How do electrons and photons interact?

First, recall that electrons surround the nucleus of anatom, occupying different energy levels. To move from a lower to a higher energy level, an electron must gain energy. Oppositely, to move from a higher to a lower energy level, an electron must give up energy. In either case, the electron can only gain or release energy in discrete bundles.
Now let's consider a photon moving toward and interacting with a solid substance. One of three things can happen:
The substance absorbs the photon. This occurs when the photon gives up its energy to an electron located in the material. Armed with this extra energy, the electron is able to move to a higher energy level, while the photon disappears.
The substance reflects the photon. To do this, the photon gives up its energy to the material, but a photon of identical energy is emitted.
The substance allows the photon to pass through unchanged. Known as transmission, this happens because the photon doesn't interact with any electron and continues its journey until it interacts with another object.

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Apoorva Arora

IIT Roorkee

askIITians Faculty