1. The problem statement, all variables and given/known data We have contours C1 and C2 located in vacuum and there are constant currents in them, I1 and I2 respectively. Find the expression for magnetic force that acts on one very small element (dl) of the circle C2 and it's coming from one very small element of the contour C1. Sketch the contours with all the vectors that appear in the expression. 2. Relevant equations F=IlxB 3. The attempt at a solution This is how i tried to solve it. First, the formula for magnetic force is F=IlxB but, since i have to choose very small elements of the contours it means that i am only interested in dl and not the whole lenght of the contour l so force coming form the one small element of C1 and it's acting on one small element of C2 should be F=I2dl2xB where I2 is the current in C2, dl2 is the small element of C2 and B is magnetic induction vector of one element of C1 in the point where dl2 si located, which means that i should find B. Using Biot-Savart's law we have B=μ0I1dl1/(4πr2) where r is the distance from one element to another, now, since axb=absinα , α-angle between a and b then, the final solution is F=μ0I2I1dl1dl2/(4πr2) Now, i need to know if this is correct, then i'll do the sketch. So, i'd appreciate any help here.