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प्रश्न
Distinguish between:
Concave lens and Convex lens
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उत्तर
| Concave lens | Convex lens | |
| 1. | It is a diverging lens because it diverges the rays falling on it. | It is a converging lens because it converges the rays falling on it. |
| 2. | It is thin at the center and bulged at the edge. | It is thin at the edge and bulged at the centre. |
| 3. | The image formed by concave lens is always diminished and virtual. | The image formed by convex lens can be real as well as virtual. Also, the image formed can be diminished as well as magnified. |
| 4. | It has a virtual focus. | It has a real focus. |
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संबंधित प्रश्न
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen.
(a) In which direction-toward or away from the lens, does he move the screen to focus the image?
(b) How does the size of the image change?
(c) How does the intensity of the image change as the flame moves towards the lens?
(d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size?
Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :
| S. No. | Object-Distance u (cm) |
Image-Distance v (cm) |
| 1 | –100 | +25 |
| 2 | –60 | +30 |
| 3 | –40 | +40 |
| 4 | –30 | +60 |
| 5 | –25 | +100 |
| 6 | –15 | +120 |
(a) What is the focal length of the convex lens? Give reason to justify your answer.
(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?
(c) Select an appropriate scale and draw a ray diagram for the observation at S.No. 2. Also find the approximate value of magnification.
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.
Draw a labelled ray diagram to show how a ray of light is refracted when it passes:
from an optically denser medium into air.
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image?
You eye contains a convex lens. Why is it unwise to look at the sun?
An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
How would a pencil look like if you saw it through How would a pencil look like if you saw it through
A parallel oblique beam of light falls on a convex lens. Draw a diagram to show the refraction of light through the lens.
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.
Where is the image formed?
The given below figure shows an object OA and its image IB formed by a lens.
The given below figure shows an object OA and its image IB formed by a lens. State three characteristics of the image.
(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.
A convex lens forms an inverted image of size same as that of the object which is placed at a distance 60 cm in front of the lens. Find: The position of image
Draw a diagram to show the convergent action of a convex lens by treating it as a combination of glass block and two triangular glass prisms, with the aid of two parallel incident rays.
We can burn a piece of paper by focussing the sun rays by using a particular type of lens. Name the type of lens used for the above purpose. Draw a ray diagram to support your answer.
Convex lens is also known as ______.
