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प्रश्न
A concave mirror forms a virtual image of size twice that of the object placed at a distance 5 cm from it.
Find : (a) the focal length of the mirror (b) position of image
उत्तर
m = `"I"/"O" = 20/"O" = 2`
∵ m = `-"v"/"u"`
∴ `-"v"/"u" = 2`
∴ -v = 2u
∵ u = -5 cm
∴ v = 10 cm
Hence , the position of the image is 10 cm behind the mirror.
From mirror formula ,
`1/"f" = 1/"v" + 1/"u"`
∴ `1/"f" = 1/10 + 1/(-5) = 1/10 - 1/5`
∴ f = -10 cm
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संबंधित प्रश्न
A 50 cm tall object is at a very large distance from a diverging lens. A virtual, erect and diminished image of the object is formed at a distance of 20 cm in front of the lens. How much is the focal length of the lens?
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A student obtained on a screen the sharp image of a candle flame placed at the farther end of laboratory table using a concave mirror. For getting better value of focal length of the mirror, the teacher suggested to him to focus the sun. What should the student do?
(A) Should move the mirror away from the screen.
(B) Should move the mirror towards the screen.
(C) Should move the mirror and screen both towards the sun.
(D) Should move only the screen towards the sun.
Name the spherical mirror which (i) diverges (ii) converges the beam of light incident on it. Justify your answer by drawing a ray diagram in each case.
Define the terms focus and focal length of a concave mirror. Draw diagram to illustrate your answer.
Select the correct option:
A mirror forms a virtual image (diminished) of an object, whatever be the position of object:
If the real image of a candle flame formed by a lens is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens?
Size of image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/3rd of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?
Define the following terms in the context of a diverging mirror:
- Principal focus
- Focal length
Draw a labelled ray diagram to illustrate your answer.
