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9. Ray optics abd optical instruments — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics9. Ray optics abd optical instruments1 Mark
MCQ
An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
  • A
    small focal length and large diameter
  • B
    large focal length and small diameter
  • C
    small focal length and small diameter
  • ✓
    large focal length and large diameter
✓

Answer

Correct option: D.
large focal length and large diameter
d
For telescope, angular magnification $=\frac{f_{0}}{f_{e}}$

Angular resolution $=\frac{D}{1.22 \lambda}$ should be large.

So, objective lens should have large focal length $\left(f_{o}\right)$ and large diameter $D$ for large angular

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