# Homework Help: Can I use Gauss' Law for this?

1. Feb 7, 2016

### Taulant Sholla

1. The problem statement, all variables and given/known data

2. Relevant equations
Gauss' Law: ∫E⋅da = qenc0
E-field: E = kq/r2

3. The attempt at a solution
I solved this using electric field equation, differential elements, and integration. The correct answer is, I think, E=-q/(8πε0R2)

QUESTION: Can this be done via Gauss' Law? The source charge itself is a "cup surface." Here's my attempt...

2. Feb 7, 2016

### BvU

And which way is that $\vec E$ pointing ? What is the $R$ there ?

The E you calculate using Gauss law, is it the same everywhere ? Pointing which way ?

3. Feb 7, 2016

### SammyS

Staff Emeritus
I know of no way to use Gauss's Law to solve for E at the center. There's not the required symmetry.

What are the requirements for using Gauss's Law for such a purpose?

4. Feb 7, 2016

### Taulant Sholla

There are no requirements to use Gauss' Law. I was wondering if it is possible. I assume since the source charge is asymmetrical, Gauss' Law can't be applied?

5. Feb 7, 2016

### SammyS

Staff Emeritus
If you're calculating flux from knowledge of the charge distribution, or vice versa, then you're correct.

However, if you use it to get the field from the charge distribution, there are requirements, involving symmetry, as well as the Gaussian surface which takes advantage of that symmetry.

6. Feb 7, 2016

### Taulant Sholla

okay, thank you very much!