General questions about conductors in electrostatics

[channel1]

These are just some general questions I have about what I'm reading in my physics book. I'm really having trouble visualizing what happens to electrons in conductors (this is all for electrostatics btw).

Three scenarios:

(1) A solid conductor
Why is the charge only on the surface of the conductor in electrostatics? (I understand that electrostatics means that the electrons can't have a net-motion so the E-field has to be zero, but how do all the charges come to pile up on the outside of the conductor? Wouldn't all the like-charges repel each other? My book shows a diagram with a bunch of positive charges along the outside of the conductor.)

(2) A conductor with an empty cavity(3) A conductor with a cavity and a charge in the center of the cavity
For instance, a positive charge q in the center will result in a charge q+q_c on the surface of the conductor (where q_c is the original charge of the conductor without the cavity or charge in the center). Why? The diagram also shows that the surface of the cavity has a charge -q, but where does the -q come from physically if all we've added to the system is the +q charge?

 

[jbsteele]

1) In a solid conductor, the electrons are free to move around and rearrange themselves in response to any electric fields. As the electric field increases, so does the repulsion between electrons, which causes them to move away from the source of the field. As they move away, they leave behind positive charges on the surface of the conductor (due to the lack of electrons). This is why you see a bunch of positive charges along the outside of the conductor - this is because of the build-up of positive charge on the surface due to the movement of electrons away from the source of the electric field. 2) When a cavity is present in a conductor, the electrons will be repelled from the sides of the cavity and accumulate on the walls of the cavity, creating an electric field that will oppose the external electric field. The net effect is that the electric field inside the cavity will be reduced, resulting in a lower potential energy compared to the conductor without the cavity. 3) When a charge is placed in the center of the cavity, the electric field will be further reduced since the charge will create an additional electric field that opposes the external electric field. This will result in a redistribution of charge, with the surface of the conductor having a charge of q+q_c where q_c is the original charge of the conductor without the cavity or charge in the center. The surface of the cavity will have a charge of -q, since the electric field created by the charge q in the center will attract electrons to the surface of the cavity, leaving a net negative charge.