Advertisements
Advertisements
प्रश्न
If focal length of a convex lens is 20 cm at what is the power of the lens?
The focal length of a convex lens is 20 cm. What is its power?
Advertisements
उत्तर
Given: Focal length (f) = 20 cm = 0.2 m
To find: Power of the lens (P)
Formula: P = `1/("f"("m"))`
Calculation: From formula,
P = `1/0.2`
= 5 D
∴ The power of the convex lens is 5 D.
संबंधित प्रश्न
What is meant by a power of a lens? Define its SI unit.
What does sign of power (+ve or –ve) indicate?
Find the power of a concave lens of focal length 2m.
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?
What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
(a) At what distance should the lens be held from the figure in order to view the squares distinctly with the maximum possible magnifying power?
(b) What is the magnification in this case?
(c) Is the magnification equal to the magnifying power in this case? Explain.
Ranbir claims to have obtained an image twice the size of the object with a concave lens. Is he correct? Give a reason for your answer.
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
A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens
Name the physical quantity whose unit is dioptre.
Which type of lens has (a) a positive power, and (b) a negative power?
Which of the two has a greater power: a lens of short focal length or a lens of large focal length?
Which has more power : a thick convex lens or a thin convex lens, made of the same glass? Give reason for your choice.
What is the power of a convex lens lens whose focal length is 80 cm?
The power of a lens is, −2 D. What is its focal length?
What is the nature of a lens whose power is, −4 D?
What is the unit of power of a lens? Define the unit of power of a lens.
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:
State the condition for the following a lens has both its focal lengths equal .
How is the power of a lens related to its focal length?
On reducing the focal length of a lens, its power ______.
The power of a lens is + 1.0 D is :
Express the power (with sign) of a concave lens of focal length 20 cm.
A convex lens produces a double size real image when an object is placed at a distance of 18 cm from it. Where should the object be placed to produce a triple size real image?
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?
How is accommodation produced?
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.
Match the following:
| Column - I | Column - II | ||
| 1 | Retina | a | Path way of light |
| 2 | Pupil | b | Far point comes closer |
| 3 | Ciliary muscles | c | near point moves away |
| 4 | Myopia | d | Screen of the eye |
| 5 | Hypermetropia | e | Power of accommodation |
The above lens has a focal length of 10 cm. The object of height 2 mm is placed at a distance of 5 cm from the pole. Find the height of the image.
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
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 power of convex lens of focal length 20 cm is ______.
In what unit is the power of a lens expressed?
