Question

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

• A. the magnetic field at all point 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)

Using Ampere’s circuital law over a circular loop of any radius less than the radius of the pipe, we can see that net current inside the loop is zero. Hence, magnetic field at every point inside the loop will be zero.