1. I'm having a final this week and I wanted to review some of the physics concepts, but I don't understand what the book is saying so I'm wondering if anyone can give me a site that is easy and understandable for me. (or you can write it down here) I mostly need to know the concepts on light refraction, mirrors, lens, and circuits because I don't understand them the most. (but if you can also write down the concepts for other topics it would be much appreciated. :] Thank YOU in advance!!