Two coaxial circular coils A and B, each of radius 10cm, are placed close to each other so that they share the same centre. Coil A has 50 turns and carries a current of 4A clockwise as seen from one side. Coil B has 100 turns and carries a current of 2A in the same clockwise sense. How does the magnetic field at the common centre produced jointly by the two coils compare with the field produced by coil A alone?
a) It becomes 1.5 times as large
b) It becomes half as large
c) It becomes twice as large
d) It becomes 3 times as large