A current i amp flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is

Let R be the radius of a long thin cylindrical shell as shown in fig. In order to calculate the magneticinduction at a distance r(r< R) from the axis of the cylinder, a circular shell of radius r is shown in fig. There is no current enclosed in the circle Therefore, from Ampere's circuital law, ma8tretic induction at every point of circle in zero. Hence, the magnetic induction at any point inside a long straight thin walled tube (cylindrical) is zero