Question

A current I flows along the length of an infinitely long, straight and 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

Answer 1

Answer: (B)

The magnetic field at any point inside the pipe is zero

Answer 2

Applying Ampere’s law to any closed path inside the pipe we find no current is enclosed. Hence $B = 0$