Advertisements
Advertisements
प्रश्न
Write two important limitations of a refracting telescope over a reflecting-type telescope.
Advertisements
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.
APPEARS IN
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)?
With regard to an astronomical telescope of refracting type~ state how you will increase its:
1) magnifying power
2) resolving power
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.
The eyepiece of an astronomical telescope has a focal length of 10 cm. The telescope is focussed for normal vision of distant objects when the tube length is 1.0. m. Find the focal length of the objective and the magnifying power of the telescope.
An astronomical telescope uses two lenses of powers 10 dioptres and 1 dioptre. If the final image of a distant object is formed at infinity, calculate the length of the telescope
Define the term ‘resolving power of a telescope’.
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.
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.
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.
