Why Is It Sin Theta Instead of Cos Theta in Magnetic Flux Calculation?

[watthappening]

Homework Statement

I had know that for finding magnetic flux is NBA cos theta. The answer is C though, so why is it sin theta instead of cos theta? I wonder

Homework Equations

BA cos theta
NBA cos theta[/B]

The Attempt at a Solution

 

[gneill]

This is the problem with memorizing formulas without making sure you know what the variables represent. Try to find in your notes or textbook where that formula was defined and see how the angle θ is defined there.

 

[watthappening]

This is the problem with memorizing formulas without making sure you know what the variables represent. Try to find in your notes or textbook where that formula was defined and see how the angle θ is defined there.

I did know what the variables represent, the angle is between the normal of the area of the surface and magnetic field lines. But i still didnt get the reason.

 

[gneill]

I did know what the variables represent, the angle is between the normal of the area of the surface and magnetic field lines. But i still didnt get the reason.

Okay, the angle in the given diagram does not subtend the area normal and the magnetic field direction. How does this given angle relate to the angle used in the definition? (It may help to use a little triangle geometry)

 

[watthappening]

Okay, the angle in the given diagram does not subtend the area normal and the magnetic field direction. How does this given angle relate to the angle used in the definition? (It may help to use a little triangle geometry)

It's doesnt? oh well, I didnt know that

 

[gneill]

It's doesnt? oh well, I didnt know that

The required area normal is perpendicular to the area of the coil "face", that is, it's perpendicular to the plane of the coil. The angle shown in the diagram subtends the magnetic field and the plane of the coil itself.

 

[watthappening]

The required area normal is perpendicular to the area of the coil "face", that is, it's perpendicular to the plane of the coil. The angle shown in the diagram subtends the magnetic field and the plane of the coil itself.

is this correct?

 

[gneill]

Sure. That'll work. You should be able to see the relationship between the θ given in the problem figure to the one you've just drawn in.

 

[watthappening]

Sure. That'll work. You should be able to see the relationship between the θ given in the problem figure to the one you've just drawn in.

alright thanks for the help, mate