Khan Academy and YouTube is my life support for things like these, just put in some effort and you should be good to go. For me the approach I like to take sometimes is not listen during class, then go to buy 200 mg caffeine tablets on a Wednesday night, consume like 20 of them, and then watch 12 hour course videos to catch up. It works when I'm in...... reply
Before learning quantum, you will have to have basic knowledge in Classical mechanics. Because quantum is a deviation from classical. The theory part of quantum is sooo much fun but also at the same time, if not understood correctly, you will be left with confusions that will hinder with your future learning of quantum. Then there comes mathematica...... reply
Assuming you’re genuinely asking and may also be a beginner, I highly recommend reading this textbook:
http://www.boydnlo.ca/wp-content/uploads/2020/10/Optics-in-Our-Time.pdf
(Free by the way- if the link doesn’t work just search up Optics in our Time) It really helped me get through it !! (If it’s not enough, I also recommend QED by Richar...... reply