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  • The focal length of the objective and the eyepiece of a telescope are 50cm and 5cm respectively. If the telescope is focused for distinct vision on a scale distant 2m from its objective, then its m

The focal length of the objective and the eyepiece of a telescope are 50cm and 5cm respectively. If the telescope is focused for distinct vision on a scale distant 2m from its objective, then its magnifying power will be : 

Option: 1

-4


Option: 2

-8


Option: 3

+8


Option: 4

-2


Answers (1)

best_answer

Given : fo?=50 cm,  fe?=5 cm ,  uo?=−2m=−200 cm and  D=25 cm

Using the lens formula for the focal length of the objective lens,


\\ \frac{1}{v_{o}}-\frac{1}{u_{o}}=\frac{1}{f_{o}}$ \\ \\ $\therefore \frac{1}{v_{o}}-\frac{1}{-200}=\frac{1}{50} \\ \\ \Rightarrow v_{o}=\frac{200}{3} cm$ \\ \\Also, the magnification is given by, $m=\frac{v_{o}}{u_{o}}\left(1+\frac{D}{f_{e}}\right)$ \\ \\ $\therefore m=\frac{200 / 3}{-200}\left(1+\frac{25}{5}\right)$

We get the magnifying power comes out to be m=−2

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