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प्रश्न
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.
उत्तर
Given:
Object distance, u =-20 cm
Image distance, v =-50 cm (Image is virtual.)
Applying lens formula, we get:
1/v- 1/u = 1/f (f = focal distance)
1/( -50)- 1/(-20) =1/f
or, 1/f = (-2+5)/100
or, 1/f =3/100
or, f = 100/3 = + 33.3 cm
Thus, the focal length of convex lens is 33.3 cm.
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संबंधित प्रश्न
An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
A beam of light travelling in a rectangular glass slab emerges into air. Draw a ray-diagram indicating the change in its path.
Where should an object be placed in order to use a convex lens as a magnifying glass?
Define principal axis, principal focus and focal length of a convex lens.
How could you find the focal length of a convex lens rapidly but approximately?
In order to obtain a real image twice the size of the object with a convex lens of focal length 15 cm, the object distance should be:
(a) more than 5 cm but less than 10 cm
(b) more than 10 cm but less than 15 cm
(c) more than 15 cm but less than 30 cm
(d) more than 30 cm but less than 60 cm
Study the diagram given below.
- Name the lens LL’.
- What are the points O and O’ called?
- Complete the diagram to form the image of the object AB.
- State the three characteristics of the image.
- Name a device in which this action of lens is used.
A lens forms an upright and magnified image of an object. Name the lens.
(a) What type of a lens can be used as a magnifying glass?
(b) Show by a ray diagram the formation of a real image by simple magnifying lens.
State the position of object, position of image, nature of image when: Convex lens is used as objective lens of astronomical telescope.
