Hi, So I still not sure how to apply like rhr rule in this setup in problem like the one in the following so I tried to do rhr in order to get the direction but it didn't work out. this is an example from halliday and resnick book. Figure 32-24 shows a wire segment,placed in a uniform magnetic field B that points out of the plane of the figure. If the segment carries a current i, what resultant magnetic force acts on it ? here is image of the problem at hand. Solution: f1 = f3 = -iLB so its equal to iL = <iL,0,0> B = <0,0,B> iLx B = <0,-iLB,0> so it points in the negative y direction I tried to do same thing now for circular part to get the directions. iL = i<rcostheta,rsintheta,0> B = <0,0,B> iL x B = <rsinthetaB,rcostheta,0> so since its a circle costheta will gets canceled by symmetry so it will be so it will have only a horizontal component equal to rsinthetaB ofcourse this works out in the problem when you do the integeral but its not right reasoning as the book have and book used rhr.