Question

A gaint refrecting telescope at an observatory has an objective lens of focal length `15 m`. If an eye piece lens of focal length `1 cm` is used, find the angular magnification of the telescope.
If this telescope is used to view the moon, what is the diameter of image of moon formed by objective lens ? The diameter of the moon is `3.42 xx 10^6 m` and radius of lunar orbit is `3.8 xx 10^8 m`.

Answer 1

Correct Answer - `1500 ; 13.5 cm`
Here, `f_(0) = 15 cm, f_(e) = 1 cm = (1)/(100)m`
Angular magnification `= (f_(0))/(f_(e)) = (15)/(1//1100) = 1500`
Diameter of image of moon formed by objective lens
`= alpha f_(0) = (3.42 xx 10^(6))/(3.8 xx 10^(8)) xx 15 m = 0.135 m`
`= 13.5 cm`