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Q. For a telescope, larger the diameter of the objective lens

Rajasthan PMTRajasthan PMT 2007Ray Optics and Optical Instruments

Solution:

The resolving power of a telescope is its ability to show two distant closely lying objects as just separate. The reciprocal of resolving power is the limit of resolution of the telescope.
Limit of resolution $ =1.22\frac{\lambda }{d}rad $
where $ \lambda $ is wavelength and $ d $ the aperture (diameter). Hence, to reduce the limit of resolution of a telescope, we must use objective lens of large aperture $ (d) $ . Larger the aperture of the objective lens, smaller the limit of resolution or greater the resolving power of the telescope.