PPT Slide
Both rays reflected from media in which wave moves more slowly
phase difference only due to path difference
if ? = 2?m, then constructive interference
if ? = ? (2m-1), then destructive interference
? = (2?nwater/?)(2t) = ? (2m-1), i.e. t = (2m-1)(?/4nwater)
non-reflecting glass uses this principle