2. Solved Papers
  3. CMC Medical

CMC Medical CMC-Medical VELLORE Solved Paper-2009

  • question_answer
    A light of wavelength 5890\[\overset{\text{o}}{\mathop{\text{A}}}\,\]falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light is

    A)  \[2.945\times {{10}^{-7}}m\]    

    B)  \[3.945\times {{10}^{-7}}m\]

    C)  \[4.95\times {{10}^{-7}}m\]                       

    D)  \[1.945\times {{10}^{-7}}m\]

    Correct Answer: A

    Solution :

                    If thin film appears dark \[2\mu t\,\cos r\,=n\lambda \] For normal incidence\[r=0{}^\circ \] \[\Rightarrow \]               \[2\mu t=n\lambda \Rightarrow t=\frac{n\lambda }{2\mu }\] \[\Rightarrow \]               \[{{t}_{\min }}=\frac{\lambda }{2\mu }=\frac{5890\times {{10}^{-10}}}{2\times 1}\]                        \[=2.945\times {{10}^{-7}}\,m\]


You need to login to perform this action.
You will be redirected in 3 sec spinner