A long wire is bent into shape ABCDE as shown in fig. with BCD being a semicircle with centre O and

 

radius r metre. A current of I amp flows through it in the direction A → B →C → D→ E. Then the magnetic induction at the point O of the figure in vacuum is

• A

  ${\mathrm{\mu }}_0\left[\frac{\mathrm{i}}{2\mathrm{\pi r}}+\frac{\mathrm{i}}{4\mathrm{r}}\right]$

• B

  ${\mathrm{\mu }}_0\left[\frac{\mathrm{i}}{2\mathrm{\pi r}}-\frac{\mathrm{i}}{4\mathrm{r}}\right]$

• C

  ${\mathrm{\mu }}_0\mathrm{i}/4\mathrm{r}$

• D

  ${\mathrm{\mu }}_0\mathrm{i}/\mathrm{\pi r}$