Force on the wire (uniform magnetism)

Oct 2011
Hello, it's my first time here!

I'm taking physics in college and I went on a trip with my family and I got this problem I'm having trouble with. Help on how to get started?

A semi-circle piece of wire of radius R with current I is situated around the origin as shown below. What is the force on the wire if there is a uniform magnetic field everywhere and is pointing in the –z direction?

See the image by clicking here.

Thank you for your help!
Sep 2012
force on wire

The force will point along -x and the value is F=2R*i*B.
You can think that since the force is proportional to the cross product of the length elements along the wire with the field B,integrated along the wire, by symmetry only the projections os such elements along the y axis will contribute to the product. Since the projection is 2R we obtain the answer given above.