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JIPMER Jipmer Medical Solved Paper-2000

  • question_answer
    The minimum thickness of air film which appears dark when viewed under 500 nm light normally is:

    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 \[t=\frac{\lambda }{2}=\frac{500}{2}=250\,nm\]


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