To find-the image-distance for varying object-distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that he gradually moves the object towards the lens and each time focuses its image of the screen.
In which direction - towards or away from the lens, does he move the screen to focus the object?
What happens to the size of the image - does it increase or decrease?
What happen when he moves the object very close to the lens?
CBSE DELHI - SET 2 2015
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The position of the object moves away from the lens, as the student moves the object towards the lens. The screen should be moved away from the lens in order to obtain a sharp image.
When the object is moved near the lens, size of the image increases.
When the object is moved very close to the lens, it can be assumed to be placed between the focus and the optical centre. Then, the image formed is virtual, erect and enlarged.
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An object is placed at a distance of 12cm in front of a concave mirror of radius of curvature 30cm. List four characteristics of the image formed by the mirror.
Draw a ray diagram to show the formation of a real magnified image by a convex lens. (In your sketch the position of object and image with respect to the principal focus of lens should be shown clearly).
Explain with a suitable diagram, how a concave mirror converges a parallel beam of light rays. Mark clearly the pole, focus and centre of curvature of concave mirror in this diagram.
Draw a ray diagram to show the formation of a virtual magnified image of an object by a convex lens. In your diagram, the position of object and image with respect to the principal focus should be shown clearly.
“A concave mirror of focal length ‘f’ can form a magnified erect as well as an inverted image of an object placed in front of it.” Justify this statement stating the position of the object with respect to the mirror in each case for obtaining these images.