Question

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

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

Answer 1

The correct option is A 6 cm and 48 cm

$f_0+f_e=54$ and $\frac{f_0}{f_e}=m=8\Rightarrow f_0=8f_e$

$\Rightarrow 8f_e+f_e=54\Rightarrow f_e=\frac{54}{9}=6$

$\Rightarrow f_0=8f_e=8\times 6=48$