A current ` I` flows along the length of an infinitely long, straight , thin - walled pipe. Then

Options

A. the magnetic field at all points inside the pipe is 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

Answer

B

Explanation

Consider an Amperian loop inside a pipe. No current is enclosed by this loop as current only flows through the thin wall.

As `oint vecB.dvecl=mu_0xx` current enclosed by the amperian loop
`oint vecB.dvecl=mu_0xx0=0`
`vecB=0`
Choice (b) is correct.