Advertisements
Advertisements
प्रश्न
The power of convex lens of focal length 20 cm is ______.
विकल्प
+5.0 D
0.20 D
-5.0 D
0.5 D
Advertisements
उत्तर
The power of convex lens of focal length 20 cm is +5.0 D.
Explanation:
Given: Focal length = f = 20 cm = 0.2 m
Power of the lens = P = ?
P = `1/("f"("m"))`
= `1/0.2`
= 5 D
The power of the lens is 5 D.
APPEARS IN
संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2.5 D.
Define the power of a lens.
What does sign of power (+ve or –ve) indicate?
State power of a lens S.I. unit.
Define 1 dioptre of power of a lens.
Find the power of a concave lens of focal length 2m.
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.
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.
Which type of lens has (a) a positive power, and (b) a negative power?
Which has more power : a thick convex lens or a thin convex lens, made of the same glass? Give reason for your choice.
A converging lens has focal length of 50 mm. What is the power of the lens?
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?
The power of a combination of two lenses X and Y is 5 D. If the focal length of lens X be 15 cm :
(a) calculate the focal length of lens Y.
(b) state the nature of lens Y.
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 is the unit of power of a lens? Define the unit of power of a lens.
How does the power of a lens change if its focal length is doubled?
The power of a lens is + 1.0 D is :
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.
Find the radius of curvature of the convex surface of a plano-convex lens, whose focal length is 0.3 m and the refractive index of the material of the lens is 1.5.
A normal eye is not able to see objects closer than 25 cm because
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
A 5.0 diopter lens forms a virtual image which is 4 times the object placed perpendicularly on the principal axis of the lens. Find the distance of the object from the lens.
A diverging lens of focal length 20 cm and a converging lens of focal length 30 cm are placed 15 cm apart with their principal axes coinciding. Where should an object be placed on the principal axis so that its image is formed at infinity?
Surabhi from std. X uses spectacle. The power of the lenses in her spectacle is 0.5 D.
Answer the following questions from the given information:
- Identify the type of lenses used in her spectacle.
- Identify the defect of vision Surabhi is suffering from.
- Find the focal length of the lenses used in her spectacle.
The power of a lens is +2.0 D. Find its focal length and state the kind of lens.
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.
Find the power of a convex lens of focal length of + 25 cm.
Power of a lens is – 4D, then its focal length is
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 |
An object is placed in front of a converging lens. Obtain the conditions under which the magnification produced by the lens is
- negative and
- positive.
The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is ______ cm.
An object is kept at a distance of 1m from a lens of power +2D:
- Identify the type of lens.
- Calculate its focal length and distance of the image formed.
In what unit is the power of a lens expressed?
