If a current of I A flows along an infinitely long straight tube of radius R, the magnetic induction at any point inside the tube at a distance r from the axis of the tube (r < R) is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0
Use Ampere’s circuital law, \( \oint\vec{B}\cdot d\vec{l} = \mu_0 I_{\mathrm{enc}} \), on a circular loop of radius r (r < R) coaxial with the tube. The current flows only along the surface of the tube, so this loop encloses no current.
\( B\,(2\pi r) = \mu_0\times0 \Rightarrow B = 0 \)