question_answer

Blue light of wavelength 480 nm is most strongly reflected off a thin film of oil on a glass slab when viewed near normal incidence. Assuming that the index of refraction of the oil is 1.2 and that of the glass is 1.6, what is the minimum thickness of the oil film (other than zero)?

A) 100 nm

B) 200 nm

C) 300 nm

D) None of these

Correct Answer: B

Solution :

[b] \[2\mu t=n\lambda \Rightarrow t=\frac{n\lambda }{2\mu }\] \[\Rightarrow t=\frac{\lambda }{2\mu }=200nm\]