Gaussian Surface Electric Field Problem

[wompkins]

Homework Statement

An uncharged spherical thin metallic shell has a point charge q at its center. Find expressions for the electric field

1. Inside the shell
2. Outside the shell
3. has the shell any effect on the field due to q?
4. has the presence of q any effect on the shell?
5. if a second point charge is held outside the shell, does this outside chage feel a force
6. does the inside charge feel a force?
7. what is the apparent contradiction to Newton's 3rd Law
8. What is the resolution to the apparent contradiction?

Homework Equations

∫E*dA = Q/ε_0 where Q is net enclosed charge

The Attempt at a Solution

1. E-field inside metallic shell is 0
2. Outside it is like that of a point charge E = kQ/4πε_0
3. Yes the shell "shields" the field inside the shell to zero but outside acts like a normal E-field
4. It will polarize the metallic shell creating the E-field from the surface of the shell
5. Yes it will feel a force and it will be equal to qE where q is the second charge outside the shell and E is from part 2
6. The inside force will NOT feel a force, otherwise it would move
7. How can one feel a force but the other can't is the contradiction
8. The fact that the metallic shell "shields" the charge and get polarized by both charges allows the inner charge to feel no force

I feel like I get the first 3 parts, but 4-8 are just my intuition and was wondering if it was correct train of thought. If not just give me a hint in the right directions please!

 

[ehild]

Homework Statement

An uncharged spherical thin metallic shell has a point charge q at its center. Find expressions for the electric field

1. Inside the shell
2. Outside the shell
3. has the shell any effect on the field due to q?
4. has the presence of q any effect on the shell?
5. if a second point charge is held outside the shell, does this outside chage feel a force
6. does the inside charge feel a force?
7. what is the apparent contradiction to Newton's 3rd Law
8. What is the resolution to the apparent contradiction?

Homework Equations

∫E*dA = Q/ε_0 where Q is net enclosed charge

The Attempt at a Solution

[1]E-field inside metallic shell is 0

Wrong. Surround the central charge with a concentric sphere of radius r less then the radius of the metal sphere. What is the electric field at r?

[2]Outside it is like that of a point charge E = kQ/4πε_0
[3]Yes the shell "shields" the field inside the shell to zero but outside acts like a normal E-field

It shields the central charge from outside fields, but not from its own field.

[4]It will polarize the metallic shell creating the E-field from the surface of the shell

[5]Yes it will feel a force and it will be equal to qE where q is the second charge outside the shell and E is from part 2
[6]The inside [STRIKE]force[/STRIKE] charge will NOT feel a force, otherwise it would move
[7]How can one feel a force but the other can't is the contradiction
[8]The fact that the metallic shell "shields" the charge and get polarized by both charges allows the inner charge to feel no force


I feel like I get the first 3 parts, but 4-8 are just my intuition and was wondering if it was correct train of thought. If not just give me a hint in the right directions please![/QUOTE]