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I know that an atom has energy levels i.e the energy of each electron in the atom falls in a discrete energy level.

I am also aware that, if the exact difference of energy between two levels is provided to an electron, then it jumps to the higher energy level, and that is a lower amount of energy is provided, the electron stays where it is.

My questions are:

  • What happens to the energy in the second case? Does it get radiated back as heat? If not, where does that energy go?
  • What happens if more than the requisite amount of energy is provided? Does the electron stay where it is, or does it go to the higher energy level?
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If the energy exceeds the minimum needed, there are a few possibilities:

  • More than one electron may be affected.

  • The electron(s) can be moved to yet higher levels within the atom.

  • The electron can be expelled (raised to a very high level) with the electron(s)' kinetic energy making up the difference.

  • At sufficiently high energy, pair production can occur.

  • Also, rather than expending all its energy on the electron, the photon can be scattered as a lower frequency (less energetic) particle (since it interacted at a point, I'd consider it a particle for that duration).

So -- the excess energy, in effect, can be shared between the photon and electron in varying proportions.

If less than the minimum amount to raise the electron's level is supplied, then the electron stays put... except for quantum phenomena such as tunneling. The Esaki diode exhibits negative resistance, where electrons are more likely to pass through the p/n junction with lower bias.

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