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प्रश्न
Why does obtaining the image of the sun on paper with the help of a concave mirror burn the paper?
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उत्तर
The rays from the Sun are parallel. When these rays fall on the concave mirror, they converge to a single point on the focal plane of the mirror. Thus, a lot of heat is produced at that point. Now, if a paper is placed at that point to get the image of the Sun, the paper gets burnt because of the huge amount of heat concentrated at that point.
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संबंधित प्रश्न
"A concave mirror of focal length 15 cm can form a magnified, erect as well as inverted image of an object placed in front of it." Justify this statement stating the position of the object with respect to the pole of the mirror in both the cases for obtaining the images.
A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to be ______.
An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.
To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions after reflection from the mirror. List two such rays and state the path of these rays after reflection in case of concave mirrors. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror.
If the focal length of a convex mirror is 25 cm, what is its radius of curvature?
Fill in the following blank with suitable word:
Parallel rays of light are reflected by a concave mirror to a point called the ..........
For what position of an object, a real and diminished image is formed by a concave mirror?
Explain why, a ray of light passing through the centre of curvature of a concave mirror gets reflected back along the same path.
Write down a formula for the magnification produced by a concave mirror.
in terms of height of object and height of image
A converging mirror forms a real image of height 4 cm of an object of height 1 cm placed 20 cm away from the mirror:
- Calculate the image distance.
- What is the focal length of the mirror?
A man holds a spherical shaving mirror of radius of curvature 60 cm, and focal length 30 cm, at a distance of 15 cm, from his nose. Find the position of image, and calculate the magnification.
What type of mirror should be used as a shaving mirror?
A student determines the focal length of a device 'X' by focusing the image of a distant object on a screen placed 20 cm from the device on the same side as the object. The device 'X' is
(a) Concave lens of focal length 10 cm
(b) Convex lens of focal length 20 cm
(c) Concave mirror of focal length 10 cm
(d) Concave mirror of focal length 20 cm
Answer the following question:
An object is placed at a distance of 30 cm from a concave lens of focal length 30 cm.
(i) Use the lens formula to determine the distance of the image from the lens.
(ii) List four characteristics of the image (nature, position, size, erect/inverted) in this case.
(iii) Draw a labelled diagram to justify your answer of the part (ii)
Study the following ray diagram and list two mistakes committed by the student while tracing it. Rectify these mistakes by drawing the correct ray diagram to show the real position and size of the image corresponding to the position of the object AB.
In which of the following, the image of an object placed at infinity will be highly diminished and point sized?
An image formed by a lens is erect. Such an image could be formed by a
The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?
A student wants to obtain an erect image of an object using a concave mirror of 10 cm focal length. What will be the distance of the object from mirror?
A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distance with these mirrors as shown in the following table.
| Case No. | Object-distance | Focal length |
| I | 45 cm | 20 cm |
| II | 30 cm | 15 cm |
| III | 20 cm | 30 cm |
Now answer the following questions:
(a) List two properties of the image formed in Case I.
(b) In which one of the cases given in the table, the mirror will form real image of same size and why?
(c) Name the type of mirror used by dentists. Given reason why do they use such type of mirrors.
OR
(c) Look at the table and identify the situation (object distance and focal length) which resembles the situation in which concave mirrors are used as shaving mirrors? Draw a ray diagram to show the image formation in this case.
