Fields and Forces

[MLI]

Does anybody know when there is a uniform field acting normally to the plane of paper, why do we consider the field as a magnetic field not an electric??? and how could we reference to the circular motion in order to justify the answer?? also can anybody explain this formula or at least its symbols r= (mv)/(Bq)

Thanks

[Beni]

Not sure what you're asking for in the first part :/

As to the formula,

r=radius; m=mass ; v=instantaneous velocity ; B=magnetic field; q=charge

The way I understood it (did it this week in class) was that it is derived from Lorentz Force

We start out with

F=q(VxB) (where bold signifies a vector and x a cross product)

But since V⊥B (cross product of perpendicular vectors: V*B*sin 90=V*B)

we get F=q (V x B)

Now use Newton's second law F=ma and substitute a for v²/r,

thus giving mv²/r=qVB

and after dividing by V and arranging a bit

r= (mv)/(Bq)

Hope I could help and someone please correct me if I am wrong!