A) 1000 nm
B) 500 nm
C) 750 nm
D) 250 nm
Correct Answer: D
Solution :
Let t is thickness of the air film and \[\mu \] be the refractive index. The condition for darkness of the film is \[2\mu t\cos \gamma =n\lambda .\] For minimum thickness \[t,\,n=1\] and for normal incidence \[\gamma =0,\,\mu =1\] for air. Therefore, \[2t=\lambda \]or \[t=\frac{\lambda }{2}=\frac{500}{2}=250\,nm\]You need to login to perform this action.
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