Magnetic Effect of Electric Current

Question

A cylindrical wire of radius R is carrying current i uniformly distributed over its cross-section. If a circular loop of radius ' r ' is taken as amperian loop, then the variation value of ∮B.dl over this loop with radius ' r ' of loop will be best represented by:

Answer 1

The correct answer will be option (B)

Comments

For a current carrying cylindrical wire B=0 from r=0 to r=R. So how can It be option (B)