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So I've recently learned about photoelectric effect. It made sense at first, but when I try to combine it with what I thought I knew about emission and reflection of photon, things become rather messy.

My questions :

1)When photons interact with electrons, they can either be absorbed or reflected or pass right through. Is that correct?

2)When light photon excites an electron in the inner shell, it is absorbed. A photon is subsequently given off during de-excitation. Does the photon given off have the same energy as the photon absorbed earlier?

3)If the answer to the above question is "yes"(which is what I have been taught in school, though it's a struggle to reason it), then how is the process different from reflection? Say it absorbs light photon and then re-emits the exact same photon.

4)to add to question 2 and 3,how come in some cases, photons with shorter wavelengths are apparently radiated as photons with longer wavelength? (Earth absorbing uv but radiates it as infrared).

There are likely to be major mistakes in my understandings, which would explain why I can't seem to puzzle all these phenomena together... Any correction would be greatly appreciated!

Thank you.

Clara
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1 Answers1

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Photons when absorbed put the electron in a higher energy level (read Bohr orbits to understand this better). But high energy orbits are unstable as every system tends to minimize its energy. So the electron loses energy and returns to the ground state in less than 10^-8 s. Reflection is when a photon with the same energy (and correspondingly, the wavelength) as that of the absorbed one is emitted. This doesn't always happen.

It does not necessarily have to be the same energy as the photon absorbed. Let's say the electron was in n=1 before getting kicked into a higher orbit. Then it gets upped to n=3. The electron may transition from n=3 to 1 directly, emitting the same energy photon as was absorbed (more precisely, with energy equal to the energy difference between n=3 and n=1 levels). But it could also take a different path and go from n =3->2->1 emitting two photons as it finally reaches ground state, one in each successive transition.

cartilage
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