I am a high school student and I would like to know why in a magnetic field the Force, F, is equal to BIL x sin(theta), where theta represents the angle between the magnetic field and the current. I understand that F is proportional to B, I and L, but I do not understand the inclusion of sin (theta). In other words, I would like to see a simple proof or explanation of why the effective length of the wire is L x sin(theta)