Question

A long, cylindrical tube of inner and outer radii a and b carries a current i distributed uniformly over its cross-section. Find the magnitude of the magnetic field at a point (a) just inside the tube (b) just outside the tube.

Answer 1

(a) At a point just inside the tube the current enclosed in the closed surface = 0.

Thus B = μ₀O/A

(b) Taking a cylindrical surface just out side the tube, from ampere’s law.