Advertisements
Advertisements
प्रश्न
Kavita from 10th is using spectacles. The power of the lenses in her spectacles is –2.5 dioptre. Answer the following questions:
1) Which lenses are used in her spectacles?
2) State the defect of vision Kavita is suffering from.
3) Find the focal length of the lenses used in her spectacles
Advertisements
उत्तर
1) Concave lens
2) Myopia or nearsightedness
3) `f = 1/D = 1/2.5 = 0.4 m`
APPEARS IN
संबंधित प्रश्न
State power of a lens S.I. unit.
Find the power of a concave lens of focal length 2m.
Find the focal length of a lens of power −2.0 D. What type of lens is this?
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
Name the physical quantity whose unit is dioptre.
Which of the two has a greater power: a lens of short focal length or a lens of large focal length?
How is the power of a lens related to its focal length?
The power of a lens is + 0.2 D. Calculate its focal length.
A doctor has prescribed a corrective lens of power, −1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Two lenses A and B have focal lengths of +20 cm and, −10 cm, respectively.
(a) What is the nature of lens A and lens B?
(b) What is the power of lens A and lens B?
(c) What is the power of combination if lenses A and B are held close together?
What do you understand by the power of a lens? Name one factor on which the power of a lens depends.
A converging lens has a focal length of 50 cm. The power of this lens is:
A diverging lens has a focal length of 0.10 m. The power of this lens will be:
Define the term focal length of a lens.
State the condition for the following a lens has both its focal lengths equal .
Express the power (with sign) of a concave lens of focal length 20 cm.
Name the type of lens whose power is positive.
The image of an object formed by a lens is real, inverted and of the same size as the object. If the image is at a distance of 40 cm from the lens, what is the nature and power of the lens ? Draw ray diagram to justify your answer.
How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for your answer.
Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:
(1) a blurred image on the wall of the laboratory.
(2) an erect image of the tree on the lens.
(3) no image as the screen has been removed
(4) an inverted image of the tree at the focus of the lens.
A normal eye is not able to see objects closer than 25 cm because
A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]
A symmetric double convex lens in cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4 D, the power a cut-lens will be
A symmetric double convex lens is cut in two equal parts by a plane containing the principal axis. If the power of the original lens was 4 D, the power of a divided lens will be
Consider the situation described in the previous problem. Where should a point source be placed on the principal axis so that the two images form at the same place?
A lens forms an upright and diminished image of an object, irrespective of its position. What kind of lens is this? Draw an outline ray diagram to show the formation of the image. State the position and one more characteristic of the image.
Complete the diagram to show the formation of the image of the object AB.
(i) Name the Lens LL’.
(ii) Where is the image of the object AB formed?
(iii) State three characteristics of the image.
A convex lens is of focal length 20 cm. Find its power.
Find the power of a convex lens of focal length of + 25 cm.
If focal length of a convex lens is 20 cm at what is the power of the lens?
Assertion and reasoning type
- Assertion: Myopia is due to the increase in the converging power of eye lens.
- Reason: Myopia can be corrected with the help of concave lens.
The focal length of a concave lens is 20 cm. The focal length of a convex lens is 25 cm. These two are placed in contact with each other. What is the power of the combination? Is it diverging, converging or undeviating in nature?
The lens of power + 1·0 D is ______.
