Question

The focal lengths of objective and eye lens of an astronomical telescope are $100cm$ and $5cm$, respectively. Calculate the magnifying power and length of an astronomical telescope for relaxed eye.

Answer 1

Focal length of objective$=f_o=100cm$,

Focal length of eye lens$=f_e=5cm$,

$\therefore$ Length of the astronomical telescope is given by,

$L=f_o+f_e=100cm+5cm=105cm$

Magnifying power of astronomical telescope is given by,

$M=\frac{f_o}{f_e}=\frac{100}{5}=20$