A current I = 3 A flows through a wire perpendicular to the paper and towards the reader at A and back in the opposite direction at C. Consider the wires below the plane at A and C to be semi-infinite. In the figure, L1 = 3 m, R = 6 m, and L2 = 6 m and there is a B = 2.37 T magnetic field into the paper (not including the field due to the current in the wire). Caution: It may be necessary to take into account the contribution from the long straight wire which runs up to and down from the underneath side of the page. Image: http://img28.imageshack.us/img28/5329/newpictureiv.png [Broken] What is the magnitude of the magnetic field at the center of the arc O due to the current in the wire (T)? This is what I've done so far: For the arc portion of the circle, I used B = Mu(0)xI/8R For each of the straight portion, I used the equation for a long straight wire, which is: B = Mu(0) x I/(2 x pi x a). Since each portion of the wire is going in a different direction (i, j, k components), I took each field, squared it and added them all then took the square root. But this is not the right answer...Not sure where I'm going wrong?