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NEET Sample Paper NEET Sample Test Paper-3

  • question_answer
    A bulb is placed at a depth of \[2\sqrt{7}\] in water and a floating opaque is placed over the bulb, so that the bulb is not visible from the surface. The radius of the disc should be at least: (\[\mu \] water\[=4/3\])

    A)  \[42\,m\]                     

    B)  \[6\,m\]

    C)  \[2\sqrt{7m}\,\]                      

    D)  \[12m\]

    Correct Answer: B

    Solution :

        If the bulb is not visible, it must be ray (light) coming from the bulb makes an angle equal or greater than critical angle, to the normal at the surface. So,    \[\sin \theta \,\,c=\frac{1}{\mu }=\frac{r}{\sqrt{{{r}^{2}}+28}}\]                 \[\mu =\frac{4}{3}\] \[\Rightarrow \]               \[r=6\,m\]


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