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प्रश्न
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.
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उत्तर
1) The power is positive hence the convex lens
2) Hypermetropia
3) `"P" =1/"F"`
`"f" = 1/"P" = 1/0.5 = 2 "m"`
= 200 cm
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संबंधित प्रश्न
What is meant by a power of a lens? Define its SI unit.
State power of a lens S.I. unit.
How unit of power related to focal length of a lens?
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
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
Which one of the following materials cannot be used to make a lens?
Name the physical quantity whose unit is dioptre.
Which type of lens has (a) a positive power, and (b) a negative power?
How is the power of a lens related to its 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.
A converging lens has focal length of 50 mm. What is the power of the lens?
The power of a lens is + 0.2 D. Calculate its focal length.
The power of a lens is, −2 D. What is its focal length?
An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, −10 dioptres. Find the size of the image.
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?
The power of a lens is +2.0D. Its focal length should be :
Define the term focal length of a lens.
State the condition for the following a lens has both its focal lengths equal .
The power of a lens is + 1.0 D is :
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.
Define power of a lens. Write its units. Deduce the relation `1/f =1/f_1 +1/f_2`for two thin lenses kept in contact coaxially.
Consider three converging lenses L1, L2 and L3 having identical geometrical construction. The index of refraction of L1 and L2 are \[\mu_1 \text{ and } \mu_2\] respectively. The upper half of the lens L3 has a refractive index \[\mu_1\] and the lower half has \[\mu_2\] following figure . A point object O is imaged at O1 by the lens L1 and at O2 by the lens L2placed in same position. If L3 is placed at the same place,
(a) there will be an image at O1
(b) there will be an image at O2.
(c) the only image will form somewhere between O1 and O2
(d) the only image will form away from O2.
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?
Which lens has more power a thick lens or a thin lens?
The following diagram shows the object O and the image I formed by a lens. Copy the diagram and on it mark the positions of the lens LL’ and focus (F). Name the lens.
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.
If the lens is of focal length 25 cm. Calculate the power of the lens.
If there is a convex lens of focal length 75 cm and a concave lens of focal length 40 cm, then calculate their combined power and combined focal length.
If focal length of a convex lens is 20 cm at what is the power of the lens?
According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______.
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 |
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.
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?
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.
The lens of power + 1·0 D is ______.
In what unit is the power of a lens expressed?
