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RAJASTHAN PMT Rajasthan - PMT Solved Paper-1997

  • question_answer
    Two lenses in contact form an achromatic lens, their focal lengths are in the ratio 2:3 Their dispersive powers must be in the ratio of:

    A)  1 : 3                      

    B)         2 : 3                      

    C)  3 : 2                      

    D)         3 : 1

    Correct Answer: B

    Solution :

    Condition for achromatic lens couple is \[\frac{{{f}_{1}}}{{{f}_{2}}}=-\frac{{{\omega }_{1}}}{{{\omega }_{2}}}\] \[\frac{{{\omega }_{1}}}{{{\omega }_{2}}}=-\frac{2}{3}\] \[\therefore \] ratio of dispersive powers is \[~-2:3\]


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