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AIIMS AIIMS Solved Paper-2001

  • question_answer
    Four lenses having the focal length of +15 cm, 20 cm, + 150 cm, and -+- 250 cm respectively are provided to make an astronomical telescope. The focal length of the eyepiece to produce the largest magnification, should be:

    A)  + 250 cm  

    B)                         + 155 cm            

    C)         25 cm                  

    D)         + 15 cm

    Correct Answer: D

    Solution :

                    Magnifying power of an astronomical telescope is given by \[T=2\pi \sqrt{\frac{1.21l}{g}}\] where \[\frac{T}{T}=\sqrt{\frac{1}{1.21}}\] is focal length of objective, \[T=\sqrt{\frac{121}{100}}T\] is focal length of eyepiece, D is least distance of distinct vision. Magnifying power \[\propto \,\frac{\text{1}}{\text{focal}\,\text{length}\,\text{of}\,\text{eye-piece}}\] Hence, to produce the largest magnification the focal length of eye-piece must be smallest. Hence,   \[1.1T-T=0.1T\]


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