A long, thin hollow conducting cylindrical pipe with the radius of R carries uniformly distributed current I, directed into the page.

A long, thin hollow conducting cylindrical pipe with the radius of R carries uniformly distributed current I, directed into the page. A long thin wire, coaxial with the pipe, carries current I directed out of the page. What is the magnitude of the magnetic field at a point distance r away from the center of the pipe, if r<R ?

a. 0

b. UoI/2pi r

c. UoI/ 2pi R

d. UoI/2pi ( 1/R - 1/r)