Magnetic induction at a distance ‘r’ from the axis of a very long current carrying straight wire is ${\mathrm{B}}_1$. Now the wire is bent to form a circular loop of radius ‘r’ as shown in figure. The magnetic induction at the centre of the circular loop is found to be ${\mathrm{B}}_2$. Then  $\frac{{\mathrm{B}}_1}{{\mathrm{B}}_2}$ is equal to

• A

  $\frac{\mathrm{\pi }-1}{\mathrm{\pi }}$

• B

  $\frac{3\left(\mathrm{\pi }-1\right)}{\mathrm{\pi }}$

• C

  $\frac{2\mathrm{\pi }}{\mathrm{\pi }-1}$

• D

  $\frac{1}{\mathrm{\pi }-1}$