Near an infinitely large flat plate with a surface charge density o on each side, the field strength is** `E=delta/(in n^delta),` while the field produced by a point charge at a distance r frorn the chargo is Prove that for a uniformly charged disk with a surface charge density a (on each side), the electric field strength on the axis of the disk is the same as for an infinitely large flat plate if the distances arc small in comparison with the disk's radius R, and is the same as for a point charge if the distances are large ** Usually the value of the field strength given in textbooks is half the one given here, since there it is assumed that the charge is on a geometric plane