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NEET Sample Paper NEET Sample Test Paper-10

  • question_answer
    A concave lens of focal length 10cm and a convex lens of focal length 20cm are placed certain distance apart. If parallel rays incident on the lens becomes converging after passing through other lens, then the separation between the lenses must be greater than.

    A)  zero                

    B)  \[5cm\]

    C)  \[10cm\]                     

    D)  \[9cm\]

    Correct Answer: A

    Solution :

    If rays are parallel to principal axis, then rays will converge if equivalent focal length is positive i.e.       \[\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}-\frac{d}{{{f}_{1}}{{f}_{2}}}>0\]                 \[\frac{1}{-10}+\frac{1}{20}-\frac{d}{(-10)\,(20)}>0\]


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