Historical qustion-models of atoms

  • Thread starter Bassalisk
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  • #1
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Main Question or Discussion Point

Hello,

I am apprentice in quantum physics and physics generally. When Rutherford posted his model, he was strongly negated because of the fact that electrons will fall in nucleus. Well i got that part quiet well but when i learned that planet goes around its sun mainly because inertia (losing very small fraction to surroundings) and finally grasped the concept of circular motion, it struck me. I am puzzled here, why they didn't assume that electron has inertia too or something. If electron would collapse to nucleus why wouldn't earth collapse to sun? Coulumb's force=gravity imo.

I am probably getting some concepts here wrong, but i cannot find consist answer anywhere about earths revolution.

Can u correct me and try to answer my question?

Thank you.
 

Answers and Replies

  • #2
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A body that is set in motion in an attractive potential field (like a gravitational field or an electric field) can indeed be put into a stable orbit that will never fall into the center of the field. Electric fields and gravitational fields are described by the same equation (the inverse square law), so at first glance, they would appear to lead to exactly the same behavior.

The difference is that the electron is charged. By Rutherford's time, enough was understood about electrodynamics to know that any electric charge which is accelerated will emit radiation (the technical term for this is Bremsstrahlung.) Remember that acceleration can mean a change in speed or a change in direction. The electron is always travelling at the same speed, but since it's in a circular orbit, it is always changing direction. Therefore, according to the laws of electrodynamics, it should constantly be radiating energy. If it were, this would gradually slow down the electron, breaking its stable orbit and causing it to eventually fall into the nucleus. This is the reason that scientists were skeptical of the orbit model of the electron.

Incidentally, the same thing would happen to a planet in a gravitational field, except that a planet is electrically neutral, so there is no radiation generated.
 
  • #3
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Thank you, things are much more clear now. But, this concept of electron emitting energy by having acceleration, he emits energy in form of photon right? and this energy would be "drawn" from kinetic energy from a electron, which is 1/2mv^2, thus in a spiral fashion collapsing into nucleus.

Am i getting this right?
 
  • #4
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Exactly. Conservation of energy dictates that if the electron emits a photon with some amount of energy, that energy has to come from somewhere, so it is drawn from the electron's kinetic energy, which slows it down. This is why it is called "Bremsstrahlung"--that word is German for "braking radiation".
 
  • #5
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exactly. Conservation of energy dictates that if the electron emits a photon with some amount of energy, that energy has to come from somewhere, so it is drawn from the electron's kinetic energy, which slows it down. This is why it is called "bremsstrahlung"--that word is german for "braking radiation".
thank you very much !!!!!!!!!!
 

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