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  • An astronomical refractive telescope has an objective of focal length 20m and an eyepiece of focal length 2cm. A. The length of the telescope tube is 20.02m.

An astronomical refractive telescope has an objective of focal length 20m and an eyepiece of focal length 2cm.
A. The length of the telescope tube is 20.02m.
B. The magnification is 1000.
C. The image formed is inverted.
D. An objective of a larger aperture will increase the brightness and reduce chromatic aberration of the image.

Answers (1)

The right answers to this question are options (a, b, and c)

Key concept :

  • Use to see heavenly bodies.
  • f_{objective}>f_{eye\; lens} and d_{objective}>d_{eye\; lens}
  • The intermediate image is real, inverted and small.
  • The final image is virtual, inverted and small.
  • Magnification:
  • m_{D}=-\frac{f_{0}}{f_{e}}\left ( 1+\frac{f_{e}}{D} \right ) and  m_{\infty }=-\frac{f_{0}}{f_{e}}
  • Length :
  • L_{D}=f_{0}+u_{e}=f_{0}+\frac{f_{e}D}{f_{e}+D} and  L_{\infty }=f_{0}+f_{e}

The length of the telescope tube is

f_{0}+f_{e}=20+(0.02)=20.02\; m

Also,

m=\frac{20}{0.02}=1000

Also, the image formed is inverted.

Posted by

infoexpert23

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