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प्रश्न
How will you differentiate between a convex and a concave lens by looking at
- a distant object,
- a printed page?
Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of:
- object distance, and
- magnification.
उत्तर १
- On seeing a distant object through the lens, if its inverted image is seen, then the lens is convex, and if the upright image is seen, then the lens is concave.
- On keeping the lens near a printed page, if the letters appear magnified, then the lens is convex, and if the letters appear diminished, then the lens is concave.
उत्तर २
| Sr. No. | Basis | Convex lens | Concave lens |
| 1. | Object distance | As long as the item is within the focal length (i.e., closer to the lens than it is to the focal length), the lens will make a virtual image. | When you look at something through a concave lens, the image is always on the same side of the lens as the item, no matter how far away it is. |
| 2. | Magnification | When there is a virtual image (an item within the focal length) and a convex lens, the image stands up and is magnified (magnification > 1). | When you look through a concave lens, the picture you see is always straight up but smaller (magnification < 1). |
संबंधित प्रश्न
Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.
If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system ?
Where must the object be placed for the image formed by a converging lens to be:
real, inverted and larger than the object?
An illuminated object is placed at a distance of 20 cm from a converging lens of focal length 15 cm. The image obtained on the screen is:
(a) upright and magnified
(b) inverted and magnified
(c) inverted and diminished
(d) upright and diminished
If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 19 cm from the lens, the image formed is slightly larger than object. The approximate focal length of the lens is ______.
What type of image is always made by a concave lens?
An object is placed 10 cm from a lens of focal length 5 cm. Draw the ray diagrams to show the formation of image if the lens is converging,
An object is placed 10 cm from a lens of focal length 5 cm. Draw the ray diagrams to show the formation of image if the lens is diverging.
Construct ray diagrams to illustrate the formation of a virtual image using a converging lens,
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
An object is 2 m from a lens which forms an erect image one-fourth (exactly) the size of the object. Determine the focal length of the lens. What type of lens is this?
What type of lens is used to correct
myopia?
State whether the following statement is true or false:
Short-sightedness can be cured by using a concave lens.
- Name the lens which always forms an erect and virtual image.
- State whether the image in part (a) is magnified or diminished.
At what distance from a concave lens of focal length 20 cm a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens? Also calculate the size of the image formed.
Draw a ray diagram to justify your answer for the above situation and label it.
An object is placed at a distance 24 cm in front of a convex lens of focal length 8 cm.
(i) What is the nature of the image so formed?
(ii) Calculate the distance of the image from the lens.
(iii) Calculate the magnification of the image.
Choose the correct alternative and rewrite the following:
Inside water, an air bubble behaves ....................
State three characteristics of the image of an extended source, formed by a concave lens.
Copy the following figure and complete it to show the formation of the image of the object AB. Name the lens used in the figure.
If the power of a lens is -4.0 D, then it means that the lens is a ______.
