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Revolution of electron and that of the planets

  1. Jan 31, 2012 #1
    planets do not loose energy when they orbit the sun due to interplay of centripetal and centrifugal force. Then why is this system not able to explain that electrons do not loose energy while orbiting the nucleus?
  2. jcsd
  3. Jan 31, 2012 #2


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    Hi Aakash! :smile:
    The problem is that an accelerating charge emits electromagnetic radiation (and therefore loses energy).

    (this is easy to prove, and has nothing to do with quantum theory).

    So a planet with a net charge would lose energy. :wink:
  4. Jan 31, 2012 #3


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    Electrons also do not orbit the nucleus. This is Rutherford's antiquated view of the atom that has since been replaced by the understanding that electrons exist in "clouds" determined by their wavefunctions.
  5. Jan 31, 2012 #4
    thank you
  6. Jan 31, 2012 #5
    In fact a planet orbiting a star does lose energy, albeit extremely slowly, to gravitational radiation. This is very closely analogous to the way an orbiting charge loses energy to electromagnetic radiation. But gravity is a very weak force, so energy losses due to gravitational radiation are unmeasurably small except in special cases.

    In both cases, the point is that while centripetal and centrifugal forces do balance out, there is another force acting on the orbiting body. The radiation it emits "pushes back" on it, so there is a drag force that slows the body down and causes it to spiral inward.

    To explain why this doesn't happen to electrons in atoms we need quantum mechanics.
  7. Jan 31, 2012 #6

    Not really. According to Newton's first law - "The velocity of a body remains constant unless the body is acted upon by an external force", i.e. in the abscence of such, it remains in motion. Then come the centripetal and centrifugal forces.

    Your example is a very bad analogy, but i'd say they don't lose energy because they are not really in motion. Lots of stuff at the micro scale is motion-like, real-like, spinning-like, etc. -like(but not quite so in reality).
  8. Jan 31, 2012 #7


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    In GR, frame dragging induces orbital instability.
  9. Feb 1, 2012 #8
  10. Feb 1, 2012 #9

    D H

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    One problem with that: Newton's laws are not (exactly) correct. They are instead approximately correct in a limited regime velocities that are very, very low compared to the speed of light, distances that are very, very large compared to the Schwarzschild radius.

    The_Duck in post #5 was referring to one of the predicted effects of general relativity. Gravitational radiation is immeasurably small in the case of the planets orbits about the Sun. The effect is not so small in the case of two very massive object orbiting very close to one another. It has in fact been observed. The observations eventually led to the discoverers receiving the 1993 Nobel Prize in physics.
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