# Homework Help: E.M , capacity of a conductor?

1. Feb 8, 2006

### ghosts_cloak

Hello guys, well its that time of the week when Im busy working on my homework again!
One of this weeks questions is that there are 2 hollow concentric conducting spheres which hold charges Q1 (inner shell, radius R1), and Q2 (outer shell, Radius R2 )

1) Find the potential difference between them. I think this is (Q2-Q1)/4*Pi*E0*r ?

2)If q1 is +ive, and a wire connection is made from inner to outer conductor, charge will flow. How does direction of flow depend upon the magnitude and sign of Q2?

I think charge will flow from higher to lower potential, ie if Q2 is a smaller +ive charge, charge will flow from q1 to q2.
Is negative charge a lower potential than a positive, I guess?

But this next part really gets me: What is the capacity of the above pair of conductors? (Answer 4*Pi*E0*R1R2/(R2-R1) )

What on earth does "capacity" mean, we havent come across that term before! I would appreciate a poke in the right direction for this! There is another part but I havent tried that yet so I wont post here.

Any help and hints (but no solutions please it is assesed) are most appreciated :-)

Thank you

~Gareth

2. Feb 8, 2006

### quasar987

Error: r not defined.

What is the potential at the surface of shell 1? Of shell 2?

3. Feb 8, 2006

### ghosts_cloak

Hi :-)
Oh I see, r should actually be R2-R1 in the equation I posted for the potential difference?

Thanks,

Gareth

4. Feb 9, 2006

### quasar987

Yes.
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