Question

An astronomical telescope has on objective and an eyepiece of focal lengths $10cm$ and $1cm$ respectively. Find its tube length in normal adjustment.

• A. $11cm$
• B. $10cm$
• C. $9cm$
• D. $1cm$

Answer 1

The correct option is A $11cm$

$f_0=10cm;f_e=1cm$

In normal adjustment,
Magnifying power $=\frac{f_0}{f_e}=\frac{10}{1}=10$
Tube length $=f_0+f_e$
$=(10+1)$
$=11cm$