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Name: Jeff H.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2001-2002


Question:
In introductory physics class, I was taught that some photons were not absorbed by electrons, but passed right through the atom. However, after reading a bit of Feynman, I get the impression that what actually goes on is that such photons are absorbed by the electron, but re-emitted, with the net effect of being the same as it was before it was absorbed. Is this a correct interpretation, and if so, is it the same photon which is re-emitted?


Replies:
Jeff,

Actually both events can occur. A photon entering the space of an atom has a certain probability of being absorbed. If absorbed, the time for which the photon energy is held depends on factors such as energy of the photon and structure of the atom. Most such photons are quickly released because they have an energy that is wrong for the atom. A quickly released photon is most likely to be emitted in a direction close to its original trajectory, but not always. Being released in a backward direction allows reflection to exist.

As for whether the released photon is the same, I would have to say no. For a moment, the energy and momentum of the photon are part of the atom. As the emitted photon usually has all the same attributes of the original one, there is often no difference between the two.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



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