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 outside the cylinder at a distance x form the axis is

• A. $\frac{{\mu }_{0}I}{2\mu r}$
• B. $\frac{{\mu }_{0}I}{2\pi (x-r)}$
• C. $\frac{{\mu }_{0}I}{2\pi r^2}$
• D. $\frac{{\mu }_{0}I}{2\mu (x-r{)}^2}$

Answer 1

The correct option is A

$\frac{{\mu }_{0}I}{2\mu r}$

According to Ampere's Circuital Law $\oint \overrightarrow{B}.\overrightarrow{dl}={\mu }_{0}I\Rightarrow B\left(2\pi x\right)={\mu }_{0}I\Rightarrow B=\frac{{\mu }_{0}I}{2\pi x}$