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Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2005

  • question_answer
    The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5:3. If the focal length of the concave lens is 15 cm, then the nature and focal length the other lens would be

    A)  convex, 9 cm                    

    B)  convex, 9 cm

    C)  convex, 25 cm                 

    D)  convex, 25 cm

    Correct Answer: A

    Solution :

    The condition for achromatism is \[\frac{\omega }{\omega '}=-\frac{f}{f'}\] Given:     \[\frac{\omega }{\omega '}=\frac{5}{3},\]\[f=-15cm\] So,          \[\frac{5}{3}=\frac{-(-15)}{f'}\] or            \[f'=+9cm\](convex)


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