NEET Physics Ray Optics NEET PYQ-Ray Optics

An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of [NEET - 2018]

A) Large focal length and large diameter

B) Large focal length and small diameter

C) Small focal length and large diameter

D) Small focal length and small diameter

Correct Answer: A

Solution :

[a] For telescope, angular magnification\[\text{=}\frac{{{\text{f}}_{\text{0}}}}{{{\text{f}}_{\text{E}}}}\]

So, focal length of objective lens should be large.

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

So, objective should have large focal length \[({{f}_{0}})\] and large diameter D.