# Finding the E field with a changing p?

1. Feb 7, 2012

### swimforever

Finding the E field with a changing p???

Given that ρ=ρ0r/R when finding the charge enclosed would you use

1:Qencl = ∫(ρ*dV)

or

2: Qencl = ρV given that ρ has already been given with a coefficient to account for a changing r?

2. Feb 7, 2012

### CantileverMan

Re: Finding the E field with a changing p???

If you mean that little 'r' is a variable radius then you must integrate (option 1), because the charge density is a function of the radius.

Integrate over a volume if the problem is 3dimensional, or over an area if the problem is 2d.