The order in which they arrange the chapters is really weird. They do wave-particle duality in Unit 1 yet the wave chapter (interference etc) is at the end of the book lol
I found waves really hard at the beginning of the year, we did unit 2 first then unit 1. Unit 1 in comparison is really easy as it's mostly memorisation. Physics was really hard then now I think it's my best subject (well, not exactly but lowest grade boundaries of all my subject lol) apart from the ISA which is pain in the neck