A current `i` flows along the length of an infinitely long, straight, thin-walled pipe. Then,
(a) the magnetic field at all points inside the pipe is the same, but not zero
(b) the magnetic field at any point inside the pipe is zero
(c) the magnetic field is zero only on the axis of the pipe
(d) the magnetic field is different at different points inside the pipe

Options

A. infinite
B. zero
C. `(mu_(0))/(4pi) . (2I)/r T`
D. `(2I)/r T`

Answer

B

Explanation

Let R be the radius of a long thin cylindrical shell.
To calculate the magnetic induction at a distance r (r < R) from the axis of cylinder, a circular shell of radius r is shown.
Since, no current is enclosed in the circle, so from Ampere’s circuital law, magnetic induction is zero at every point of circle. Hence, the magnetic induction at very point inside the infinitely long straight thin walled tube (cylindrical) is zero.