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Question
State the condition under which a large magnification can be achieved in an astronomical telescope.
Solution 1
Condition under which a large magnification can be achieved in an astronomical telescope:
In astronomical telescope, the light is incident from infinity on the objective lens and it forms image at the focus of the objective lens and for large magnification the length between the lens is so adjusted that the final image is formed at the least distance of the distinct vision from the eyepiece
Magnification of astronomical telescope is
\[(M . P )_\max = - \frac{f_o}{f_e}(1 + \frac{f_e}{d})\] To have large magnification power, \[f_o\] must be large as possible and \[f_e\] must be as small as possible.
Solution 2
By increasing the focal length of objective lens and at the same time keeping the focal length of eye peice minimum we can increase the magnifying power of telescope
RELATED QUESTIONS
Draw a schematic ray diagram of a reflecting telescope showing how rays coming from a distant object are received at the eyepiece.
Why should the objective of a telescope have large focal length and large aperture? Justify your answer.
Draw a ray diagram depicting the formation of the image by an astronomical telescope in normal adjustment.
Draw a labelled ray diagram of an image formed by a refracting telescope with the final image formed at infinity. Derive an expression for its magnifying power with the final image at infinity
With regard to an astronomical telescope of refracting type~ state how you will increase its:
1) magnifying power
2) resolving power
Write two important limitations of a refracting telescope over a reflecting-type telescope.
Draw a ray diagram of a refracting astronomical telescope when final image is formed at infinity. Also write the expression for its angular magnification (magnifying power).
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.
In an astronomical telescope in normal adjustment, a straight black line of length L is drawn on the objective lens. The eyepiece forms a real image of this line whose length is ЁЭСЩ. What is the angular magnification of the telescope?
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 | |||
