Question

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

• A. the magnetic field is zero only on the axis of the pipe
• B. the magnetic field is different at different points inside the pipe
• C. the magnetic field at any point inside the pipe is zero
• D. the magnetic field at all points inside the pipe is the same, but not zero

Answer 1

Answer: (C)

the magnetic field at any point inside the pipe is zero

Using Ampere's law, $\oint Bdl={\mu }_o{I}_{en}$ the magnetic field inside the pipe is zero because it enclose no current i.e $I_{en}=0$.