Two circular coils of radii 5 cm and 10 cm carry currents of 2 A. The coils have 50 and 100 turns respectively and are placed in such a way that their planes as well as their centres coincide. Magnitude of magnetic field at the common centre of coils is
a. - 8π×10−4 T if currents in the coils are in same sense
b. - 4π×10−4 T if currents in the coils are in opposite sense
c. - zero if currents in the coils are in opposite sense
d. - 8π×10−4 T if currents in the coils are in opposite sense