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

Options

A. both inside and outside the pipe
B. outside the pipe only
C. inside the pipe only
D. neither inside nor outside the pipe.

Answer

B

Explanation

Using Ampere.s circuital law `oint B.dl =mu_(0) i_("enclosed")`.
Outside : `i_("enclosed") ne 0` (some value) `rArr B ne 0`
Inside : `i_("enclosed") =0 rArr B=0`