Electrons and protons

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  • #1
bobie
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Main Question or Discussion Point

Hi,
suppose we have a proton at point A and an electron at point B, at a distance of 1cm , separated by a screen.

If we remove the screen one would expect the particles to meet and clash somewhere near point A, but I read this never happens.

Can you explain why it's so and what exactly happen in reality?, and what is PE and what are final speeds?
Thanks
 

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  • #2
UltrafastPED
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PE is the potential energy; it is the work that would have been required to separate them.

I would expect the electron to be (a) kicked off in some hyperbolic path, or (b) some elliptical path. As energy is bled off the two will become a hydrogen atom in some excited state.

You need very high energies for the electron to "crash" into the proton.
 
  • #3
bobie
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I would expect the electron to be (a) kicked off in some hyperbolic path, or (b) some elliptical path.

You need very high energies for the electron to "crash" into the proton.
As both particles attract each other, why don't they follow a straight line?

What energy is required to make it land on the proton?
 
  • #4
UltrafastPED
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You are asking me to explain quantum mechanical behavior of sub-atomic particles ... this is how people thought prior to 1910. Look up the Rutherford experiments.

As for what happens, see this article on positronium:
http://en.wikipedia.org/wiki/Positronium
 
  • #5
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Particle are not like billard balls.
The screen wouldn't work, but let's just assume you put a proton and an electron somewhere in space. If you have a perfect vacuum: They would accelerate towards each other, and probably form a hydrogen atom. It is hard to prepare that, however - electron and proton have to come very close to each other to do that. If one of the particles started with some initial velocity, they will probably orbit each other for a while. Accelerated charges radiate, so the orbit will decay and you end up with a hydrogen atom as well.
 
  • #6
bobie
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They would accelerate towards each other, and probably form a hydrogen atom..
That is what I read, I wounder if you can tell me roughly at what point the electron leaves the straight path toward the proton , and what kind of forces make it deflect, is it magnetic force?
 
  • #7
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There is no classical "deflection" and the final state has the same symmetry as the initial state.
It is quantum mechanics, classical physics is not appropriate to describe it.
 
  • #8
bobie
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Thanks!
Do you happen to know a link or an applet where to see how it works?
 
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  • #9
bobie
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You are asking me to explain quantum mechanical behavior of
It is quantum mechanics, classical physics is not appropriate to describe it.
Does that mean that QM is only complicated math and has no explanation of the forces, or that the forces are too complex to explain?
 
  • #10
UltrafastPED
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It means that classical ideas break down in the quantum world. This has been know since at least 1900 when Planck's law was published.

Thus your "intuition" of what should happen needs to be informed by the physical knowledge of what _does_ happen. For example, when you ionize hydrogen gas the electrons don't fall into the nucleus; you get a hydrogen atom back, and these combine to form hydrogen molecules.

It _is_ possible to drive an electron into a proton with the electron then scattering from the "partons" which make up the proton (now known as quarks), or to even break up the proton. But these require very high energies.
 
  • #11
UltrafastPED
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BTW, QM is usually solved using energy, and not forces. The forces are converted to potential energy which then appears in the Shroedinger equation.

The same can be done for mechanical problems; these techniques are studied in a course on analytical mechanics where you will learn about Lagrangians and Hamiltonians. The ideas are a few hundred years old now:
http://en.wikipedia.org/wiki/History_of_classical_mechanics

OTOH quantum physics starts about 1900, and quantum mechanics starts in 1924/5:
http://en.wikipedia.org/wiki/History_of_quantum_mechanics
 
  • #12
bobie
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BTW, QM is usually solved using energy, and not forces. ]
Pardon my ignorance, but it's QM [or whatever theory] that should solve problems i.e. to explain reality.

In this instance the problem is why an opposite charge is not attracted in a straight line. Classical Physics has no solution.
If QM has an explanation it doesn't matter if you use energy instead of forces, its process should be explainable in a clear way that makes sense. There must be some energy-force that bends its path, anyway.
 
  • #13
UltrafastPED
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Last edited:
  • #14
bobie
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I am sorry I'm thick, but I do not see the point.
You can call it reality, or events, or phenomena or random whatever, but you are describing, explaing something-real-imaginary-random-allucination,... else you sut up shop.
QM considers the phenomenon , the issue at hand? Gives a decription-explanation whatever? what is it ?
Thanks for your time, ultrafast!
 
  • #15
UltrafastPED
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I don't think that I can provide an "explanation" which will satisfy you.

Solving for the hydrogen atom is difficult enough; you will spend several lectures on this in an undergraduate course, or a happy weekend solving it for yourself in a more advanced course:
see http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydsch.html

But the problem that you have posed is more difficult. Many problems can be stated, but are difficult to carry out mathematically.

Your original question was "Can you explain why it's so and what exactly happen in reality?" I told you what would happen - what the final possible states of the system are. You also asked for the potential energy (which you can easily calculate for yourself based on the charges on the two particles, and their initial separation).

If you have the potential energy you can estimate the final speeds from PE = sum of their kinetic energies. This requires that you calculate the momenta for each particle: by Newton's third law of motion you expect the momenta to be equal but opposite (for classical objects), so their magnitudes are m_e x V_e = m_p x V_p, and the sum of the kinetic energies at the "collision" is equal to the total potential energy: so two equations with two unknown velocities.

So go ahead and carry out the classical calculations!

But they won't tell you what "actually happens".
 
  • #16
bobie
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But they won't tell you what "actually happens".
Thanks for your efforts, but by that I did not mean anything detailed, just to know the actual path of the particles and the forces(or energies as you call it) that cause that path. And all that before it becomes an H-atom.
As simple as That.

I must conclude that QM has not yet found an explanation for that, and nobody really knows how it works.
 
  • #17
ZapperZ
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I must conclude that QM has not yet found an explanation for that, and nobody really knows how it works.
And you arrive at this conclusion based on what? A careful study of QM, or simply reading stuff on the web? And you trust that kind of "knowledge"? You know LESS about how QM works that many of the people who responded to you in this thread!

This is now veering on philosophy and personal tastes. If you wish to learn about QM, then please do so. However, if you think that you know more about such subject matter as to make your own conclusion based on superficial knowledge, then this thread will end very soon.

Zz.
 
  • #18
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I must conclude that QM has not yet found an explanation for that, and nobody really knows how it works.
That is called "jumping to a conclusion". It is a pretty big jump to a pretty bad conclusion.
 
  • #19
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Thanks for your efforts, but by that I did not mean anything detailed, just to know the actual path of the particles and the forces(or energies as you call it) that cause that path. And all that before it becomes an H-atom.
As simple as That.

I must conclude that QM has not yet found an explanation for that, and nobody really knows how it works.
There is no single, classical "path" the electron follows, in the same way as there is no single position where the electron "is".
You can describe electron and proton with wave-functions, and calculate the evolution of those wave-functions. It is complicated, but it is possible. The result will keep its symmetry all the time, and you end up with radiation and a hydrogen atom, probably in a superposition of multiple states.
 
  • #20
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I must conclude that QM has not yet found an explanation for that, and nobody really knows how it works.
You should've concluded instead that you don't really understand QM.

Note that there's no need for a deflection because in the lower energy shell the electron doesn't have any angular momentum around the proton. The electron IS NOT orbiting the proton.
 
  • #21
.Scott
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Can you explain why it's so and what exactly happen in reality?, and what is PE and what are final speeds?
Thanks
The first problem with you problem is that you are holding both particles steady at a distance of 1cm from each other. In fact, these particles are not precise enough to allow that. Heisenberg Uncertainty will limit how steady these particles can hold their positions. What really happens is that these particles will spread about about the points where you are trying to hold them.

Next you let them go - and they begin falling towards each other. At this point, you need to deal with them - or at least the electron - as waves. If you insist on dealing with the electron as a particle, then bear in mind that this particle is spread over an area and consists of a cloud of virtual particles. These particle fall towards the proton along a variety of trajectories and, in the process, constructively and destructively interfere with other - so much for dealing with them as particles.

At 1cm, the electron will flitter about as a free electron until it looses energy - by emitting a photon and dropping into an an electron orbital about the proton. Once in this orbital, it will no longer make any sense to talk about the position or trajectory of the electron. It will immediately fill up the entire orbital being constrained only by its energy and constructive and destructive interference. It will not collide with the proton because that is a region of destructive interference where there is no chance of finding the electron.

If I've mischaracterized any of this, please corrected me.
 
  • #22
UltrafastPED
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I've tried to provide factual information which I understand and can support; perhaps my PhD in physics is not up to the task!
 
  • #23
Khashishi
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The answer depends on how set up the experiment, and how you measure the results. In real experiments, it's very hard to deal with single protons and single electrons.
 
  • #24
.Scott
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I am sorry I'm thick, but I do not see the point.
You can call it reality, or events, or phenomena or random whatever, but you are describing, explaining something-real-imaginary-random-allucination,... else you sut up shop.
QM considers the phenomenon , the issue at hand? Gives a description-explanation whatever? what is it ?
Thanks for your time, ultrafast!
The problem is that you have this notion of electrons and protons that is incorrect. In the macroscopic world, an object traveling from point A to point B will follow a specific path. But is the world of QM, a particle may be emitted from an approximately known source, then detected at another approximately known location, and there is nothing "real" about a path drawn from emitter to detector. So when you ask when does the electron veer from its straight path, the answer is "when it became an electron". There are conditions, for example in a cathode ray tube, when electrons will seem to behave like little bullets. But that is an approximation of their behavior that cannot be used in your example.
 
  • #25
bobie
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You should've concluded instead that you don't really understand QM.
.
Surely I do not know and , of course , do not understand QM.

But the point is that it is a branch of physics, science that studies , describes and explain what we called the world, the universe, phenomena, reality.
Now , whatever interpretation it gives of the world, of the electron (etc) if it is a particle a wave or a poltergeist, does not change the phenomenon we observe of an apple being attracted by the Earth or an electron by a proton, cation.
An electron is attracted by a positive charge roughly by a straigth line ( I hope this is still valid: http://en.wikipedia.org/wiki/Electric_field#Electrostatic_fields) and as Scott confirmed, behave roughly like a bullet in a cathodic tube.
If the positive charge is free, its behaviour is different, even though the electron is exactly the same , be it a particle, a wave or whatever and if it follows a discernible path or not.
I am just asking what makes this behaviour different.
Is it not a legitimate question? If it is did I miss the answer?

I am sorry I wasted your time, I apologize, and stop posting.
 

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