I realize I actually don't understand the concept of a battery (potential difference) and a capacitor.
From what I know a battery is something that provides a "drive" for electrons. In other words, take a 90V battery for instance, that just means 90J/C, which means it takes 90J to drive one coulomb of charge across a device. So my question is, where does the word "potential difference" really come in? I know it from textbook memory that it just a, well, a potential difference between two points. But I don't understand what that has to do with a battery (other than units), to me it seems like a Battery is just Electrical Potential, not Potential difference.
Now what about a capacitor? My teacher said to think of a capacitor as a temporary battery, something that stores charges. My question is why do we even have something like that exists? If it is just a temporary battery, why don't we just put a permanent one there? I don't understand, so what if a capacitor hold charges. Why do we even need something that hold charges.