# Homework Help: Finding Electric Flux

1. Jan 23, 2007

### Physicus2

1. The problem statement, all variables and given/known data
"Given a constant electric field E = E(subscript 0)(1 / square root of 2 i + 1 / square root of 2 k), find the electric flux through a circular disk of radius a lying flat in the x-y plane. Orient the disk so that the positive direction is toward positive z.

2. Relevant equations

The most relevant equation to this problem is Eflux = integral of E dot dA.

3. The attempt at a solution

I've completely finished a solution, but there are many places to make mistakes here, I think, despite what may be a simple problem.

I said that Eflux = (-E subscript 0) double integral from 0 to a (x and y) of E dot k dx dy. I went on to place 1 / square root of 2 into the integral, but only once for the k and not the i component. Would this be correct? I then integrated with respect to x and got (1 / square root of 2)x dy. Integrating again, I think I get (1 / square root of 2)a^2. Note that i replaced x with a there. I'm unsure if I did my double integral correctly...I'm only beginning Calculus 3 now, and it wasn't a prerequisite for Physics. Oh well.

When all is said and done, I get -E(subscript 0) a^2 / square root of 2.

Is my answer close? I presumed that E is negative because the disk was in the positive Z direction. I apologize for the fact that I'm unable to upload images of my work. Any help would be very much appreciated!

2. Jan 23, 2007

### mukundpa

Is the field is uniform?

if no then think of integration.

if yes, no need of integration simply write field and the area as vectors and perform dot product of them.