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10th Class Science Light - Reflection and Refraction Question Bank Light

  • question_answer
    Two media are separated by a plane surface. Speed of light in one medium is \[\text{2}.0\text{ }\times \text{ 1}{{0}^{\text{1}0}}\text{ cm}/\text{sec}\]and in the other the speed it is\[\text{2}.\text{4 }\times \text{ 1}{{0}^{\text{1}0}}\text{ cm}/\text{sec}\]. The critical angle for a ray going from the first medium into the second will be

    A)  \[{{\sin }^{-1}}\frac{1}{2}\]        

    B)         \[{{\sin }^{-1}}\left( \frac{5}{6} \right)\]  

    C)  \[{{\sin }^{-1}}\frac{5}{12}\]      

    D)         \[{{\sin }^{-1}}\left( \frac{1}{\sqrt{2}} \right)\]

    Correct Answer: B

    Solution :

     \[\sin C=\frac{{{\mu }_{1}}}{{{\mu }_{2}}}=\frac{Velocity\,\,of\,\,light\,\,in\,\,1st\,\,medium}{Velocity\,\,of\,light\,\,in\,\,2nd\,\,medium}\]where, \[C=\] critical angle \[\therefore \]  \[\sin C=\frac{2\cdot 0\times {{10}^{10}}}{2\cdot 4\times {{10}^{10}}}=\frac{20}{24}=\frac{5}{6}\] \[\Rightarrow \]                   \[C\mathbf{=si}{{\mathbf{n}}^{\mathbf{-1}}}\frac{\mathbf{5}}{\mathbf{6}}\]


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