A square conducting loop of side length L carries a current I. The magnetic field at the centre of the loop is

Magnetic field at the centre due to either armB=   μ04π ×  IL/2  sin 450  +  sin 450=μ04π ×  22ILField at centre due to the four arms of the squareB=4B1 =4×μ04π ×  22ILi.e.,  B  ∝  1L