2. Questions Bank
  3. JEE Main & Advanced
  4. Physics
  5. Ray Optics

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

  • question_answer
    The focal length of the field lens (which is an achromatic combination of two lenses) of telescope is 90 cm. The dispersive powers of the two lenses in the combination are 0.024 and 0.036. The focal lengths of two lenses are [CPMT 2005]

    A)            30 cm and 60 cm                 

    B)            30 cm and ? 45 cm                                                                

    C)            45 cm and 90 cm                 

    D)            15 cm and 45 cm

    Correct Answer: B

    Solution :

                       For achromatic combination \[\frac{{{f}_{1}}}{{{f}_{2}}}=-\frac{{{\omega }_{2}}}{{{\omega }_{1}}}=-\frac{0.036}{0.024}=-\frac{3}{2}\]                    and \[\frac{1}{{{f}_{1}}}-\frac{1}{{{f}_{2}}}=\frac{1}{90}\]            solving above equations be get \[{{f}_{1}}=30cm,\ {{f}_{2}}=-45cm\]


You need to login to perform this action.
You will be redirected in 3 sec spinner