Derive an expression for the magnetic field strength at distance d from the center of a straight wire of finite length l that carries current i. express your answer in terms of the variables d, l, i, and appropriate constants. part b)determine the field strength at the center of a current-carrying square loop having sides of length 2r. express your answer in terms of the variables r, i, and appropriate constants. part c)compare your answer to part b to the field at the center of a circular loop of diameter 2r. do so by computing the ratio bsquarebcircle. express your answer to two significant figures and include the appropriate units.