A thin oil film with varying thickness is floating on water surface (n = 1.00). When the foil is lighted from above with white light it can be seen different colors in the reflected light (see picture).

1. What is the oil thickness t at point B when yellow color is seen?
2. Why no color is seen at point A but only a dark area?

Air Yellow Blue Red Yellow Oil Blue Dark no = 1.50 A B Water ny =1.33