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. Neither inside nor outside the pipe
• D. Both inside and outside the pipe

Answer 1

Answer: (B)

Only outside the pipe

Answer 2

Because for inside the pipe $i = 0$

$\therefore B = \frac { \mu _ { 0 } i } { 2 \pi r } = 0$