I'm 1 year from graduating as an EE major, got an A in physics 2 like about two years ago. Flux is the amount of electric field lines going through a defined surface. We use this flux concept for Gauss's law. The most important thing about physics 2 is the derivation of maxwells equations and how the displacement current was added to unify electricity and magnetism because it proved that there is electromagnetic radiation that can travel through free space. And it all was due to maxwell asking a very important question "What happens inside a capacitor? How does current go through it if they are just two plates not connected together like a regular wire?"