## College Physics (4th Edition)

We would also need to know the angle $\theta$ between the direction of the magnetic field and the surface area in order to calculate the average magnetic field through the surface.
$\Phi = B~A~cos~\theta$ Although we know the magnetic flux and the area, we would also need to know the angle $\theta$ between the direction of the magnetic field and the surface area in order to calculate the average magnetic field through the surface.