Maxwell coil comprising 3 sub-coils. The smaller sub-coils have a radius of $\sqrt {4/7}$ of the radius of the big coil. The axial distance between each sub-coil is $\sqrt {3/7}$ of the radius of the big coil.
vfpt_maxwell_coil_geek3_wikimedia.png
You are permitted to use this image freely, for any legal purpose including commercial (the permission is given, so there is no need to ask for it explicitly again), but you must always include the following credits:
by Geek3, Wikimedia Commons, CC-BY-SA-4.0