An astronomical telescope consists of two converging lenses. One of them of large aperture and large focal length is called objective lens and the other one, of smaller focal length and smaller aperture is called the eyepiece. It is used to see distant objects which are not seen clearly with naked eyes. The image formed by the objective lens acts as an object for the eyepiece and the final image produced by the eyepiece is magnified.
Question: 1
The images formed by the objective lens and the eyepiece are respectively :
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In an astronomical telescope:
Objective \(\rightarrow\) Real image
Eyepiece \(\rightarrow\) Virtual image
The focal length of objective lens (\(f_o\)) is larger than the focal length of eyepiece (\(f_e\)).
Its magnifying power can be increased by increasing the focal length of objective lens (\(f_o\)).
The distance between two lenses is more than \((f_o+f_e)\).
The magnifying power can be decreased by increasing the focal length of eyepiece.
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The Correct Option isC
Solution and Explanation
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Question: 4
An astronomical telescope has objective lens and eyepiece of focal lengths \(80\,\text{cm}\) and \(4\,\text{cm}\) respectively. To view the image in normal adjustment, the lenses must be separated by a distance of :
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For normal adjustment:
\[
L=f_o+f_e
\]
Always add the focal lengths of objective and eyepiece.
Consider the telescope described in question (iv)(a). Its magnifying power in normal adjustment will be :
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For astronomical telescope in normal adjustment:
\[
M=\frac{f_o}{f_e}
\]
Large objective focal length and small eyepiece focal length produce high magnification.