Question

A current of $I$ ampere flows along an infinitely long straight thin walled hollow metallic cylinder of radius $r.$ The magnetic field at any point inside the cylinder at a distance $x$ from the axis of the cylinder is

• A. $\infty$
• B. $\frac{{\mu }_{0}I}{2\pi r}$
• C. $\frac{{\mu }_{0}I}{2\pi x}$
• D. $\text{zero}$

Answer 1

Answer: (D)

$\text{zero}$

Since no current is enclosed inside the hollow conductor, $i_{enclosed}=0$
Using Ampere's law, $\oint \overrightarrow{B}\cdot \overrightarrow{dl}={\mu }_0{i}_{enclosed}=0$
$\Rightarrow B\left(2\pi r\right)=0$
$\Rightarrow B=0$