Question

(i) A giant refracting telescope has an objective lens of focal length $15m$. If an eye piece of focal length $1.0cm$ is used. What is the angular magnification of the telescope?
(ii) If this telescope is used to view the moon. What is the diameter of the image of the room formed by the objective lens? The diameter of the moon is $3.48\times {10}^{8}m$ and the radius of lunar orbit is $3.8\times {10}^{8}m$

Answer 1

(i)

Angular magnification of a refracting telescope is given by:

$m_o=\frac{f_o}{f_e}$

$m_o=\frac{1500}{1}=1500$

(ii)

Diameter of the image of the moon formed by objective is:

$d=\alpha f_o$

$d=\frac{\text{Diameter of the moon}}{\text{Radius of the lunar orbit}}{f}_o$

$d=\frac{3.48\times {10}^8}{3.8\times {10}^8}\times 15$

$d=13.736m$