# Net electric flux help?

1. May 8, 2013

### asdf12312

1. The problem statement, all variables and given/known data
The charge distribution in the figure to the right is a cylindrical solid of charge q, radius R, and length H. The Gaussian surface S is a cylindrical shell with radius r and length h, with r > R. Determine the net electric flux given that q = 12Q, R = 5L, H = 6L, r does not apply, and h = 3L (type the integer value, along with the sign, without typing units Q/e0):

2. Relevant equations
"The net electric flux will be in units of Q/e0, with e0 the permittivity of free space."
e0=8.85x10^-12

3. The attempt at a solution
have no idea how to do this. I tried q/e0 = 12/(8.85x10^-12) but its too huge value..maybe i got the wrong equation.

edit; i just got this. turns out you didn't need ANY equations at all, just common sense. its just q*(h/H) which in this case is 6 though I have no idea why this is the answer, it would just give you the enclosed charge right? you would still have to divide by e0..?

Last edited: May 8, 2013
2. May 8, 2013

### rude man

Yes the net charge inside the Gaussian surface is qh/H but substitute q = 12Q and then ε0*(electric flux) = qh/H. The answer thus is electric flux = 12Qh/Hε0 but the answer is to be in units of Q/ε0 so what is the answer then? Does it help if I rewrite flux = (12h/H)(Q/ε0)?