# Homework Help: Magnetic flux

1. Sep 2, 2010

### pat666

1. The problem statement, all variables and given/known data
A 2.6T magnetic field makes a 30 degree angle with a square loop 26cm on a side.

2. Relevant equations

phi=BAcos(theta)

3. The attempt at a solution
this should be a very simple question.
phi=2.6*.26^2cos30
phi=0.15Wb
mastering physics says this is wrong but I cant see any reason why????? should it be negative or something?
thanks for any help/

2. Sep 2, 2010

### ehild

Does this mean that the magnetic field encloses 30 degree with the plane of the loop? In the formula for the flux, you have to use the angle with respect to the normal of the plane.

ehild

3. Sep 2, 2010

### pat666

so how do I find theta ??? or would it be 90 degrees making the flux 0?

4. Sep 2, 2010

### ehild

The flux is maximum if the magnetic field is normal to the plane and 0 if the field is parallel to the plane.

ehild

5. Sep 2, 2010

### pat666

I still dont know what the angle should be though, why is 30 degrees not working?

6. Sep 2, 2010

### ehild

30° might mean the angle the field encloses with the plane, but you need the angle between the field and the normal of the plane. If a vector makes an angle alpha with a plane than it encloses (90°-alpha) with the normal.
And yes, theta=90° would make the flux 0 as the field is parallel to the plane and would not cross it.

ehild

7. Sep 2, 2010

### pat666

so the angle I should use is 60 degrees?

8. Sep 2, 2010

Try.

ehild

9. Sep 2, 2010

### pat666

Yeah that did it, thanks a lot ehild.