Question

A current I flows along the length of an infinitely long, straight and thin-walled pipe. Choose the correct option?

• 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

The correct option is B The magnetic field at any point inside the pipe is zero

Applying Ampere's law $\oint B.dl={\mu }_{0}i$ to any closed path inside the pipe, we can understand that as the currect enclosed inside it is zero, the magnetic field will be equal to zero.