# Uniformly Charged Circular Disk

1. Oct 11, 2012

### cheungw

1. The problem statement, all variables and given/known data
In what direction (using cylindrical coordinates) around a uniformly disk does the electric field NOT point?

2. Relevant equations
The directions could be r, θ, or z.

3. The attempt at a solution
I don't think it can point in the θ or the z direction-- either one would imply that there is a built-in preference to space for a certain direction, because symmetry arguments say that these two directions should be treated equally in all directions.

I'm not sure though-- I'm assuming they mean around the edge of the disk on the outside, is this correct?

2. Oct 12, 2012

### SammyS

Staff Emeritus
Hello cheungw. Welcome to PF !

What if they don't mean around the edge of the disk ?

What if they mean in the vicinity of the disk ?

3. Oct 12, 2012

### Ned Stark

The problem says "around" the disk, so that probably means where does E not point outside of the disk.

to answer, consider the electric field in regions far far away from the disk, so that the disk appears to be a point. What would the field look like?