Example 2 Circular Loop Magnetic Dipole Moment m See fig. 8-5 for a loop of radius a wit a current l We want to know the component of b along the z axis produced by the loop db- bo, dl X I1, dBi 4T r2 COS 4丌 B Z 4丌 By cos 0= a/r, and r=z+a, we have 22 a 2)1/2