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प्रश्न
Draw a ray diagram to show how a converging lens can form an image of the sun. Hence give a reason for the term ‘burning glass’ for a converging lens used in this manner.
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उत्तर
The sun is at infinity, so the convex lens forms its image at the second focal point, which is real and very much diminished in size.
While using the convex lens as burning glass, the rays of light from the sun (at infinity) are brought to focus on a piece of paper kept at the second focal plane of the lens. Due to the sufficient heat of the sun's rays, the paper burns. Hence, this lens is termed 'burning glass'.
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संबंधित प्रश्न
A lens forms an upright and diminished image of an object when the object is placed at its focal point. Name the lens and draw a ray diagram to show the image formation.
Draw a ray diagram to show how a converging lens can form a real and enlarged image of an object.
An object is placed at a distance 5 cm from a convex lens of focal length 10 cm. The image formed is virtual, upright and _____.
For the object placed between the optical centre and focus of a convex lens, the image is ______.
Which of the following lens would you prefer to use while reading small letters found in a dictionary?
An object is placed at a distance 20cm from a convex lens of focal length 10cm. Find the image distance and nature of the image.
An object of height 3cm is placed at 10cm from a concave lens of focal length 15cm. Find the size of the image.
Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?
Draw ray diagrams showing the image formation by a convex lens when an object is placed
- between optical centre and focus of the lens
- between focus and twice the focal length of the lens
- at twice the focal length of the lens
- at infinity
- at the focus of the lens
Complete the following table based on image formation by convex lens:
| Position of Object | Position of Image | Nature of Image |
| At infinity | (a) ______ | Real and inverted and highly diminished image |
| Beyond 2F1 | (b) ______ | (c) ______ |
| At 2F1 | (d) ______ | Real, inverted, same size (as object) image |
| Between F1 and 2F1 | Beyond 2F2 | (e) ______ |
| At focus F1 | (f) ______ | Real, inverted and highly enlarged image |
