# E-field calculations

1. Sep 20, 2007

### cscott

Can a hollow cylinder of known radius, height and charge be treated as a line of charge if one is trying to find the E-field at an arbitrary perpendicular distance from the center of the flat surface?

2. Sep 20, 2007

### Astronuc

Staff Emeritus
What flat surface? What does the flat surface have to do with the cylinder? Is the end of the cylinder?

Also has to do with the radius R in relation to the length L, and how close one is to the cylinder.

3. Sep 20, 2007

### genneth

Assuming that you mean on axis, away from the capped end of the cylinder, then no. But it is well approximated, in the case that the distance is far greater than the radius of the cylinder.

4. Sep 20, 2007

### cscott

yeah I mean on the end of the cylinder.

The test position is on the axis that goes through the hollow center of the cylinder

Last edited: Sep 20, 2007
5. Sep 20, 2007

### Astronuc

Staff Emeritus
Sphere?

Along the axis, if the distance if far enough away, one would approximate it as a point source.

Does anything here look like the geometry to which one is referring?

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gaulaw.html#c4

6. Sep 20, 2007

### cscott

I meant to say cylinder instead of sphere, sorry.

It's just like the 'conducting cylinder' geometry from your link except it's hollow; just a thin surface.

7. Sep 23, 2007

### cscott

If I have the expression for the E-field of a ring of charge at a perpendicular (to the plane of the ring) distance 'x' away from it's center can I just integrate with respect to 'x' over a distance (length of cylinder) to get the E-field for the hollow cylinder?