physics
posted by Sandhya .
Calculate the magnetic field at the center of a wire square that consists of 120 loops and has sides of length 5 cm and carries a current of 0.7 A.

For an exact solution, apply the BiotSavart law, which is explained at
http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law
and many other places. You can save time by applying it for the field due to a wire length on one side of the square, and multiplying by 4 x 120. Each of the four sides wil contribute equally to the B field in the middle of the loop.