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प्रश्न
Describe briefly the two main limitations and explain how far these can be minimized in a reflecting telescope ?
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उत्तर
Two limitations of refractive telescope are:
1. The lens used in refractive telescope are expensive.
2. The lens used for making refracting telescope have chromatic aberration and distortions.
They can be minimised by using reflecting type telescope, which use concave mirror rather than a lens for the objective. Reflecting type telescope has the following advantages:
1. They are free from chromatic aberration as mirror is used instead of lens.
2. There is no problem for mechanical support because weight of mirror is much less than the weight of the lens. It can be supported easily.
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संबंधित प्रश्न
Draw a schematic ray diagram of a reflecting telescope showing how rays coming from a distant object are received at the eyepiece.
Draw a labeled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power.
A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal length 6.0 cm. What is the magnifying power of the telescope? What is the separation between the objective and the eyepiece?
- A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece of focal length 1.0 cm is used, what is the angular magnification of the telescope?
- If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.48 × 106 m, and the radius of lunar orbit is 3.8 × 108 m.
- For the telescope is in normal adjustment (i.e., when the final image is at infinity)? what is the separation between the objective lens and the eyepiece?
- If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens?
- What is the height of the final image of the tower if it is formed at 25 cm?
Why should the objective of a telescope have large focal length and large aperture? Justify your answer.
You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope ? Give reason
| Lenses | Power (D) | Aperture (cm) |
| L1 | 3 | 8 |
| L2 | 6 | 1 |
| L3 | 10 | 1 |
Define its magnifying power and write the expression for it?
(i) What is meant by resolving power of a telescope?
(ii) State any one method of increasing the resolving power of an astronomical telescope.
Define the term ‘resolving power of a telescope’.
