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

`1500 ' 13.5 cm`

Explanation

Here, `f_0 = 15 m, f_e = 1 cm = (1)/(100) m`
Angular magnification `= (f_0)/(f_e) = (15)/(1//100) = 1500`
Diameter of image of moon formed by objective lens
=`prop. F_0 = (3.42 xx 10^6)/(3.8 xx 10^8) xx 15 m = 0.135 m`
=`13.5 cm`.