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प्रश्न
Explain the working of an astronomical telescope using refraction of light.
उत्तर
The astronomical telescope consists of two lenses: objective and eyepiece. Objective has larger focal length and diameter to accommodate maximum amount of light coming from the far away (astronomical) objects. A parallel beam of rays from an astronomical object is made to fall on the objective lens of the telescope. It forms a real, inverted and diminished image A'B' of the object. The eyepiece is so adjusted that A'B' lies just at the focus of the eye piece. Therefore, a highly magnified image of the object is formed at infinity. The same has been shown in the figure below.
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संबंधित प्रश्न
Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.
If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system ?
Where must the object be placed for the image formed by a converging lens to be:
real, inverted and larger than the object?
List some things that concave lens and concave mirror have in common.
If the image formed by a lens is always diminished and erect, what is the nature of the lens?
Which type of lenses are:
thinner in the middle than at the edges?
A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.
The power of a concave lens is 10 D and that of a convex lens is 6 D. When these two lenses are placed in contact with each other, the power of their combination will be :
(a) +16 D
(b) +4 D
(c) −16 D
(d) −4 D
Name one of the common defects of vision and the type of lens used to remove it.
What kind of lens is used to correct
short-sightedness
An object is placed on the axis of a lens. An image is formed by refraction in the lens. For all positions of the object on the axis of the lens, the positions of the image are always always between the lens and the object.State three characteristics of the image.
- Name the lens which always forms an erect and virtual image.
- State whether the image in part (a) is magnified or diminished.
How will you differentiate between a convex and a concave lens by looking at
- a distant object,
- a printed page?
At what distance from a concave lens of focal length 20 cm a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens? Also calculate the size of the image formed.
Draw a ray diagram to justify your answer for the above situation and label it.
If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it?
A student obtained clear image of window grills on the screen. But the teacher told him to get the image of a tree far away, instead of window. To get a clear image, the lens must be ............................
Draw neat diagram to show the
Divergent action of concave lens
A concave lens has a focal length 30 cm. Find the position and magnification (m) of the image for an object placed in front of it at distance 30 cm. State whether the image is real or virtual?
An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm.
(i) Use the lens formula to find the distance of the image from the lens.
(ii) List four characteristics of the image (nature, position, size, erect/inverted) formed by the lens in this case.
(iii) Draw a ray diagram to justify your answer of the part (ii).
A parallel, oblique beam of light falls on a concave lens. Draw a diagram to show refraction of light through the lens.
