopes slow down electrons in electron beam, their linear velocity to something like 5,000 m/s? I think electrons, just like photons, can not go any slower than the speed of light.

 

What phenomenon is there to prevent an electron from moving slowly?

[Sha31]

What phenomenon is there to prevent an electron from moving slowly?

 

I don't know. I also don't know why are you asking me questions. I've never seen any free electrons moving slowly, nor have I ever heard of slow moving electrons. If you can point me to some examples that should be sufficient to convince me, I'm not arguing, I'm just curious. I tried to google, but I can not find any particular velocities associated with electrons traveling trough different mediums, like there is for light.

 

 

However, I found something else...

 

http://en.wikipedia.org/wiki/Electron_microscope

- "The greater resolution and magnification of the electron microscope is because the de Broglie wavelength of an electron is much smaller than that of a photon of visible light."

 

http://en.wikipedia.org/wiki/De_Broglie_wavelength

- "In quantum mechanics, a matter wave or de Broglie wave is the wave (wave-particle duality) of matter. The de Broglie relations show that the wavelength is inversely proportional to the momentum of a particle and that the frequency is directly proportional to the particle's kinetic energy. The wavelength of matter is also called de Broglie wavelength."

 

 

...it seems this makes it even harder to distinguish between kinetic energy coming from linear velocity, angular momentum or mass, and now there is this frequency, some "vibration" as well.

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When swansont discussed thermal distributions there is nothing to stop the particles being electrons, why would there be that limitation? One example I can think of is an electron sea in a metal.

 

I don't know. I just want to see some numbers or range, some velocities, but specifically for electrons. It takes energy to knock electrons out of orbit, so when becoming 'free electrons' they will at least have some velocity proportional to its 'orbital energy', right?

 

 

Why do you think their "usual speed" is so high? I'm not sure that the concept of "usual speed" means anything, what's the "usual speed" of a car? And in what frame of reference?

 

I don't know, I'm asking. There is "usual speed" of photons in vacuum, so I expected there are some measurements of electron velocities similar to that.

 

Just how slow can we make electrons go?

Can we make them stop completely in one place?

 

 

In a CRT do you know the velocity of the electrons off of the filament before they are accelerated? If you can accelerate them, which we know you can, you can de-accelerate them by applying an opposite field.

 

Have a read of this and related articles:

 

http://en.wikipedia.org/wiki/Thermionic_emission

 

See above, these electrons are then accelerated, depending on the field used changes their final energy. So the electron emitter does not change the energy of the electrons it generates, but those electrons are accelerated different amounts afterwards.

 

Unfortunately article does not mention any velocities. I would think there must be some experimental measurements of electron beams passing through different mediums like vacuum, glass, water...

Edited December 15, 2009 by Sha31
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[Klaynos]

OK, I'll put it simply.

 

You can have an electron from 0m/s to infinitely close to (but not at) the speed of light in a vacuum.

 

http://prola.aps.org/abstract/PR/v113/i1/p110_1

 

http://prola.aps.org/abstract/PR/v98/i4/p889_1

 

Things are a little more complicated due to quantum mechanics, but remember spin is an intrinsic property not movement.

 

When you remove an electron from an orbital shell, if the work energy is say 3Energy units, and you give it 3.5Energy units the electron will have .5Energy units of KE, but if you give it 3Energy units the electron will become removed from the atom and have 0Energy units of KE, meaning it cannot be moving.

[swansont]

I don't know. I also don't know why are you asking me questions. I've never seen any free electrons moving slowly, nor have I ever heard of slow moving electrons. If you can point me to some examples that should be sufficient to convince me, I'm not arguing, I'm just curious. I tried to google, but I can not find any particular velocities associated with electrons traveling trough different mediums, like there is for light.

 

I ask because you made a claim, and I'm wondering what the physical basis is for that claim. How slowly electrons can be made to move is fundamentally a flawed question, because you can always look at a situation in the rest frame of the electron, as has already been mentioned.

 

However, I found something else...

 

http://en.wikipedia.org/wiki/Electron_microscope

- "The greater resolution and magnification of the electron microscope is because the de Broglie wavelength of an electron is much smaller than that of a photon of visible light."

 

http://en.wikipedia.org/wiki/De_Broglie_wavelength

- "In quantum mechanics, a matter wave or de Broglie wave is the wave (wave-particle duality) of matter. The de Broglie relations show that the wavelength is inversely proportional to the momentum of a particle and that the frequency is directly proportional to the particle's kinetic energy. The wavelength of matter is also called de Broglie wavelength."

 

 

...it seems this makes it even harder to distinguish between kinetic energy coming from linear velocity, angular momentum or mass, and now there is this frequency, some "vibration" as well.

 

Yeah, physics is quite involved. As I suggested before, taking a few classes would be invaluable, since you are trying to develop an understanding that took the rest of us several years' worth of study.

 

 

I don't know. I just want to see some numbers or range, some velocities, but specifically for electrons. It takes energy to knock electrons out of orbit, so when becoming 'free electrons' they will at least have some velocity proportional to its 'orbital energy', right?

 

No, as Klaynos has explained.

 

I don't know, I'm asking. There is "usual speed" of photons in vacuum, so I expected there are some measurements of electron velocities similar to that.

 

There is no such "usual speed" for electrons. Their speed depends on their kinetic energy, and you can add or subtract from that through various interactions.

[npts2020]

Sha31; If one has the right equipment, the speed of an electron can easily be measured by how much it deviates from its path of trajectory when passing through a known magnetic field. The more deviation=more time spent in the field=slower kinetic energy, or speed. In fact, if the electron is stationary or not moving fast enough the magnetic field will capture it.

[Mr Skeptic]

I didn't mean to say exactly the speed of light, but whatever is their usual speed in vacuum, something a little bit less than lightspeed I suppose.

 

What is the technology and physical principle based on which electron microscopes emit slow electrons? How do they produce different electron energies, how do they slow down electrons?

 

Actually electrons in a wire move very slowly on average (they bounce around a lot), so much so that you can walk faster than they move. X-ray machines generate x-rays by accelerating electrons and then quickly stopping them on a plate of metal. Electrons can be accelerated by an electric field, and decelerated by an opposing electric field or by hitting something (especially a conductor). Particle colliders take this to an absurd level.

 

Now, a minimum speed for electrons may be reasonable. If you were to bring them to a complete halt, then funny things start happening with their wavelength. Bringing them to a complete halt would also require a temperature of zero Kelvin, which is unattainable. I don't know if there would be a specific lower limit though. This is not unique to electrons either.

 

On the other hand, you are not far from what I'm trying to question here. I'm trying to figure out if there is such thing as mass in the real world at all, or is gravity force just an side-effect of different forms of kinetic energy of electromagnetic fields.

 

Well, that seems interesting, but remember that your ideas have to account for the real world. And remember that electromagnetic fields can be blocked, and can repel as well as attract. So you need to find a way to make your thing behave like gravity.

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I don't know. I also don't know why are you asking me questions.

 

He's helping you make your theory work. Unless you are talking fairy tales, your proposed theory needs to account for the real world. Believe me, swansont knows a thing or two about the real world.

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swansont, does spin angular momentum count for the de Broglie wavelength?

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There is no such "usual speed" for electrons. Their speed depends on their kinetic energy, and you can add or subtract from that through various interactions.

 

Unlike light, where adding energy to or removing energy from photons will change their color instead of their speed.

[swansont]

swansont, does spin angular momentum count for the de Broglie wavelength?

 

No. It's given by h/p . Linear momentum is what matters

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Actually electrons in a wire move very slowly on average (they bounce around a lot), so much so that you can walk faster than they move. X-ray machines generate x-rays by accelerating electrons and then quickly stopping them on a plate of metal. Electrons can be accelerated by an electric field, and decelerated by an opposing electric field or by hitting something (especially a conductor). Particle colliders take this to an absurd level.

 

Now, a minimum speed for electrons may be reasonable. If you were to bring them to a complete halt, then funny things start happening with their wavelength. Bringing them to a complete halt would also require a temperature of zero Kelvin, which is unattainable. I don't know if there would be a specific lower limit though. This is not unique to electrons either.

 

To be precise, the small drift velocity is the net motion on top of the random thermal motion. But they are continually undergoing collisions, and some electron is going to be brought to rest, or very close to it, during a collision. Then it will interact some more and start moving faster. That's all part of saying that they would have a distribution of speeds, similar to atoms having a Maxwell-Boltzmann distribution..

 

Anyway, single electrons have been cooled to sub-Kelvin temperatures in Penning traps. They're trapped, and accelerating due to cyclotron motion, so they radiate and eventually reach the ground state. The trick apparently is to cool the surrounding equipment so that thermal radiation does not excite them.

[Sha31]

When you remove an electron from an orbital shell' date=' if the work energy is say 3Energy units, and you give it 3.5Energy units the electron will have .5Energy units of KE, but if you give it 3Energy units the electron will become removed from the atom and have 0Energy units of KE, meaning it cannot be moving.[/quote']

 

Can you provide some reference for that? I have to disagree. I expect there to be 'escape velocity', so if electron is knocked just a little bit off, it would get attracted back.

 

 

Things are a little more complicated due to quantum mechanics, but remember spin is an intrinsic property not movement.

 

Ok, but these two magnetic poles can have any orientation, which we can see when we rotate permanent magnet in hand, so why we could not spin single magnetic dipole (electron) with external magnetic fields just like we can spin bar magnet? I'm talking about axis of rotation that is perpendicular to axis along these two magnetic poles.

 

 

OK, I'll put it simply.

 

You can have an electron from 0m/s to infinitely close to (but not at) the speed of light in a vacuum.

 

Ok. Can you just provide some reference to that?

 

 

 

http://prola.aps.org/abstract/PR/v113/i1/p110_1

 

http://prola.aps.org/abstract/PR/v98/i4/p889_1

 

There is no mention of any velocities there.

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I ask because you made a claim' date=' and I'm wondering what the physical basis is for that claim. How slowly electrons can be made to move is fundamentally a flawed question, because you can always look at a situation in the rest frame of the electron, as has already been mentioned.

[/quote']

 

1.) I assure you, I mean only to ask question, and you said:

- "An individual electron can have an arbitrarily small speed."

 

...so, I'm merely questioning your claim.

Can you provide some evidence to support your claim please?

 

 

 

2.) Reference frame? What are you talking about? In the same reference frame that we use to measure the speed of light, of course. Surely not electron's reference frame, I want to know VELOCITY. What is kinetic energy of electron its own frame of reference anyway, zero?

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Sha31; If one has the right equipment, the speed of an electron can easily be measured by how much it deviates from its path of trajectory when passing through a known magnetic field. The more deviation=more time spent in the field=slower kinetic energy, or speed. In fact, if the electron is stationary or not moving fast enough the magnetic field will capture it.

 

I disagree with all that. Can you provide some evidence to support what you said?

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Actually electrons in a wire move very slowly on average (they bounce around a lot)' date=' so much so that you can walk faster than they move. X-ray machines generate x-rays by accelerating electrons and then quickly stopping them on a plate of metal.

[/quote']

 

Ok, let me once more underline that I'm talking about "free electrons" and real velocity, like in electron beam, not average drift velocity, scattering, bouncing or similar.

 

 

Electrons can be accelerated by an electric field, and decelerated by an opposing electric field or by hitting something (especially a conductor). Particle colliders take this to an absurd level.

 

Can you just provide some reference about slowing down electrons?

 

 

 

Now, a minimum speed for electrons may be reasonable. If you were to bring them to a complete halt, then funny things start happening with their wavelength.

 

Where do you find that information? Can give some links about that?

 

 

Bringing them to a complete halt would also require a temperature of zero Kelvin, which is unattainable. I don't know if there would be a specific lower limit though. This is not unique to electrons either.

 

Now we need zero temperature?

Why can't electric and magnetic fields do it anymore?

 

 

 

Unlike light, where adding energy to or removing energy from photons will change their color instead of their speed.

 

But then, how do you know when you add energy to electrons you are in fact not just increasing their de Broglie frequency? How do we measure electron velocity? What exactly can we measure?

[Mr Skeptic]

You can have an electron from 0m/s to infinitely close to (but not at) the speed of light in a vacuum.

 

I too would like a reference for that. I could accept getting arbitrarily close to 0 m/s, but at exactly 0 weird stuff starts happening too. Let's say 2 electrons moving at exactly 0 m/s, or one at 0 m/s in a frame shown to be inertial.

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Can you just provide some reference about slowing down electrons?

 

Sure, anything that accelerates electrons slows them down in different reference frame. Or did you also not accept that electrons can be sped up?

 

Where do you find that information? Can give some links about that?

 

You already shared the links, the de Broglie wavelength. What happens in that equation when velocity and therefore momentum (the p term) goes to zero?

 

Now we need zero temperature?

Why can't electric and magnetic fields do it anymore?

 

Well, if you want more than one electron to be still they need to have zero temperature. Temperature is a measure of the kinetic energy of particles, so if it is not absolute zero then they have kinetic energy by definition.

 

But then, how do you know when you add energy to electrons you are in fact not just increasing their de Broglie frequency? How do we measure electron velocity? What exactly can we measure?

 

Well adding energy to the electrons will most definitely decrease their de Broglie wavelegth and increase their de Broglie frequency. In case you were wondering, an electron microscope needs fast electrons for more resolution, since the faster ones have a shorter wavelength.

 

Anyhow, throw an electron through an electric field and measure its deflection. The slower it was going the more it will be deflected because it spends more time in the field, just as if you tossed a baseball through a wind tunnel (perpendicular to the airflow).

[Sha31]

Sure' date=' anything that accelerates electrons slows them down in different reference frame. Or did you also not accept that electrons can be sped up?

[/quote']

 

I accept all evidence for consideration. Right now I'd like to read something about 'slowing down electrons' specifically, and I'd like to see some numbers, some velocities and the description of what technology was used, about the procedure with which measurements were taken. I also want to know how do they measure electron velocity in particle accelerators, v= distance/time?

 

 

You already shared the links, the de Broglie wavelength. What happens in that equation when velocity and therefore momentum (the p term) goes to zero?

 

Yes, ok. At least we agree there is something strange (impossible) about electron zero velocity. Anyway, I thought you were referring to some experiments.

 

 

Well, if you want more than one electron to be still they need to have zero temperature. Temperature is a measure of the kinetic energy of particles, so if it is not absolute zero then they have kinetic energy by definition.

 

I'm talking about plasma, about free electrons and electron beams. Normally "temperature" is about atoms and molecules, but in any case, if you can show me example of electron plasma or electron beam where electrons can move at some "slow" or different velocities, than you will convince me.

 

 

 

Anyhow, throw an electron through an electric field and measure its deflection. The slower it was going the more it will be deflected because it spends more time in the field, just as if you tossed a baseball through a wind tunnel (perpendicular to the airflow).

 

But, you see, you don't know what's kinetics and what's mass. Instead of fast moving low-mass charge (electron) that could be slow moving large-mass charge (muon), and you would not know the difference, no?

 

 

Is ,<1>de Broglie frequency<1> actually describing <2>linear velocity<2>, or are these two variables independent and each can contribute to total electron energy by itself?

[npts2020]

Sha31; google experiments/electron speed. The first few (of the over half million) hits all reference what you are asking about.

[Sha31]

Well' date=' if you want more than one electron to be still they need to have zero temperature. Temperature is a measure of the kinetic energy of particles, so if it is not absolute zero then they have kinetic energy by definition.

[/quote']

 

Another one on zero temperature.

 

Consider superconductivity of certain materials at very low temperatures, where electrons kind of get free like in plasma. This very effect of *super-conducting* directly implies electrons move at very high velocities, maybe even very close to lightspeed, regardless of very low temperatures. So, are there any measurements of this super conductivity expressed in velocity of electrons? What is supposed to be velocity of electrons in superconducting wire?

[Mr Skeptic]

No, electrons in superconducting materials move very slowly (just run the numbers yourself, how many moles of electrons are free to move, and how much current is there). What superconductors have is no resistance, so electrons don't go bouncing off atoms the wrong way and turning their energy into vibrations of the atoms in the material (aka heat)

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I accept all evidence for consideration. Right now I'd like to read something about 'slowing down electrons' specifically, and I'd like to see some numbers, some velocities and the description of what technology was used, about the procedure with which measurements were taken. I also want to know how do they measure electron velocity in particle accelerators, v= distance/time?

 

Is that a yes, you accept that electrons can be accelerated?

 

I'm talking about plasma, about free electrons and electron beams. Normally "temperature" is about atoms and molecules, but in any case, if you can show me example of electron plasma or electron beam where electrons can move at some "slow" or different velocities, than you will convince me.

 

The same terminology can be applied. If you are talking about beams, then you split the components into the directed kinetic energy of the beam as a whole, and the kinetic energy in random directions of the electrons due to their temperature. If your beam is moving slowly enough, the velocity due to temperature will be greater than that of the beam as a whole.

 

But, you see, you don't know what's kinetics and what's mass. Instead of fast moving low-mass charge (electron) that could be slow moving large-mass charge (muon), and you would not know the difference, no?

 

Not in that device. But then all you have to do is put the electrons in a magnetic field, where they will curve perpendicular to the magnetic field lines. This way you can measure the charge-mass ratio via the radius of the circle they travel in. I have done this myself btw. http://en.wikipedia.org/wiki/Mass-to-charge_ratio

 

Is ,<1>de Broglie frequency<1> actually describing <2>linear velocity<2>, or are these two variables independent and each can contribute to total electron energy by itself?

 

Don't confuse velocity with momentum. The de Broglie frequency and wavelength are directly related to the momentum, as you should know.

[Sha31]

No, electrons in superconducting materials move very slowly (just run the numbers yourself, how many moles of electrons are free to move, and how much current is there). What superconductors have is no resistance, so electrons don't go bouncing off atoms the wrong way and turning their energy into vibrations of the atoms in the material (aka heat)

 

I don't believe you. C'mon, just give me some links with some numbers.

 

 

Is that a yes, you accept that electrons can be accelerated?

 

All I want is some reference, just give some, or not. Yes, I accept electrons can be accelerated. Now, I want to understand how electron microscope can produce low velocity electrons. I'm also interested to know about how to slow down electrons to zero velocity. And, I want to know average velocities of electrons in superconductors at low temperatures.

 

 

But then all you have to do is put the electrons in a magnetic field, where they will curve perpendicular to the magnetic field lines. This way you can measure the charge-mass ratio via the radius of the circle they travel in. I have done this myself btw. http://en.wikipedia.org/wiki/Mass-to-charge_ratio

 

You mean like this:

 

Yes, that's fine... so what was the velocity?

What is the velocity of these electrons on the photo?

 

 

However, my whole point is to distinguish between ALL the kinetics and mass, so 'linear velocity' as calculated with "v=s/t" is the only acceptable one.

 

The de Broglie frequency and wavelength are directly related to the momentum, as you should know.

 

Let me rephrase it:

 

1.) Can de Broglie frequency be zero with non-zero linear velocity?

2.) Can de Broglie frequency be non-zero with zero linear velocity?

Edited December 16, 2009 by Sha31

[Mr Skeptic]

I don't believe you. C'mon, just give me some links with some numbers.

 

Why a reference when you can see for yourself?

 

Yes, I accept electrons can be accelerated.

 

Very well, acceleration means a change in velocity. It can be an increase in velocity or a decrease. If electrons can be accelerated it logically necessitates that they can be decelerated.

 

For example, suppose you have a reference frame where you have an approximately stationary electron inside a stationary accelerator that accelerates the electron to 1,000 m/s east. Now, you are in an airplane moving 1,000 m/s east, and you see an electron in an accelerator, both moving 1,000 m/s west relative to you. The accelerator slows the electron to a halt (approximately).

 

You mean like this:

 

Yes, that's fine... so what was the velocity?

What is the velocity of these electrons on the photo?

 

That device does not measure velocity, it measures mass/charge ratio as you asked for (ie proof that it is an electron).

 

However, my whole point is to distinguish between ALL the kinetics and mass, so 'linear velocity' as calculated with "v=s/t" is the only acceptable one.

 

???

 

Let me rephrase it:

 

1.) Can de Broglie frequency be zero with non-zero linear velocity?

 

No, you would need zero momentum (therefore zero velocity) to get a de Broglie frequency of zero. I don't think you can get that in practice.

 

2.) Can de Broglie frequency be non-zero with zero linear velocity?

 

No, but again I don't think you can get anything to zero velocity.

[swansont]

Can you provide some reference for that? I have to disagree. I expect there to be 'escape velocity', so if electron is knocked just a little bit off, it would get attracted back.

 

The reference for this, and several other topics, is an introductory physics text. It's a huge difficulty trying to get through your many misconceptions about basic physics.

[Sha31]

The reference for this' date=' and several other topics, is an introductory physics text. It's a huge diffic...

 

[b']- "An individual electron can have an arbitrarily small speed."[/b]

 

I challenge you to provide evidence for your claim.

[insane_alien]

http://www.cfa.harvard.edu/itamp/slowelectrons.html#anchor636597 < many of the papers here deal with electrons with KE's of ~100eV

 

a tv will produce several keV electrons and particle colliders will provide GeV electrons.

 

this definitely indicates that they have an arbitrary speed.

[Klaynos]

Can you provide some reference for that? I have to disagree. I expect there to be 'escape velocity', so if electron is knocked just a little bit off, it would get attracted back.

 

Physically why would you expect an "escape velocity" they are not classical orbits. It is knocked out of the bound state, this takes energy. It is possible that it will be rebound later but immediately after it has been removed it is unbound.

 

http://hyperphysics.phy-astr.gsu.edu/HBASE/mod1.html#c5

 

Ok, but these two magnetic poles can have any orientation, which we can see when we rotate permanent magnet in hand, so why we could not spin single magnetic dipole (electron) with external magnetic fields just like we can spin bar magnet? I'm talking about axis of rotation that is perpendicular to axis along these two magnetic poles.

 

Not really magnetic poles, they are intrinsic spin angular momentum.

 

http://en.wikipedia.org/wiki/Spin_%28physics%29

 

There is no axis of rotation, hence intrinsic.

 

Ok. Can you just provide some reference to that?

 

There is no mention of any velocities there.

 

The two refernces I provide give KE which is related to velocity through a well known equation, as the KE goes to 0 as does the velocity.

 

Mr Skeptic, for simplicity I'm ignoring quantum effects and treating the electron as a classical particle, for the sake of the OP we need to get the easier physics understood first.

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Two other points:

 

Most UG general texts on physics will cover this stuff.

 

Temperature is a measure of the average KE of an ensemble of things... it's not really fair to use it for a single electron.

[swansont]

I challenge you to provide evidence for your claim.

 

I refer you to the answer I gave some moments ago. If you had learned about thermal speed distributions, you would not be asking the question. However, this requires that you take some physics classes. I'm not sure "take a thermodynamics class and all of the prerequisites" counts as evidence, per se, but then, I think the challenge to present evidence here is becoming absurd.

 

In case you missed the earlier post about electrons in a Penning trap, though,

 

The trap and the electron's cyclotron motion are cooled to about 100 milliKelvin

 

http://hussle.harvard.edu/~gabrielse/gabrielse/overviews/ElectronMagneticMoment/ElectronMagneticMoment.html

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Anyway, single electrons have been cooled to sub-Kelvin temperatures in Penning traps. They're trapped, and accelerating due to cyclotron motion, so they radiate and eventually reach the ground state. The trick apparently is to cool the surrounding equipment so that thermal radiation does not excite them.

 

Just had a chat with someone who has done such experiments. The cyclotron radiation cools the cyclotron motion, but not the orthogonal axial motion. For that, they introduced a loop with a resistor, so that the electron (which has a magnetic moment) saw an inductive load, and removed the energy that way. Which is a pretty cool experiment, IMO.

Edited December 16, 2009 by swansont
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