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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
    What is the minimum thickness of a thin film required for constructive interference in the reflected light from it? Given, the refractive index of the film = 1.5, wavelength of the light incident on the film = 600 nm.

    A) 100 nm                                

    B) 300 nm

    C) 50 nm                                   

    D) 200 nm

    Correct Answer: A

    Solution :

    Condition for constructive interference is                 \[2\mu t=[2n+1]\frac{\lambda }{2}\] where, \[n=0,1,\text{ }2,3...\] For minimum thickness, \[n=0\]                                 \[2\mu t=\frac{\lambda }{2}\] \[\Rightarrow \]               \[t=\frac{\lambda }{4\mu }=\frac{6600\times {{10}^{-9}}}{4\times 1.5}\]                 = 100 nm


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