I learn in high school Physics class that when light travels from a medium to a more optically dense thin film, then the reflected rays will destructively interfere with each other. My questions are:
Will the interference of the rays being reflected of the top surface with the rays being reflected of the bottom of the film ever be constructive? Can you explain why it will be constructive?
Then in what situations will the rays destructively interfere with each other?
And if the reflected ray (the one reflected off the bottom of the thin film) can be made so that it constructively interferes, how can it then be said that the bottom wave is always 180 degrees out of phase? Because to constructively interfere, you cannot be 180 degrees out of phase? So how can it be said that all reflected rays of the bottom of an more optically dense material will be 180 degrees out of phase with the reflected ray on top?
Thank you so much! This would immensely help my understanding of the topic! Please, though, try to answer the question at the level of a high school student.