Homework Help: Flux - simple integral computation

1. Oct 6, 2009

quantum13

1. The problem statement, all variables and given/known data
A surface has the area vector A = 2i + 3j. What is the flux of a uniform electric field through it if the field is E = 4i?

2. Relevant equations
Integral calculus, vectors

3. The attempt at a solution
I don't understand why one could do this. The integral is of E and dA, not E and A. How can I use A to determine dA?

This is a crackpot way I thought of

$$\Phi = \int \vec{E} \cdot \vec{dA}$$

$$\Phi = \vec{E} \cdot \int \vec{dA}$$

$$\Phi = \vec{E} \cdot \vec{A}$$

Then Phi = 4i dot (2i + 3j) = 8 flux units

This seems like wild fantasy though as I don't know if I can pull out a constant from a dot product integral

2. Oct 6, 2009

kuruman

There is no dA to speak of. You are given A which is the same everywhere and E which is uniform. Just take the dot product as you have in your third equation. There isn't much to this problem/