Understanding the physics of "induced charge" over a perfect conductor When we put a perfect conductor, let's say a sphere inside an external electric field, there will be a surface charge distribution different from 0 even though the sphere is electrically neutral. I don't really understand: I have a sphere totally neutral, so with NO free charges. I put it inside an electric field and then suddenly some "free charges" will move up to the surface and distribute in function of the electric field. How can this be? I'd understand if I had initially a non neutral conducting sphere with a total net charge Q (evenly distributed over the sphere, in other words ##\sigma (\theta , \phi ) = \sigma _0 \neq 0##). But when there's no free charges, how can "free charges" go over the surface of the sphere? I'd understand if you'd call those charges "charges of polarization" but they are not. They are not "bound charges" (according to Griffith's terminology if I'm not wrong), they are "free charges". Can somebody explains me what's going on? Thank you.