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  • (a) Draw the ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for the resolving power of the telescope. (b) An astronomical telescope has an objective lens of focal length <img alt="20\

(a) Draw the ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for the resolving power of the telescope.

(b) An astronomical telescope has an objective lens of focal length 20\; m and eyepiece of focal length 1\; cm.

(i) Find the angular magnification of the telescope.

(ii) If this telescope is used to view the Moon, find the diameter of the image formed by the objective lens. Given the diameter of the Moon is 3.5\times 10^{6}m and radius of lunar orbit is 3.8\times 10^{8}m.

 

 

 

 
 
 
 
 

Answers (1)

a)

Resolving power 

=\frac{D}{1.22\lambda}

b)

i)

\text{Angular magnification}=\frac{f_o}{f_e}=\frac{20}{0.01}=2000

ii)

\\\frac{D}{d}=\frac{x}{f_o}\\d=\frac{Df_o}{x}=\frac{3.5\times10^6\times20}{3.8\times10^8}=0.184m

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Safeer PP

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