An astronomical refractive telescope has an objective of focal length 20 m and an eyepiece of focal length 2 cm.

Options

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.

Answer

A, B, C

Explanation

Tube length of telescope,
`f_0 + f_e = 20 + (0.02) = 20.02 m`
Hence option (A) is correct.
Magnification obtained by telescope,
`m=(f_0)/(f_e)=(20)/(0.02)=1000`
Hence option (B) is also correct.
In case of telescope, final image is inverted w.r object. Hence option (C) is also correct.