# Flux integral help

## Homework Statement

Well, I'm trying to take advance in my course and learn about how to calculate flux integrals. I have a few problems I can try out but I can't seem to understand the method they are using to solve the problems.

## Homework Equations

I don't know..

All I have is int(surface) v x dA

## The Attempt at a Solution

For example, I tried doing one of the problems. The question asks me to find the flux of the vectorial field through the surface.

F = yj through the square of sides 4 in the plane y=5. The square is centered on the y axis, its sides are parallel to the axis' and is oriented in the positive y direction.

Now I was trying to figure out some sort of method of how to solve problems like these.

This is what I did. I replaced y=5 in the equation F=yj and then multiplied it by the orientation which gave me F = 5. In this case, my dA was jdxdy.

From there, I had a double integral such as int(0,4) int(0,4) F x dA.

int(0,4) int(0,4) 5dxdz = 80

That does give me the correct answer but I want to know if the way I got to it is correct. If its not, are there any equations or other information that I should know about. None are given in the book :(.

Thanks!