A glass plate (n = 1.63) is covered with a thin, uniform layer of oil (n = 1.24)
ID: 1587179 • Letter: A
Question
A glass plate (n = 1.63) is covered with a thin, uniform layer of oil (n = 1.24). A light beam of variable wavelength from air is incident normally on the oil surface. Observation of the reflected beam shows destructive interference at 498.0 nm and constructive interference at 560.2 nm. From this information, calculate the thickness of the oil film.
I'm having a hard time grasping this whole concept of constructive and destructive reflection, so looking for a very thorough explanation of this problem! Thanks!
Explanation / Answer
There are no net phase difference for the two reflected rays.
Therefore for destructive interference
2t = lemda / n
2t = 498.0 / 1.63
2t = 305.52
t = 305.52/2
t= 152.76nm
Constructive interference
2t = lemda / n
2t = 560.0 / 1.24
2t = 451.61
t = 451.61/2
t= 225.80nm