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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
A student is using a convex lens of focal length 18 cm to study the image formation by it for the various positions of the object. He observes that when he places the object at 27 cm, the location of the image is at 54 cm on the other side of the lens. Identify from the following diagram the three rays that are obeying the laws of refraction and may be used to draw the corresponding ray diagram.
(A) 1, 2 and 4
(B) 1, 3 and 5
(C) 2, 4 and 5
(D) 2, 3 and 4
An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre 'O' of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical 'O', principal focus F and height of the image on the diagram.
Study the given ray diagrams and select the correct statement from the following:
(A) Device X is a concave mirror and device Y is a convex lens, whose focal lengths are 20 cm and 25 cm respectively.
(B) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 10 cm and 25 cm respectively.
(C) Device X is a concave lens and device Y is a convex mirror, whose focal lengths are 20 cm and 25 cm respectively.
(D) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.
Where should an object be placed so that a real and inverted image of the same size as the object is obtained using a convex lens?
A 1 cm high object is placed at a distance of 2f from a convex lens. What is the height of the image formed?
What is a lens?
A convex lens of focal length 8 cm forms a real image of the same size as the object. The distance between object and its image will be:
An object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image.
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?
What type of images can a convex lens make?
A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
(a) +10 cm
(b) +20 cm
(c) −10 cm
(d) −20 cm
A lens forms an inverted image of an object. Name the kind of lens.
Draw neat diagram to show the
Convergent action of a convex 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
State the position of object, position of image, nature of image when: Convex lens is used in observing biological specimens.
Why do we say that the ‘2F’ and ‘F’ points of a convex lens can be regarded as a sort of ‘turning points’ as far as the nature of the image formed by it is concerned?
Draw a ray diagram to illustrate the determination of the focal length of a convex lens using an auxiliary plane mirror.
Differentiate convex lens and concave lens.
- 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.
Distinguish between:
Concave lens and Convex Lens
