Advertisements
Advertisements
प्रश्न
Write scientific reason.
Adults need bifocal lens spectacle.
Advertisements
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.
APPEARS IN
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
Where should an object be placed in front of a convex lens so as to obtain its virtual, erect and magnified image?
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image?
What type of lens would you use as a magnifying glass? How close must the object be to the lens?
What is a lens?
With the help of a labelled diagram explain how a convex lens converges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the convex lens on the diagram.
A convex lens has a focal length of 10 cm. At which of the following position should an object be placed so that this convex lens may act as a magnifying glass?
(a) 15 cm
(b) 7 cm
(c) 20 cm
(d) 25 cm
An object is placed f and 2f of a convex lens. Which of the following statements correctly describes its image?
(a) real, larger than the object
(b) erect, smaller than the object
(c) inverted, same size as object
(d) virtual, larger than the object
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
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:
(a) 8 cm
(b) 16 cm
(c) 24 cm
(d) 32 cm
What type of lens is used to correct
hypermetropia
Study the diagram below.
what are the points O, O’ called?
A converging lens forms the image of an object placed in front of it, beyond 2F2 of the lens. Draw a ray diagram to show the formation of the image.
A lens forms an upright and magnified image of an object. Name the lens.
In the following cases, where must an object be placed in front of a convex lens so that the image formed is at infinity?
When you focus the image of a distant flag, whose shape is given below, on a screen using a convex lens, the shape of the image as it appears on the screen is
(A)
(B)
(C)
(D)
An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm.
(i) At what distance from the mirror should a screen be placed in order to obtain a sharp image?
(ii) Find the size of the image.
(iii) Draw a ray diagram to show the formation of the image in this case.
What is the difference between a double convex and a bi-convex lens?
Convex lens is also known as ______.
