Electric field near conducting shell

[lys04]

Homework Statement

Electric field near conducting shell

Relevant Equations

E=kQ/r^2

How would I do this question? I am having trouble figuring out what the radius is meant to be, why is it not 3R?

 

[PeroK]

The charge is inside a conducting shell. What is the relevance of that?

 

[lys04]

The charge is inside a conducting shell. What is the relevance of that?

Induces a charge in the inner surface of the shell?

 

[PeroK]

Induces a charge in the inner surface of the shell?

Have you studied that? Or, learned any techniques to find the electric field outside an asymmetric charge configuration?

 

[lys04]

Have you studied that? Or, learned any techniques to find the electric field outside an asymmetric charge configuration?

I've learnt Gauss's law, if that's applicable.

 

[PeroK]

I've learnt Gauss's law, if that's applicable.

Gauss's law is useful. What can you say about the potential on the surface of a conductor?

 

[BvU]

I've learnt Gauss's law, if that's applicable.

In a way: you will have to argue why the required symmetry (*) is present.

Spoiler: (*)

spherical symmetry of the field outside the shell

$\$

 

[lys04]

Gauss's law is useful. What can you say about the potential on the surface of a conductor?

It's uniform?

 

[lys04]

In a way: you will have to argue why the required symmetry (*) is present.

Spoiler: (*)

spherical symmetry of the field outside the shell

$\$

Yeah I'm not sure about that

 

[PeroK]

It's uniform?

Yes. The surface of the shell must be an equipotential. Now, the potential is fully determined by the boundary conditions (technically this is a uniqueness property of electrostatic solutions). You know that outside the shell a spherically symmetric potential is a solution, so it must be the only solution.

Now, you can apply Gauss's law.