I had this statement in my physics textbook
Photoelectric effect is seen only when electrons are bound, because free electrons cannot absorb the whole energy of the photon while conserving momentum and energy.
I found a simple proof for this statement here.
However, the proof states in the beginning itself, that
If the electron is bound to an atom then the atom itself is able to act as a third body repository of energy and momentum
Here's my issue: I've also read that "free electrons" are the loosely bound electrons of an atom, also called the conduction electrons.
If that is the case, then the statement in by book should be wrong, because if the free electrons were to be defined as loosely bound electrons, then it would be possible for them to absorb the whole energy of the photons. In fact, photoelectric effect is generally defined as the emission of the loosely bound electrons from a metal surface when light is incident on it.
On the other hand, though, if we consider that "free electrons" refers to isolated electrons, i.e. when there is no repository in the form of an atom, then the statement seems perfectly fine.
So my question is:
Does the definition of "free electron" depend on the context?
- If yes, then how do we determine which of the definitions is being referred to?
P.S. Wikipedia does say that the definition depends on the context. So the question now boils down to (2) only.