I agree that you should aim for something historical. Since you're at AP level, it might be best to go back to the 1900's, since anything more recent than 1920 will be unfortunately too advanced for you to get a deep understanding of the problem. If I can recommend some literature, what about taking a look at the scientific chapters of Abraham Pais's biography of Albert Einstein - "Subtle is the Lord":http://www.amazon.com/Subtle-Is-Lord-Sc ... 241&sr=8-1
Pais excellently discusses both the scientific as well as the non-scientific aspects of Einstein's life. Thus he gives a really interesting discussion of the birth of e.g. special relativity and the scientific establishment at the time. You'll have essentially to read chapter III, which is probably some 50 pages (or less, if you cut the biographical part).