Question

If a long hollow copper pipe carries a current, then produced magnetic field will be

• 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 1

Answer: (B)

Use Ampère's law
$\oint B . d l=\mu_{0} i_{\text {enclosed }}$.
$\text { Outside }: i_{\text {enclosed }} \neq 0$ (some value)
$\Rightarrow B \neq 0 $
$\text { Inside }=i_{\text {enclosed }}=0$
$ \Rightarrow B=0 .$