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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 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?
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Why should the objective of a telescope have large focal length and large aperture? Justify your answer.
Describe briefly the two main limitations and explain how far these can be minimized in a reflecting telescope ?
"A telescope resolves whereas a microscope magnifies." Justify this statement ?
A small telescope has an objective lens of focal length 150 cm and an eye piece of focal length 5 cm. If this telescope is used to view a 100 m high tower 3 km away, find the height of the final image when it is formed 25 cm away from the eye piece.
Draw a labelled ray diagram showing the formation of an image by a refracting telescope when the final image lies at infinity.
Define the term ‘resolving power of a telescope’.
A small telescope has an objective lens of focal length 140 cm and an eyepiece of focal length 5.0 cm. Find the magnifying power of the telescope for viewing distant objects when
- the telescope is in normal adjustment,
- the final image is formed at the least distance of distinct vision.
Read the following paragraph and answer the questions.
| A number of optical devices and instruments have been designed and developed such as periscope, binoculars, microscopes and telescopes utilising the reflecting and refracting properties of mirrors, lenses and prisms. Most of them are in common use. Our knowledge about the formation of images by the mirrors and lenses is the basic requirement for understanding the working of these devices. |
- Why the image formed at infinity is often considered most suitable for viewing. Explain
- In modern microscopes, multicomponent lenses are used for both the objective and the eyepiece. Why?
- Write two points of difference between a compound microscope and an astronomical telescope
OR
Write two distinct advantages of a reflecting type telescope over a refracting type telescope.
A small telescope has an objective of focal length 140 cm and an eye piece of focal length 5.0 cm. The magnifying power of telescope for viewing a distant object?
