A gaint refracting telescope at an observatory has an objective lens of focal length 15m. If an eye piece of focal length 1.0 cm is used, what is the angular magnification of the telescope ?

Explanation

`f_(0)=15m, f_(c)=10^(-2)m`
(a) Angular magnification of the telescope `=(f_(0))/(f_(e))=-(15)/(10^(-2))=-1500`
(b) Let `d` be the diameter of the image Angle subtended by image `=(d)/(f_(0))=(d)/(15)`
Angle subtended by diameter of moon `=(3.48xx16^(6)M)/(3.8xx10^(8)M)`
Equating `(d)/(15)=(3.48xx10^(6)M)/(3.8xx10^(8)M)`
On simplification , `d=13.73 cm`