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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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उत्तर
Since the object is at infinity, the image will be formed at the focus. The image distance will be equal to the focal length of the lens. Therefore, the focal length of the lens is 20 cm.
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संबंधित प्रश्न
We can obtain an enlarged and erect image by a convex mirror.
A concave mirror always forms a real image.
A concave lens produces an image 20 cm from the lens of an object placed 30 cm from the lens. The focal length of the lens is:
(a) 50 cm
(b) 40 cm
(c) 60 cm
(d) 30 cm
An optical device has been given to a student and he determines its focal length by focusing the image of the sun on a screen placed 24 cm from the device on the same side as the sun. Select the correct statement about the device.
(A) Convex mirror of focal length 12 cm
(B) Convex lens of focal length 24 cm
(C) Concave mirror of focal length 24 cm
(D) Convex lens of focal length 12 cm
AB and CD, two spherical mirrors, from parts of a hollow spherical ball with its centre at O as shown in the diagram. If arc AB = `1/2` arc CD, what is the ratio of their focal lengths? State which of the two mirrors will always form virtual image of an object placed in front of it and why.
Explain the following term:
Incident ray
Draw diagram/diagrams to show them.
Upto what maximum distance from the pole the image in a convex mirror can be obtained? what will be the location of object then ?
Select the correct option:
A concave mirror is made by cutting a portion of a hollow glass sphere of radius 30 cm. The focal length of the concave mirror is:
AB is the object, A'B' is the image, and MM' is the position of the mirror. Complete the ray diagram showing the formation of the image and find the focal length of the mirror.
The following figure shows a concave mirror with its pole (P), focus (F), and center of curvature (C). Draw a ray diagram to show the formation of the image of an object AB by the concave mirror.
The spherical mirror used in a beauty parlour as make-up mirror is _______.
What is the difference between virtual images of an object formed by a concave mirror and a convex mirror?
For a spherical mirror, ______ is true.
The image formed in a plane mirror is always inverted.
A converging lens of focal length f is placed at a distance 0.3 m from an object to produce an image on a screen 0.9 m from the lens. With the object and the screen in the same positions, an image of the object could also be produced on the screen by placing a converging lens of focal length.
In normal adjustment, for a refracting telescope, the distance between objective and eye piece is 30 cm. The focal length of the objective, when the angular magnification of the telescope is 2, will be ______.
