Question

The objective lens 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 the magnifying power of the telescope.

• A. $10$
• B. $11$
• C. $13$
• D. $12$

Answer 1

The correct option is A $10$

Given:
$f_o=100\text{cm}$
$L=1.1\text{m}=110\text{cm}$

When the telescope is focused for normal vision of distant objects, the tube length is given by,

$L=f_o+f_e$

$\Rightarrow 110=100+f_e$

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

Now, magnifying power,

$m=\frac{f_o}{f_e}=\frac{100}{10}=10$

Hence, option $\left(A\right)$ is the correct answer.