KVPY Sample Paper KVPY Stream-SX Model Paper-5

  • question_answer
    In the figure ABC is the cross section of a right angled prism and BCDE is the cross section of a glass slab. The value of \[\theta \] so that light incident normally on the face AB does not cross the face BC is \[(given\,{{\sin }^{-1}}(3/5)=37{}^\circ )\]

    A) \[\theta \le 37{}^\circ \]             

    B) \[\theta <37{}^\circ \]

    C) \[\theta \le 53{}^\circ \] 

    D) \[\theta <53{}^\circ \]

    Correct Answer: C

    Solution :

    [B] \[A=90-\theta \] \[{{r}_{2}}=A=90-\theta >{{\theta }_{C}}\] \[\cos \theta >\sin {{\theta }_{C}}=\frac{6/5}{3/2}=\frac{4}{5}\] \[\Rightarrow \theta <{{\cos }^{-1}}\frac{4}{5}=37{}^\circ .\]  

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