Question

Focal length of the objective lens and the eyepiece of an astronomical telescope are $100\text{cm}$ and $2\text{cm}$ respectively. Find the angular magnification produced in the case of the least strain on the eye.

• A. $70$
• B. $50$
• C. $60$
• D. $80$

Answer 1

The correct option is B $50$

Given:
$f_o=100\text{cm}$
$f_e=2\text{cm}$

In the case of the least strain on the eye $i.e.$ for normal adjustment, final image is formed at infinity.

So, angular magnification,

$m=\frac{f_o}{f_e}=\frac{100}{2}=50$

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