# Applying Gauss' Law to find Electric Field

I'm in doubt in the application of Gauss' Law to find electric fields when the charge distribution is symmetric. Well, first of all: I know how to find the magnitude of the field - we just enclose the charge distribution with a gaussian surface on which the electric field will not change it's magnitude, and then using Gauss's Law we can write it in terms of the total charge inside and the area of the gaussian surface.

My problem is: how do I find the direction of the field? I mean, in a spherical symmetric distribution it's easy, because we know what's the vector that points radially outwards (it's simply one of the unit vectors from spherical coordinates). But what about a cylindrical symmetric distribution ? Would I need to use the unit position vector of cylindric coordinates ?

In the general case I would need to switch to more appropriate coordinates to write the field ? Is there a general way of treating this ?

Sorry if this question is to silly or too basic. I'm just trying to understand how to use properly this law.

• Use it in its proper, vector form, that should give you the vector field, not just the magnitude! – user20250 Mar 21 '13 at 20:54