In normal adujstment, for a refracting telescope, the distance between objective and eye piece is $30 \mathrm{~cm}$. The focal length of the objective, when the angular magnification of the telescope is 2 , will be :
Solution
<p>$\because$ $m = {{{f_o}} \over {{f_e}}}$</p>
<p>$\Rightarrow 2 = {{{f_o}} \over {{f_e}}}$ ...... (i)</p>
<p>and, $l = {f_o} + {f_e}$</p>
<p>$\Rightarrow 30 = {f_o} + {f_e}$ ..... (ii)</p>
<p>$\Rightarrow 30 = {f_o} + {{{f_o}} \over 2}$</p>
<p>$\Rightarrow 30 \times {2 \over 3} = {f_o}$</p>
<p>$\Rightarrow {f_o} = 20$ cm</p>
About this question
Subject: Physics · Chapter: Optics · Topic: Lenses and Optical Instruments
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