In normal adjustment, for a refracting telescope, the distance be… - Vidyadip

MCQ

In normal adjustment, for a refracting telescope, the distance between objective and eye piece is $30\,cm$. The focal length of the objective, when the angular magnification of the telescope is $2$ , will be $.....cm$

✓
$20$
B
$30$
C
$10$
D
$15$

✓

Answer

Correct option: A.

$20$

a
$f _{0}+ f _{ e }=30$

$m =\frac{ f _{0}}{ f _{ e }}$

$2=\frac{ f _{0}}{ f _{ e }} \Rightarrow f _{0}=2 f _{ e }$

So $f _{0}+\frac{ f _{0}}{2}=30$

$f _{0}=20\,cm$

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