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JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    A convex lens of focal length 12 cm is made of glass of \[\mu =\frac{3}{2}\]. What will be its focal length when immersed in liquid of \[\mu =\frac{5}{4}\]                     [MP PMT 1995, 2003]

    A)            6 cm                                         

    B)            12 cm

    C)            24 cm                                      

    D)            30 cm

    Correct Answer: A

    Solution :

                       \[\frac{{{f}_{l}}}{{{f}_{a}}}=\frac{{{(}_{a}}{{\mu }_{g}}-1)}{{{(}_{l}}{{\mu }_{g}}-1)}=\] \[\frac{\left( \frac{3}{2}-1 \right)}{\left( \frac{3/2}{5/4}-1 \right)}=\frac{5}{2}\]            \[\therefore \] \[{{f}_{l}}={{f}_{a}}\left( \frac{5}{2} \right)=\frac{12\times 5}{2}=30\]\[cm\]


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