Ncert Exercises & Solutions

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

(a) The length of the telescope tube is 20.02 m.
(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.

1. (a), (b) and (c)

2. (b), (c) and (d)

3. all of the above

4. none of the above

(1, 2, 3) Hint: The length and magnification of the telescope depend on the focal lengths of the objective and the eyepiece of the telescope.

Step 1: Find the length of the telescope.

The length of the telescope tube = $f_{o} + f_{e} = 20 + (0.02) = 20.02 m$

Step 2: Find the magnification of the telescope.

Also, m= $\frac{20}{0.2}$ = 1000

Also, the image formed is inverted.

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