A charge Q is uniformly distributed over a large plastic (non conducting) sheet.the field at a point close to a center of the plate near the surface is 20v/m .If the plate is replaced by a copper plate of the same geometrical dimensions and carrying the same charge Q then what is the electric field at that point

5 V m-1 is the correct answer as the charge Q is uniformly distributed over a large plastic sheet. 
Then electric field at a point close to the centre of the plate near the surface is 20 V/M. 
Plate is replaced by a copper plate of the same geometrical dimensions and carrying the same charge Q so that the electric field at that point is 5 V m-1.