Question

An astronomical telescope of ten fold angular magnification has a length of $44cm$. The focal length of the objective is :

• A. $44cm$
• B. $440cm$
• C. $40cm$
• D. $4cm$

Answer 1

The correct option is C $40cm$

In case of telescope, in normal adjustment,

$m=\frac{f_0}{f_e}=10$

and $f_0+f_e$= length of tube = 44 cm

$f_0=10f_e$ $10f_e+f_e=44\Rightarrow f_e=4$

$f_0=10\times 4=40cm$