Question

The eyepiece of a refracting telescope has $f=9\text{cm}$. In the normal setting, seperation between objective and eyepiece is $1.8\text{m}$. Find the magnification.

• A. $20$
• B. $19$
• C. $18$
• D. $21$

Answer 1

The correct option is B $19$

Given $f_e=9\text{cm}=0.09\text{m}$
$l=1.8\text{m}=f_0+f_e$
$f_0=1.8-0.09=1.71\text{m}$
Magnification
$M=\frac{f_0}{f_e}=\frac{171}{9}=19$