As for your first question, I would guess that it would depend on how the ions/atoms are bonded as to whether or not it is the original electron that travels to the PI. For instance, if the atoms in between NI and PI are conductive, they will have a conduction band of valence electrons that...
Homework Statement
The problem is: Consider a tunnel that connects any two points A and B on the spherical Earth (assuming constant density). The tunnel is a vacuum, and the train traveling through the tunnel is traveling on a frictionless track with no engine (i.e. it is just falling through...