Question

An astronomical refracting telescope will have large angular magnification and high angular resolution when it has an objective lens of

Answer 1

Hi.

An astronomical refracting telescope will have large angular Magnification and high angular resolution, when it has the objective lens of large focal length and large diameter.

Explanation ⇒ 

We know,
For Telescope,  Angular Magnification = $\frac{f_{0} }{f_e}$

From this relation, It is clear that if angular magnification is large then Focal length must be large.

Now, Angular Resolution = D/1.22λ 
where, λ = wavelength.
and D = Diameter

According to the Question, Angular Resolution is large, therefore diameter must be large, since they are directly proportional.

Hence, Astronomical refracting telescope must have the large Focal length and large Diameter.


Hope it helps.