Question

A nonuniform magnetic field exerts a net force on a current loop ofradius R. The figure shows a magnetic field that is diverging fromthe end of the bar magnet. The magnetic field at the position ofthe current loop makes an angle θ with respect to thevertical.



a) Find an expression for the net magnetic force on thecurrent.
b)Calculate the force if R=2.0cm, I =0.50A, B=200mT, and θ=20degrees

Answer 1

For your first question we know that

F=BILsinθ

where B is mag field

I is current

L is length

Therefore to isolate I you get

I=F/BLsinθ

To solve for force plug these numbers in to thisequation

Recognize that you have to convert mT to T for magnetic fieldand also convert radius to m and times by two in order to getheight.

After doing this solve

F=.200 x .50 x .04 x sin20= .00136 N

Answer 2

Basically what john316, except to get the right answer I had tomultiply both parts by π.

A) F=B*L*I*sin(θ) but L=2πR
so for the final on part A you should getF=B*2*π*R*I*sin(θ)

B) For part B, just plug and chug.

Answer 3

But why is it 2ΠR if they tell you the length is 2R?  Why are we using the circumference instead of using its given length?