1. The problem statement, all variables and given/known data A square loop of wire C, with side length 2a lies in a plane P and carries a steady electic current I. By using the Biot-Savart law show that the magnetic field B(r) at any point r in P but not in C is perpendicular to the plane P. Calculate the magnetic field at the centre of the wire. 3. The attempt at a solution Dotting with a would seem the normal way to do the first bit but I don't think this works so I think it must be to do with the vector product always being 0. I don't recall ever being taught how to calculate a line integral with a vector product inside it so really not sure where to begin. I expect there is a way to use symmetry to simpliify it. If my guess is correct then the component of one side of the square (x=a) is going to be (assuming centre is origin): (u*I/4pi)*(0,0, Integral -a and a of (a/((a^2+(y')^2)^3/2)dy') I think all 4 sides can be summed to make it 4 times that. I don't really have any idea what I'm doing though so if someone could explain it would be appreciated.