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Geometrical Optics question

2018 · Q132
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Geometrical Optics question

2018 · Q132

NEETPhysicsGeometrical OpticsMCQ+4 / −1
An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
  1. A
    small focal length and large diameter
  2. B
    large focal length and small diameter
  3. C
    large focal length and large diameter
  4. D
    small focal length and small diameter
View written solutionFree

Correct answer: C

For telescope, angular magnification = f0fe{{{f_0}} \over {{f_e}}}fe​f0​​, which shows that focal length of objective lens to be large.

Angular resolution = D1.22λ{D \over {1.22\lambda }}1.22λD​ which is large, hence objective should have large focal length and larger diameter.

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