What is the magnetic flux?If the magnetic field caused by a magnet is B=15 webers/meters squared and the field linesgonormally through a Gaussian...

The definition of magnetic flux is the integral of the
magnetic field over a surface area.

F = int_surf (
B dot dS
)

In general, S can be any
oddly-shaped surface. In your problem statement, all of the flux lines are normal to the
surface. This means that you can visualize the answer to the problem by mapping
(stretching) the surface into a rectangle shape with surface area 20 cm^2. Just imagine
that all the field lines morph with the surface so that they remain normal, and the
field density remains 15 W/m^2.

Now, your
dealing with a geometry that is simple. B is constant, so take it out of the
integral:

F = B int_surf ( 1
dot dS ), where i is the unit
vector normal to the new surface. But, int_surf ( 1 dot
dS ) is just the area of the surface,
20cm^2.

Thus, F = 20 cm^2 * 15 Web/m^2 * 1 m^2 / ( 100 cm
)^2

F = 30
mWeb