Answer Happy

A research paper published in the journal Applied Physics Letters describes experiments performed with three identical spherical conductors suspended from above by insulating wires the centers of all the spheres lie in the same horizontal plane. It was reported that a large voltage V applied to one sphere induced equal and opposite rotation in the two isolated spheres. The authors suggested that the isolated spheres were set into motion by electrostatic torque. Show, to the contrary, that this torque is zero.