An astronomical telescope has an angular magnification of magnitu… - Vidyadip

MCQ

An astronomical telescope has an angular magnification of magnitude $5$ for distant objects. The separation between the objective and the eye piece is $36 cm $ and the final image is formed at infinity. The focal length $f_o$ of the objective and the focal length $f_e$ of the eye piece are

A
$f_o = 45\, cm$ and $f_e = -9\, cm$
B
$f_o = 7.2\, cm$ and $f_e = 5\, cm$
C
$f_o = 50\, cm$ and $f_e = 10\, cm$
✓
$f_o= 30 \,cm$ and $f_e = 6\, cm$

✓

Answer

Correct option: D.

$f_o= 30 \,cm$ and $f_e = 6\, cm$

d
(d)In this case $|m|\; = \frac{{{f_o}}}{{{f_e}}} = 5$.... $(i)$

and length of telescope $ = {f_o} + {f_e} = 36$.... $(ii)$

Solving $(i)$ and $(ii),$

we get $f_e$ = 6 cm,${f_o} = 30\,cm.$

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