Q:

Electrons motion

Some days ago, I was reading a very simple text about photoelectric phenomenon (at high school level) that this question came to mind.  How do electrons move (for example during their translation from cathode to anode in photoelectric phenomenon)?  Is motion of an electron pure translation or electron rotates about its axis (if it is a tiny sphere) and translates simultaneously (like the earth motion)?  In other words, what is an electron kinetic energy?  Is it equal to $\large{\frac 12}m_ev_e^2$ or $\large{\frac 12}m_ev_e^2+\large{\frac 12}I\omega ^2$? 

A:

The electron energy (the portion that changes at least) will be mainly due to kinetic energy (translational) and potential energy due to the potential difference between the cathode and the anode.   
The electron does have a "spin", but this spin isn't like that of a spinning sphere.  The reason for the name spin is simply that the electron spin describes the angular momentum of the electron, similar to how a rotating sphere has a angular momentum.  In fact all electrons have the same spin value, and can't be "spun" faster or slower. 
In this case, you could think of the electron as a wave.  And the frequency of the wave would change as the speed changes.  The frequency is related to the momentum, which is related to kinetic energy and more.