Magnetic flux formula confusion

[sameeralord]

Hello everyone,

In the magnetic flux formula in our textbook it says Ø = BAcosø and somewhere else I saw it as Ø=BAsinø. I don't know which one to use. If F=BIL sinø
why does magnetic flux have cos in it formula. If something is perpendicular don't we have to use sine. Any help would be apppreciated. Thanks

 

[tuananh3ap]

formula \phi = BAcos\alpha is magnetic flux
it like \phi=\oint<b>E</b>d<b>A</b>
formula F=ILBsin\alpha was deduced from F=qvB or F=qvbsin\alpha

 

[Domenicaccio]

Hello everyone,

In the magnetic flux formula in our textbook it says Ø = BAcosø and somewhere else I saw it as Ø=BAsinø. I don't know which one to use. If F=BIL sinø
why does magnetic flux have cos in it formula. If something is perpendicular don't we have to use sine. Any help would be apppreciated. Thanks

Those 2 formulas might both be fine, it just depends on how is the angle ø defined.

They are however just special cases, when the area considered is flat and B is constant.

The real definition of magnetic flux, which is valid for every surface and in every case, is:

\Phi = \int_A B_n dA

which means that you have to sum (integral) the contributes of the perpendicular (normal) component of B in every point of the surface A.

When B is constant everywhere (does not vary in different points of the surface) and A is flat, the integral goes away and the normal component of B is Bcosø if ø is defined as the angle between B and an axis perpendicular to A (or Bsinø if ø if the angle between B and the surface A).

 

[sameeralord]

Those 2 formulas might both be fine, it just depends on how is the angle ø defined.

They are however just special cases, when the area considered is flat and B is constant.

The real definition of magnetic flux, which is valid for every surface and in every case, is:

\Phi = \int_A B_n dA

which means that you have to sum (integral) the contributes of the perpendicular (normal) component of B in every point of the surface A.

When B is constant everywhere (does not vary in different points of the surface) and A is flat, the integral goes away and the normal component of B is Bcosø if ø is defined as the angle between B and an axis perpendicular to A (or Bsinø if ø if the angle between B and the surface A).

I got it. You are right it depend on the angle they give. Thanks a lot .