Two concentric coplanar circular loops of radii r1 and r2 carry currents i1 and i2, respectively, in opposite directions (one clockwise and the other anticlockwise.) The magnetic induction at the centre of the loops is half of that due to i1 alone at the centre. If r2 = 2r1 , the value of i2/i1 is
Magnetic field at the centre due to smaller loop
….(i)
Due to bigger loop,
So, net magnetic field at centre
According to question,