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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.
An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is:
(i) 12 cm from the lens
(ii) 6 cm from the lens
State one practical application each of the use of such a lens with the object in position (i) and (ii).
Which type of lenses are:
thinner in the middle than at the edges?
A ray of light is going towards the focus of a concave lens. draw a ray diagram to show the path of this ray of light after refraction through the lens.
An object lies at a distance of 2f from a concave lens of focal length f. Draw a ray-diagram to illustrate the image formation.
Construct ray diagrams to illustrate the formation of a virtual image using a converging lens,
When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object.
What is the focal length of lens A?
When a fork is seen through lenses A and B one by one, it appears as shown in the diagrams. What is the nature of (i) lens A, and (ii) lens B? Give reason for your answer.
An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Fine the position and nature of the image.
An object is placed on the axis of a lens. An image is formed by refraction in the lens. For all positions of the object on the axis of the lens, the positions of the image are always always between the lens and the object name the lens.
- Name the lens which always forms an erect and virtual image.
- State whether the image in part (a) is magnified or diminished.
A concave lens forms a magnified or diminished image depending on the distance of an object from it.
The diagrams showing the correct path of the ray after passing through the lens are:
 |
 |
| I | II |
 |
 |
| III | IV |
Explain the working of an astronomical telescope using refraction of light.
A virtual diminished image is formed when an object is placed between the optical centre and the principal focus of a lens.
(i) Name the type of lens which forms the above image.
(ii) Draw a ray diagram to show the formation of the image with the above stated characteristics.
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.
Draw images in case of a concave lens when the object is at any point on the principal axis between the lens and infinity.
Distinguish between Concave lens and Convex Lens.
Distinguish between:
Concave Lens and Convex Lens
