Physics Forums

Thread Closed

Page 1 of 3   1   2   3  >

## atom self capacitance

can electron energy levels just be considered the self capacitance of an atom?

PhysOrg.com  physics news on PhysOrg.com  >> Promising doped zirconia>> Nanocrystals grow from liquid interface>> New insights into how materials transfer heat could lead to improved electronics

Looking at the definition of capacitance, the ratio between the charge and de potencial in a system of charges, I would say that in some sense your guess is right.  If I understand correctly, the capacitance gives you the charge that you have to introduce in a  conductor to increase the voltage up to 1V. In the case of self capacitance the reference for that voltage is an esphere of infinite radius. But this is a classical definition, and usually is used in macroscopid systems because the energy of the conductor is given by this easy relation $$E=\frac{Q^2}{2C}$$ But in a quantum system this rule is not true. So I would say that you can look at the energy levels as a self capacitance, but this is not useful because all the information is already in the energy levels, why to introduce another parameter?. Hope this helps.

I just thought it was an interesting concept, and was curious if was useful...  Using the Bohr hydrogen model with the capacitance equations: C = 4 * pi * electric_constant * bohr_radius = 5.8878e-21 F  $$E=\frac{Q^2}{2C}$$  E = (1.60217646e-19 C)^2 / (2*  5.8878e-21 F) = 13.60 eV

## atom self capacitance

Seems to work with inductance and LC resonance as well.

I have to say that this coincidence in the energies is strange.  Anyway to consider a single hydrogen nucleus as a conductor sphere is a very rough approximation, isn't it? Another point is that assuming your arguments as valid would imply that to introduce a second electron in the hydrogen atom you have to to provide again the same energy, this is not correct, as far as I know.  Regarding your second post, I don't understand what you try to say.

I'm not sure if this is correct.  I used the following equation to find  the inductance of ground state H:  ((bohr_radius^2) * electron_mass) / (elementary_charge^2) = 9.93734e-14 H  The units seem to work.   Then I tried using the L and C variables with the LC resonance equation: w = sqrt(1/LC) To get w = 4.1341e16  rad/s   or  f = 6.57968e15 hz  Then checked the "orbital frequency" of hydrogen with: f = v / wavelength Assumed the wavelength was equal to (2*pi*bohr_radius), and velocity of hydrogen electron (a * c)   f = (a*c) / (2*pi*bohr_radius) = 6.57968e15 hz

Mentor

Quote by cubeleg 					 				 				I have to say that this coincidence in the energies is strange.
It's not a coincidence. You put it in to get the Bohr radius, and then you get it out again.

Recognitions:
Gold Member

Quote by nuby 					 				 				I'm not sure if this is correct.  I used the following equation to find  the inductance of ground state H:  ((bohr_radius^2) * electron_mass) / (elementary_charge^2) = 9.93734e-14 H  The units seem to work.   Then I tried using the L and C variables with the LC resonance equation: w = sqrt(1/LC) To get w = 4.1341e16  rad/s   or  f = 6.57968e15 hz  Then checked the "orbital frequency" of hydrogen with: f = v / wavelength Assumed the wavelength was equal to (2*pi*bohr_radius), and velocity of hydrogen electron (a * c)   f = (a*c) / (2*pi*bohr_radius) = 6.57968e15 hz
Interesting topic, hope this isn't a dumb question, but how do you know the "velocity of hydrogen electron (a * c)" and what are a and c?

a = fine structure constant c = speed of light  (a*c) is the velocity of a ground state hydrogen electron according to the Bohr model.

Vanadium 50, or anyone else,    What do you make of this?

Mentor  Like a capacitor, an atom stores energy in electric fields, and I suppose one can calculate an "equivalent capacitance".  I'm not sure there's much physical insight to be gained here, as you're not going to plug one into a circuit.  Like an inductor, some atoms also store energy in magnetic fields, and I suppose one can calculate an "equivalent inductance".  Here, though, you've gone astray and assumed all of the energy is stored in the magnetic field.  That's not the case.  An LC circuit moves energy back and forth between the capacitor and the inductor.  This is not what happens in the atom.  The reason why you got the Rydberg constant out was that you put it in, in the form of the Bohr radius.

Like a capacitor, an atom stores energy in electric fields, and I suppose one can calculate an "equivalent capacitance". I'm not sure there's much physical insight to be gained here, as you're not going to plug one into a circuit.  Like an inductor, some atoms also store energy in magnetic fields, and I suppose one can calculate an "equivalent inductance". Here, though, you've gone astray and assumed all of the energy is stored in the magnetic field. That's not the case.  An LC circuit moves energy back and forth between the capacitor and the inductor. This is not what happens in the atom. The reason why you got the Rydberg constant out was that you put it in, in the form of the Bohr radius.
I have to agree with you that the coincidence is an artifact introduced in the "model".
About the physical sense of the capacitance is exactly what I try to say in my first post.
Regarding the LC, in my opinion, although the analogy is not very useful, the bohr model obtain those number assuming that the speed and potencial energy are equilibrated in fixed levels. This can be seen as current-voltage exchange, which essentialy is what you see in the LC circuit. But I insist that this a quite artificial point of view and all number are there as Vanadium50 correctly said, so is not surprising that it "works".

Recognitions:
Gold Member

Quote by nuby 					 				 				Vanadium 50, or anyone else,    What do you make of this?
The picture of a proton that this draws for me is an empty 3d shell 53 picometers in radius, much like you see in molecule pictures using the space filling options. There is no center to the proton, it is just a shell of charge, much like a Van der Graaf generator.

The "Shell theorem" from Newtons time suggests that the electron would feel no forces inside this shell. It also means protons and electrons dont crash into each other as electrons can simply pass right through protons (the proton is not a point charge)... and lots of other neat things...

Recognitions:
Gold Member

Quote by cubeleg 					 				 				I have to say that this coincidence in the energies is strange.  Anyway to consider a single hydrogen nucleus as a conductor sphere is a very rough approximation, isn't it? Another point is that assuming your arguments as valid would imply that to introduce a second electron in the hydrogen atom you have to to provide again the same energy, this is not correct, as far as I know.  Regarding your second post, I don't understand what you try to say.
In this kind of model, less energy would be needed for the second electron as one electron is inside the sphere providing a push against the second electron.

I just found a document regarding the "LC Bohr atom model", this guy did the same thing but took it a few steps further.   http://www.scielo.cl/pdf/ingeniare/v...cial/art03.pdf

Mentor  That "model" is wrong.    Equation 6 has him saying a given quantity of energy is in two places at once: in kinetic energy and in a magnetic field.  The rest of the paper has him rediscovering the Bohr-Sommerfeld model of the atom, albeit with less rigor, less generality, less motivation and less clarity, but keeping all the problems.    Had he written it in 1911, it might have been interesting.

Oh well..  It was the closest thing I could find to the above so I figured I'd post it.  I had a feeling it would have some issues.  Thanks for checking it out.

Thread Closed

Page 1 of 3   1   2   3  >

Thread Tools

|                                            |                               |         |
|--------------------------------------------|-------------------------------|---------|
| Similar Threads for: atom self capacitance |                               |         |
| Thread                                     | Forum                         | Replies |
|                                            | Introductory Physics Homework | 6       |
|                                            | Introductory Physics Homework | 2       |
|                                            | General Physics               | 1       |
|                                            | Introductory Physics Homework | 0       |
|                                            | Classical Physics             | 5       |
{"extraction_info": {"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 2, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0}, "config": {"markdown_headings": true, "markdown_code": true, "boilerplate_config": {"ratio_threshold": 0.18, "absolute_threshold": 10, "end_threshold": 15, "enable": false}, "remove_buttons": true, "remove_image_figures": true, "remove_link_clusters": true, "table_config": {"min_rows": 2, "min_cols": 3, "format": "github"}, "remove_chinese": true, "remove_edit_buttons": true, "extract_latex": true}, "english_confidence": 0.9445552229881287, "perplexity_flag": "middle"}