An electric current flows along the length of a hollow tube, distributed uniformly over its surface. The magnetic field

Step-by-step solution

By Ampere's circuital law, B d l = ₀ I_ enclosed . For any point inside the hollow tube at a distance r from the axis ( r B(2 r) = 0 B = 0 Thus, the magnetic field is zero at all points inside the tube, including the axis. Since it is zero everywhere inside, it remains constant. For a point outside the tube ( r > R ), the enclosed current is the total current I . B(2 r) = ₀ I B = ₀ I 2 r Thus, the magnetic field is non-zero immediately outside the tube and decreases as 1 r .