Question

Why internal surface of sphere, there is E = 0.
I mean why we can charge Van de Graaff from inside?

Answer 1

Because internal surface of sphere, there are many positive charge on the surface of the sphere like van de craaff. so,there are many electron field from everywhere. and inside, the electron fields are equal each other. beause the direction is opposited, so the net electron field is 0

Answer 2

in the centre of sphere it's make sense, but how to explan spot on the sphere.
may be I should ask the distributing of charge on the shell.