Physics Help Forum First Bohr Track Radius

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 Aug 21st 2018, 10:41 PM #1 Banned   Join Date: Mar 2018 Location: Xinhui Guangdong Province China Posts: 118 First Bohr Track Radius Ok,change an ordinary topic. The wave function of electron moveing in Coulomb field contains the First Bohr Track Radius a0. But a0 is calculated with method of classical particle moving in circular track and according to classical electromagnetism, it's said that radiation of electromagnetic wave will occur and lead to the collapse of the atom. Is a0 not physical in atom or some problem with classical electromagnetism? If it's the latter, what's it? Thanks.
Aug 21st 2018, 11:01 PM   #2

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 Originally Posted by htam9876 Ok,change an ordinary topic. The wave function of electron moveing in Coulomb field contains the First Bohr Track Radius a0. But a0 is calculated with method of classical particle moving in circular track and according to classical electromagnetism, it's said that radiation of electromagnetic wave will occur and lead to the collapse of the atom. Is a0 not physical in atom or some problem with classical electromagnetism? If it's the latter, what's it? Thanks.
For all its use I think the Bohr model really needs to be retired. It does a good idea of calculating a number of properties ($\displaystyle a_0$ as you mentioned) but it is a lousy model because it not quantum mechanical.

The main point here is that the Bohr model suggests that an electron circles the atom in a particular path. The electron actually exists in an undetermined state until a measurement is made, as you correctly pointed out. Quantum Mechanically speaking the "averaged position" (called an "expectation value") of the electron in it's lowest energy state is $\displaystyle a_0$.

-Dan
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 Aug 21st 2018, 11:38 PM #3 Banned   Join Date: Mar 2018 Location: Xinhui Guangdong Province China Posts: 118 ... Thanks for your explanation. But I see that the equation of a0 in QM is just that one of Bohr calculated ...three elements :Plank constant, mass and charge...
Aug 22nd 2018, 02:18 AM   #4
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 Originally Posted by htam9876 Thanks for your explanation. But I see that the equation of a0 in QM is just that one of Bohr calculated ...three elements :Plank constant, mass and charge...
Yes, but it is used as a reference radius (a bit like a unit), not as a truthful statement about the actual orbital radius of an orbital electron. The PDF of orbital electrons is often not even spherical.

 Aug 22nd 2018, 05:00 AM #5 Senior Member     Join Date: Jun 2016 Location: England Posts: 1,085 Bohr used the best knowledge of the time to make one of the first reasonable models of the simpler electron "orbitals". However even then it was recognised that it has some serious limitations and flaws, (like the electromagnetic radiation that would be classically expected from a moving electron). So yes the Bohr model works Ok for the a0 "orbital", but it quickly falls down for more complex situations. Latter models (QM) were developed precisely because the Bohr model was known to be deficient. topsquark likes this. __________________ ~\o/~
 Aug 25th 2018, 03:51 AM #6 Banned   Join Date: Mar 2018 Location: Xinhui Guangdong Province China Posts: 118 ... I see a thread here in China, it ask a question: energy and mass which one first(exist in cosmos)? it's so funny that I just can't hold myself and give a reply: in men's eye, it will be a logic never to be made clear, while in the eye of cosmos, it's just one thing two forms.
Aug 25th 2018, 10:28 AM   #7

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 Originally Posted by htam9876 I see a thread here in China, it ask a question: energy and mass which one first(exist in cosmos)? it's so funny that I just can't hold myself and give a reply: in men's eye, it will be a logic never to be made clear, while in the eye of cosmos, it's just one thing two forms.
Energy and matter aren't really interchangeable but if you have matter you have energy; if you have energy you have matter. They don't exist separately.

What does this have to do with the Bohr model?

-Dan
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 Aug 25th 2018, 05:22 PM #8 Banned   Join Date: Mar 2018 Location: Xinhui Guangdong Province China Posts: 118 ... I just feel something alike. That logic unclear again. Can we see this regular world if the electron in atom only have wave character?
Aug 25th 2018, 08:02 PM   #9

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 Originally Posted by htam9876 I just feel something alike. That logic unclear again. Can we see this regular world if the electron in atom only have wave character?
If we don't try to look at individual electrons we are good. The atom itself is in an indeterminate state and we see them just fine with an electron microscope. But the images do come out a bit fuzzy at the edges and if you have two atoms close together they "smear out" a bit between them. This is what you would typically expect out of a system with a probabilistic nature. FYI: A few years back IBM "printed" it's name by lining up Xenon atoms on a substrate. Pretty cool. The atoms come out looking like dots.

-Dan
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Last edited by topsquark; Aug 25th 2018 at 08:06 PM.

 Aug 25th 2018, 08:49 PM #10 Banned   Join Date: Mar 2018 Location: Xinhui Guangdong Province China Posts: 118 ... Dear dragon, it will take me sometime to understand your post because I can't find some words in my dictionary. I hope that one day I am honored to see the electronic microscope under your instruction.It's so interesting. Now I am just confused in logic. The wave character and the particle characer, which one first(exist in cosmos)?