Questions about spherical conductor

[Niles]

Homework Statement

A charge Q is placed at the center of a conducting spherical shell of inner radius R1 and outer radius R2. The sphere has no net charge.

Ok, I have some statements for this setup. Would you be kind to check them?

The Attempt at a Solution

1) The electric field in a distance R < R1 from the pointcharge Q is the electric field coming from the charge itself.

2) The electric field in a distance R1 < R < R2 is zero (E-field zero inside a conductor always).

3) In a distance R > R2 the electric field is only coming from the point charge, since the conductor has no net charge.

4) The formula for the electric field outside a conductor: E = (sigma/epsilon_0)n. Does this only apply to the outside surface of a conductor, or also the inside surface? (In this case the inside-surface of the spherical shell)

 

[Astronuc]

If one puts a charge Q (assumed positive) in the center of a spherical 'conductor', what happens to the charges in the conductor (which if neutral, has a balance of - and + charges)?

 

[Niles]

The positive charges go to the outer surface and the negative charges go to the inner surface.

 

[Astronuc]

What can one say about the charge densities of the inner and outer surfaces?

 

[Niles]

Charge-density is the charge per area, and since the charge is the same with different sign, I guess the only thing that makes them vary is the area.

 

[reilly]

what's the definition of a conductor?
Regards,.
Reilly Atkinson

 

[Niles]

The electric field inside is zero?

Am I way off with my answers in #1?

 

[Redbelly98]

1, 2, and 3 look good to me. I'd have to think (more than I have time for at the moment!) about #4.