Electrostatic clamps are used for holding workpieces while they are being machined, for holding silicon wafers during electron beam microfabrication, etc. They comprise an insulated conducting plate maintained at a potential of several thousand volts covered with a thin insulating sheet. The workpiece or the wafer rests on the sheet and is grounded. It is advisable to apply a film of oil to the sheet to prevent sparking.
One particular type operates at 3000 volts and has a holding power of 2 atmospheres (2 x 10^5 pascals). If the insulator is Mylar (relative permittivity = 3.2), what is its thickness?