Question

The magnifying power of an astronomical telescope is $8$ and the distance between the two lenses is $54cm$. The focal length of eye lens and objective lens will be respectively :

• A. $6cm$ and $48cm$
• B. $48cm$ and $6cm$
• C. $8cm$ and $64cm$
• D. $64cm$ and $8cm$

Answer 1

The correct option is A $6cm$ and $48cm$

According to the question,

$f_o+f_e=54$ and $\frac{f_o}{f_e}=m=8\Rightarrow f_o=8f_e$
$8f_e+f_e=54\Rightarrow f_e=\frac{54}{9}=6$
$\Rightarrow f_o=8f_e=8\times 6=48$