A very long straight wire carries current I. In the middle of the wire a right-angle bend is made. The bend forms an arc of a circle of radius r as shown in the figure below. Figure: http://east.ilrn.com/graphing/bca/user/appletImage?dbid=1161207397 [Broken] Lets say the permeability of free space is mu. So I believe the answer is ((mu*I)/(4*pi*r))*(pi/2), which equals to (mu*I)/(8*r). It says the answer is wrong... Can anyone help?