### Magnetic Field

For each side
$B_z=\int_{-a/2}^{a/2} \frac{KI dx (a/2)}{(x^2+a^2/4)^{3/2}}=\frac{KI\sqrt{2}}{a} ^$
Total magnetic field is 4 times greater, that is, $B_z=4KI\sqrt{2}/a$.