A square conducting loop of length ‘L’ carries a current ‘i’. the magnetic field at the center of the loop is

Magnetic field at the center due to either arm B1=μ04π×iL/2sin450+sin450 =μ04π×22iLField at center due to the four arms of the square B=4B1=4×μ04π×22iL⇒B ∝ 1L .