I've got all the basics like what exactly is a standing wave, transverse and etc etc as well as all the lingo. But I just don't get what they want when they're talking about In phase or out of phase. I pretty much don't understand phase difference at all. Also could someone help in explaining diffraction gratings. I'm fed up with my teacher spending 40 minutes of the class talking about how great he is and how he's managed to somehow add 1412 people on facebook over the weekend. Whilst leaving us 20 minutes of real lesson. HELP please. I'm desperate!
