Question

If a long hollow copper pipe carries a direct current, the magnetic field associated with the current will be :

• A. only inside the pipe
• B. only outside the pipe
• C. both inside and outside the pipe
• D. neither inside not outside the pipe

Answer 1

The correct option is B only outside the pipe

For a loop inside the hollow portion of the conductor, the current enclosed is zero until the loop is on the surface or inside the material of the conductor.
∴Binside=0∴Binside=0
For any loop outside, current enclosed by the amperian loop is not zero, hence magnetic field is non-zero.