An infinitely long straight wire carrying current I is bent in a planer shape as shown in the diagram. The radius of the circular part is r. The magnetic field at the centre O of the circular loop is :

A

$$\large -\frac{\mu_0}{2\pi} \frac{I}{r}\left(\pi-1\right) \widehat{i}$$

B

$$\large \frac{\mu_0}{2\pi} \frac{I}{r}\left(\pi+1\right) \widehat{i}$$

C

$$\large \frac{\mu_0}{2\pi} \frac{I}{r}\left(\pi-1\right) \widehat{i}$$

D

$$\large -\frac{\mu_0}{2\pi} \frac{I}{r}\left(\pi+1\right) \widehat{i}$$