Q. A current $i$ A flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is
A) Infinite
B) Zero
C) $\frac{\mu_{0}}{4\pi}\ .\frac{2i}{r}\ T$
D) $\frac{2i}{r}T$
Explanation
(b) Let $R$ be the radius of a long thin cylindrical shell.
To calculate the magnetic induction at a distance $r(r < R)$ from the axis of cylinder, a circular shell of radius $r$ is shown in figure.
Since, no current is enclosed in the circle so, from Ampere’s circuital law, magnetic induction is zero at every point of circle. Hence, the magnetic induction at any point inside the infinitely long straight thin walled tube (cylindrical) is zero.
[image:4_image131.emf]
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.