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प्रश्न
Write scientific reason.
Adults need bifocal lens spectacle.
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उत्तर
- The ability of the ciliary muscles near the eye lens to change the focal length of the lens decreases with age.
- As a result, sometimes adults suffer from both nearsightedness and farsightedness.
Therefore, adults need bifocal lens spectacle.
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संबंधित प्रश्न
When a ray of light enters from one medium to another having different optical densities it bends. Why does this phenomenon occur?
Describe with the help of a ray diagram the nature, size and position of the image formed when an object is placed at infinity (considerable distance) in front of a convex lens. State three characteristics of the image so formed.
What type of lens is shown in the diagram on the right? What will happen to the parallel rays of light? Show by completing the ray diagram.
State whether the convex lens has a real focus or a virtual focus.
A convex lens has a focal length of 10 cm. At which of the following positions should an object be placed so that this convex lens may act as a magnifying glass?
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
An object 2 cm tall is placed on the axis of a convex lens of focal length 5 cm at a distance of 10 m from the optical centre of the lens. Find the nature, position and size of the image formed. Which case of image formation by convex lenses is illustrated by this example?
If the object is moved to a point only 3 cm away from the lens, what is the new position, height and nature of the image?
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
Which of the object distances gives the biggest image?
Study the diagram below.
what are the points O, O’ called?
A lens forms an erect, magnified, and virtual image of an object.
- Name the type of lens.
- Draw a ray diagram to show the formation of the image.
- Where is the object placed in relation to the lens?
- Name the device which uses this principle.
A convex lens forms an image of an object equal to the size of the object. State two more characteristics of the image.
In the following cases, where must an object be placed in front of a convex lens so that the image formed is at infinity?
In the following cases, where must an object be placed in front of a convex lens so that the image formed is upright and enlarged?
Out of the five incident rays shown in the figure find the three rays that are obeying the laws of refraction and may be used for locating the position of image formed by a convex lens:
(A) 1, 2 and 3
(B) 2, 3 and 4
(C) 3, 4 and 5
(D) 1, 2 and 4
Yesh find out F1 and F2 of symmetric convex lens experimentally then which conclusion is true.
State the position of object, position of image, nature of image when: Convex lens is used as an erecting lens in terrestrial telescope.
Observe the given figure and answer the following questions.
- Where is the above type of lens construction used?
- What type of image is formed by an objective lens?
- What happens instead of placing at Fo if the object is placed in between O and Fo?
- In which type of microscope do you find the lens arrangement as shown in the following diagram?
- Write about the working and the use of this microscope.
