Okay so I appreciate that as a capacitor is being charged it begins with zero charge stored on it, and slowly fills up. But I don't understand why the voltage varies.
The book says 'Each time we add a little extra charge (Q) this has to be done by increasing the voltage... [as] we are doing work against the repulsion between like charges'. I don't understand this because why is the battery now all of a sudden choosing how much energy it, gives each unit of charge? Surely the voltage should be constant, if units of charge have excess energy surely they can just use it up as heat like they do in normal battery light circuits? I don't understand why the battery is now selective about how much energy each unit of charge receives?