# Conducting cylinder and wire

1. Mar 6, 2005

### Gale

An infinitely lond cylindrical conductor of inner radius "a" and outer radius "b" initially has a positive surface charge density of
$$\sigma_{o}$$
on its outer surface. A wire of positive charge per unit length
$$\lambda$$
is then placed on the axis of the cylinder. Find the final surface charge densities on its inner and outer surfaces.

So thats the problem. I wasn't really sure how to start. I got the formula for electric feild caused by a straight line charge.
$$E=\frac{2k\lambda}{r}$$
but then i wasn't really sure what to do with that... so could someone give me a push in the right direction. Thanks..

gale~

Last edited: Mar 6, 2005
2. Mar 6, 2005

### StatusX

The charge inside the conductor has to be 0. Calculate what uniform surface charge has to be placed on the inner surface to make this so, and then use the fact that the total charge on the conductor is conserved to find the outer charge. Everything will be uniform because of the symmetry of the problem.

3. Mar 6, 2005

### Gale

right ok... that makes sense... kinda... think you could maybe set me up a formula or two to work with... i've got sort of limited resources (my class notes contain more doodles than actual physics) and how do i involve the wire?

Last edited: Mar 6, 2005