# Find the flux through a surface S (Electromagnetic Theory)

1. Sep 12, 2011

### jajay504

1. The problem statement, all variables and given/known data
A point charge q1 is located on the y-axis at r1= a (Y_hat) and another q2 located at the mirror point r2= -a (Y_hat). The charges are not necessarily the same sign or magnitude. Now consider the circular surface S of radius a contained in the x-z plane through the origin. Take the normal vector to this surface to point along the positive y-axis.

a.) Find the flux of the electric field through S.
b.) Use Mathematica to plot the field lines in the y-z plane through the origin for the following three cases: q2=-10q1, q2=q1, and q2=10q1.

2. Relevant equations

I have no idea how to start this problem or how to plug it into mathematica

3. The attempt at a solution

2. Sep 12, 2011

### vela

Staff Emeritus
You need to show some effort at trying to solve the problem yourself before receiving help. This is pretty basic stuff. What's the field of a point charge? What's the definition of flux?

3. Sep 12, 2011

### jajay504

Flux= EA cos(theta)= E.A
I got flux = q/4e0

I don't have experience using mathematica at all

4. Sep 12, 2011

### jajay504

Sorry for that. This one. I think I may have over thought it a bit.

5. Sep 12, 2011

### vela

Staff Emeritus
That only works for a constant electric field.
How did you get this? What's q? The original problem has q1 and q2.