Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Photons vs. electrons in excitation



Hi,

it is well known that the excitation of an electron in the ground
state (e.g. in hydrogen) requires a photon with a certain energy. The
energy must match with the energy difference between some excited state and
the ground state. If the incoming photon does not have the "right" energy
it does not cause excitation; instead, scattering takes place.

However, if the incoming particles are electrons with a certain
kinetic energy which does not match the energy difference between any
excited state and the ground state, they nevertheless cause excitation as
long as the electrons have enough energy to do so. Why is it so that the
bound electron is so "picky" with photons but when it comes to electrons,
anything goes as long as there is enough energy? This means that the
electron loses part of its kinetic energy in the interaction with the
atom and the "lost" energy appears in the excitation.

Regards,

Antti Savinainen
Finland