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प्रश्न
: Object near the lens : : ______ : 
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उत्तर
: Object near the lens : : Object at focus :
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संबंधित प्रश्न
If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens, the shape of the image of this object on the screen would be:
(a)
(b)
(c)
(d)
Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :
| S. No. | Object-Distance u (cm) |
Image-Distance v (cm) |
| 1 | –100 | +25 |
| 2 | –60 | +30 |
| 3 | –40 | +40 |
| 4 | –30 | +60 |
| 5 | –25 | +100 |
| 6 | –15 | +120 |
(a) What is the focal length of the convex lens? Give reason to justify your answer.
(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?
(c) Select an appropriate scale and draw a ray diagram for the observation at S.No. 2. Also find the approximate value of magnification.
A beam of light travelling in air is incident of water. Draw a ray-diagram indicating the change in its path in water.
A ray of light travelling in water emerges into air. Draw a ray-diagram indicating the change in its path.
If an object is placed at the focus of a convex lens, where is the image formed?
List some things that convex lens and concave mirror have in common.
Calculate the focal length of a convex lens which produces a virtual image at a distance of 50 cm of an object placed 20 cm in front of it.
If the object is moved to a point only 3 cm away from the lens, what is the new position, height and nature of the image?
What kind of lens can form:
am erect diminished image?
The focal lengths of four convex lenses P, Q, R and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S
The given below figure shows an object OA and its image IB formed by a lens
. 
draw suitable rays to locate the lens and its focus.
In the following cases, where must an object be placed in front of a convex lens so that the image formed is at infinity?
List four properties of the image formed by a convex mirror.
An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find (i) the position (ii) the magnification and (iii) the nature of the image formed.
Where must a point source of light be placed in front of a convex lens so as to obtain a parallel beam of light?
A lens always forms an image between the object and the lens.
A lens always forms an image between the object and the lens.
Answer the following question.
List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining an image of a distant object on a screen.
State the position of object, position of image, nature of image when: Convex lens is used as objective lens of photographic camera.
What happens to the image formed by a convex lens if its lower part is blackened?
Distinguish between:
Concave lens and Convex Lens
