As stated in this article at page 5, capacitance of a capacitor is generally expressed with the following formula:
My question is about surface area
S, where it is described as "On aluminum electrolytic capacitor, “S” is effective surface area of anode foil enlarged to 60 to 150 times of the projected area through etching process.". What is the etching process here? And how to understand "anode foil enlarged to 60 to 150 times of the projected area"?
Second question about constant
8.855. Is it widely accepted constant value, or changing at some conditions?