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Radiation and quantised orbits

Question: Bohr rejected the Rutherford's model of atom by arguing that it contradicts the classical theory of electrodynamics which says that a revolving charge should radiate energy. But in his model, Bohr directly assumed that the orbits in which electrons revolve are NON RADIATING. According to him, the orbits are quantised, but then what happened to classical theory of electrodynamics?

Answer:

The problem here is that there are two distinct areas of physics. The classical one and the quantum mechanical one.
What goes on in the atom is essentially quantum mechanical. The laws of classical physics simply do not fully explain what is going on there.
Think of the electron in orbit, in a classical situation it is accelerating and will therefore radiate energy. However Bohr's theory forbids this unless there is a free space in an energy level below it as you know it cannot simply spiral inwards.

However in the quantum mechanical world we should think of it as being in a static stable state and therefore the word acceleration has no real meaning. Also if you consider the electron to be a wave function then any concept of acceleration is again not relevant.

So to summarise there is nothing wrong with the classical theory, in many situations, it is just
that it does not apply here.

 
 
 
© Keith Gibbs 2011