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

  • question_answer
    The minimum deviation produced by a glass prism having an angle of \[60{}^\circ \] is \[30{}^\circ \]. If the velocity of light in vacuum is \[3\times 1010\text{ }cm/sec,\]then its velocity in glass will be

    A) \[~\text{2}.\text{12 }\times \text{ 1}{{0}^{\text{1}0}}\text{ cm}.{{\text{s}}^{-\text{1}}}\]            

    B)  \[\text{2}.\text{52 }\times \text{ 1}0\text{ cm}.{{\text{s}}^{-\text{1}}}\]  

    C) \[2.21\times {{10}^{10}}cm.{{s}^{-1}}\]

    D)         \[\text{2}.\text{82 }\times \text{ 1}{{0}^{\text{1}0}}\text{ cm}.{{\text{s}}^{-\text{1}}}\]

    Correct Answer: B

    Solution :

                    \[\mu =\frac{\sin \left( \frac{A+{{\delta }_{m}}}{2} \right)}{\sin A/2}\]                    \[=\frac{\sin \left\{ \left( \frac{60+30}{2} \right) \right\}}{\sin (60/2)}=\frac{\sin {{45}^{o}}}{\sin {{30}^{o}}}\]                    \[=\frac{1/\sqrt{2}}{1/2}=\sqrt{2}\]                    \[\mathbf{=1}\mathbf{.414}\] Velocity in glass\[=\frac{Velocity\,\,in\,\,vacuum}{\mu }\]                    \[=\frac{3\times {{10}^{10}}}{1.414}\]                    \[\mathbf{=2}\mathbf{.12\times 1}{{\mathbf{0}}^{\mathbf{10}}}\mathbf{cm/sec}\mathbf{.}\]


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