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प्रश्न
Write two important limitations of a refracting telescope over a reflecting-type telescope.
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उत्तर
Limitations of refracting telescope over reflecting type telescope:
- Refracting telescope suffers from chromatic aberration as it uses large-sized lenses.
- The image formed by refracting telescope is less bright than the image formed by the reflecting type telescope due to some loss of light by reflection at the lens and by absorption.
- The resolving power of refracting telescope is less than the resolving power of the reflecting type telescope as the mirror of the reflecting type telescope has a large diameter.
- The requirements of big lenses tend to be very heavy and therefore difficult to make and support by their edges.
- It is also difficult and expensive to make such large-sized lenses.
Notes
Students should refer to the answer according to their questions.
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संबंधित प्रश्न
A small telescope has an objective lens of focal length 140 cm and an eyepiece of focal length 5.0 cm. What is the magnifying power of the telescope for viewing distant objects when
- the telescope is in normal adjustment (i.e., when the final image is at infinity)?
- the final image is formed at the least distance of distinct vision (25 cm)?
You are given three lenses of power 0.5 D, 4 D, and 10 D to design a telescope.
1) Which lenses should be used as objective and eyepiece? Justify your answer.
2) Why is the aperture of the objective preferred to be large?
Describe briefly the two main limitations and explain how far these can be minimized in a reflecting telescope ?
Draw a labeled ray diagram of a reflecting telescope. Mention its two advantages over the refracting telescope.
A Galilean telescope is 27 cm long when focussed to form an image at infinity. If the objective has a focal length of 30 cm, what is the focal length of the eyepiece?
Define the term ‘resolving power of a telescope’.
Draw a ray diagram of astronomical telescope for the final image formed at infinity.
Draw a ray diagram for the formation of image of an object by an astronomical telescope, in normal adjustment. Obtain the expression for its magnifying power.
The magnifying power of an astronomical telescope in normal adjustment is 2.9 and the objective and the eyepiece are separated by a distance of 150 cm. Find the focal lengths of the two lenses.
Assertion: An astronomical telescope has an objective lens having large focal length.
Reason: Magnifying power of an astronomical telescope varies directly with focal length of the objective lens.
