Magnetics

The magnetic field at the centre of a wire loop formed by two semicircular wires of radii \(R_1=2 \pi \mathrm{m}\) and \(R_2=4 \pi \mathrm{m}\), carrying current \(\mathrm{I}=4 \mathrm{~A}\) as per figure given below is \(\alpha \times 10^{-7} \mathrm{~T}\). The value of \(\alpha\) is ________. (Centre \(\mathrm{O}\) is common for all segments)