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प्रश्न
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.
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उत्तर
The illustration displays an astronomy telescope used to provide angular magnification of distant objects. It sports a big diameter objective lens with a long focal length. The diameter and focal length of the eyepiece are both smaller than those of the objective lens. When light from a distant object enters the objective, an actual image is formed in the tube at its second focal point. The eyepiece enlarges this image, resulting in the final inverted image. The "tube length" or distance between the objective and the eyepiece, is the sum of the focal lengths of the two lenses when their innermost points meet.
The angle “β” that the picture subtends at the eye compared to the angle “α” that the object subends at the lens is the magnifying power or m.
`m = (beta/alpha)`
`beta = tanbeta = h/f_e`
Where h is image height and fe is focal length of eyepiece.
`alpha = tanalpha = h/f_o`
Where fo is focal length of objective lens.
Hence, we get magnifying power m as,
`m = (h"/"f_e)/(h"/"f_o) = f_o/f_e`
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संबंधित प्रश्न
- 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?
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 ?
Write two important limitations of a refracting telescope over a reflecting-type telescope.
An astronomical telescope is to be designed to have a magnifying power of 50 in normal adjustment. If the length of the tube is 102 cm, find the powers of the objective and the eyepiece.
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?
A lady cannot see objects closer than 40 cm from the left eye and closer than 100 cm from the right eye. While on a mountaineering trip, she is lost from her team. She tries to make an astronomical telescope from her reading glasses to look for her teammates. (a) Which glass should she use as the eyepiece? (b) What magnification can she get with relaxed eye?
Define the term ‘resolving power of a telescope’.
Draw a ray diagram of Astronomical Telescope for the final image formed at infinity
Read the passage given below and answer the question that follows.
| There are two types of optical instruments: Microscopes and Telescopes. Microscopes are used to magnify very tiny objects whereas telescopes are used to study distant objects. Both of them deploy convex lenses. In his telescope, Newton used a large parabolic mirror to collect light from the stars and reduce aberrations. |
- Rohit observed the launch of Chandrayan 3 with the help of an optical instrument. Name the instrument used by him.
- State any one advantage of a reflecting telescope over a refracting telescope.
- Which instrument is used to study the structure of a virus?
- What is the ability of an optical instrument to form enlarged images called?
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What is the difference between a compound microscope and an astronomical telescope (refracting type), as far as their lenses are concerned?
Useful Constants & Relations:
| 1 | Charge of a proton | e | 1.6 × 10-19 C |
| 2 | Speed of light in vacuum | c | 3 × 108 ms-1 |
| 1 u = 931 MeV | |||
