As shown in the figure, a long straight conductor with semicircular arc of radius $\frac{\pi}{10} \mathrm{~m}$ is carrying current $\mathrm{I}=3 \mathrm{~A}$. The magnitude of the magnetic field, at the center O of the arc is: (The permeability of the vacuum $$ \left.=4 \pi \times 10^{-7} \mathrm{NA}^{-2}\right) $$