Ray Optics and Optical Instruments - Result Question 64
67. An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of [2018]
(a) small focal length and large diameter
(b) large focal length and small diameter
(c) small focal length and small diameter
(d) large focal length and large diameter
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Answer:
Correct Answer: 67. (d)
Solution:
- (d) For telescope, angular magnification $=\frac{f_0}{f_E}$
So, focal length of objective lens should be large.
Angular resolution $=\frac{D}{1.22 \lambda}$ So, $D$ should be large.
So, objective lens of refracting telescope should have large focal length $(f_0)$ and large diameter $D$ for larger angular magnification.
