Two identical circular loops of radius 5cm are placed coaxially. One loop has 30 turns, the other 20 turns. Each carries a current of 4A, but in opposite directions. What is the magnitude and direction of the net magnetic field at their common centre?
a) 2.5×103μT, along the field of the 30-turn loop
b) 1.0×103μT, along the field of the 30-turn loop
c) 5.0×102μT, along the field of the 30-turn loop
d) 5.0×102μT, opposite to the field of the 30-turn loop