Question

.(3 pts) Suppose you shine an orange sodium laser (A =600 nm a in vacuum) nearly perpendicularly into a pool of water (nh20= 1.30) that is covered with a thin film of oil (noi=1.25). You notice that the oil film acts like an anti-reflective coating at the wavelength of your laser, meaning that the reflections are completely destructively interfering Given this observation, what can you conclude as the minimum thickness of the oil film? (Hint: Start by carefully drawing out a diagram of what is occurring.

Answer 1

distrutive interference incident light ray 1 гау2 air oil water phase change point ray 1 and ray 2 are 180 degree out of phase

the condition for distructive interference of light reflecting from the oil coating on water surface while, 11 al <nwater 21 aj tcos0=( m a m=1,2,3 consider m=1 and normal incidencecose=1 t=thickness of oil film n =refractive index of oilfilm=1.25 a = wavelegth of thereflected colour =600 nm minimum thickness of the coating for m=1 = 120nm