To concentric circular coils of 10 turns each are situated in the same plane. Their radii are 20 cm and 40cm and they carry currents of 0.2 and 0.3 A respectively in opposite directions. If `mu_0` is the permeability of vacuum then the magnetic field in Wbm-2 at the common centre is.

Options

A. `(35 mu_0)/4`
B. `(5 mu_0)/4`
C. `mu_0/80`
D. `(7mu_0)/80`

Answer

B