Talking Physics

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@DanHannard @Newmanphysics orbital angular momentum given by integers of h bar, which leads to the Bohr model of the atom

— Steven Cooke (@SteveTeachPhys) July 21, 2016

and there is a whole new discussion from Steve’s blog about the new energy description to be had in another thread.
However what has initially interested me is the similarities and differences between the Earth orbiting the Sun and an electron “orbiting” a proton. One is a system with a mass in another masses field and one is a charge in another charges field.

 

I seem to remember from mu undergraduate days a semi classical approach and the idea of the Thompson radius or classical radius of the electron.

 

The gravity and electrostatic equations just differ by the constant of proportionality don’t they? So the two systems ought to be analogous from a purely forces point of view, but as you know, there is the requirement that an accelerating charged particle radiates energy. I suppose you could think of the radiation requirement as analogous to a satellite experiencing drag from the top of the atmosphere and thus losing energy.

 

Isn’t it the case that the analogy used to be made but that it no longer is?  Electrons were thought of as point like “planets” orbiting a nucleus  (sun) with some extra rules to get around the holes in the analogy such as accelerating charges radiating energy.  The holes are rather important, so the key features are how the model had to be patched rather than the model itself. At which point why retain the model at all?  The solar system model will incorrectly have students thinking that the electron has a definite location around the nucleus rather than the more conceptually awkward probability associated with orbitals.

My memory has that the Bohr model only works for Hydrogen. I recall during my time at school and university being frequently told to forget what you had been previously taught. I enjoyed learning the new stuff so just accepted that this was how it had to be.  I’m now a much older dog that finds new tricks harder to learn and wonder about the value of learning that is likely to be discarded in the near future or otherwise never used again.

 

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