Question 160: Ray Optics

Question

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 :

Accepted Answer

$$\because$$ $$m = {{{f_o}} \over {{f_e}}}$$
$$ \Rightarrow 2 = {{{f_o}} \over {{f_e}}}$$ ...... (i)
and, $$l = {f_o} + {f_e}$$
$$ \Rightarrow 30 = {f_o} + {f_e}$$ ..... (ii)
$$ \Rightarrow 30 = {f_o} + {{{f_o}} \over 2}$$
$$ \Rightarrow 30 	imes {2 \over 3} = {f_o}$$
$$ \Rightarrow {f_o} = 20$$ cm

Answer

20 cm

Answer

30 cm

Answer

10 cm

Answer

15 cm

Ray Optics

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 :

Choose the correct answer: