Question

The objective of an astronomical telescope has a focal length of $100\text{cm}$. The telescope is focused for normal vision of distant objects when tube length is $1.1\text{m}$. Find magnifying power of the telescope.

Answer 1

Given,
Focal length of objective, $f_o=100\text{cm}$

Length of objective, $L=1.1\text{m}=110\text{cm}$

In case of normal adjustment, $L=fo+fe$

$\Rightarrow 110=100+fe$

$\therefore f_e=10\text{cm}$

Now, magnifying power,

$m=|\frac{-fo}{fe}|=\frac{100}{10}=10$