Figure shows a square loop ABCD with edge length a. The resistance of the wire ABC is r and that of ADC is 2r. The value of magnetic field at the centre of the loop assuming uniform wire is

According to question resistance of wire ADC is twice that of wire ABC. Hence current flows through ADC is half that of ABC i.e.  .Also    Magnetic field at centre O due to wire AB and BC  (part 1 and 2)   and magnetic field at centre O due to wires AD and DC (i.e. part 3 and 4)  Also, i1 = 2i2.  So (B1 = B2) > (B3 = B4)Hence net magnetic field at centre O