An electric current i is flowing through an infinitely  long conductor bent into a loop of the shape shown in fig. The magnitude and direction of magnetic field 

at the centre O of the circular part of the loop, will be

Let B₁and B₂ be the magnetic fields produced by circular and straight parts of the loop respectively. Then
${\mathrm{B}}_1=\frac{{\mathrm{\mu }}_0}{4\mathrm{\pi }}\cdot \frac{2\mathrm{\pi i}}{\mathrm{r}}$
(perpendicular to the plane of loop and in outward direction) 
${\mathrm{B}}_2=\frac{{\mathrm{\mu }}_0}{4\mathrm{\pi }}\cdot \frac{2\mathrm{i}}{\mathrm{r}}$
(perpendicular to the plane of the loop and in outward direction)
$\therefore \mathrm{B}={\mathrm{B}}_1+{\mathrm{B}}_2=\frac{{\mathrm{\mu }}_0}{4\mathrm{\pi }}\frac{2\mathrm{i}}{\mathrm{r}}(\mathrm{\pi }+1)$ in outward direction