Advertisements
Advertisements
प्रश्न
Calculate the focal length of a corrective lens having power +2.5 D.
Advertisements
उत्तर
Solution: Data: Convex lens, P = +2.5 D, f = ?
P = 1/f
∴ 2.5 D = 1/f
∴ f = 1/2.5D = 0.4m = 40cm
The focal length of the lens is 40 cm.
APPEARS IN
संबंधित प्रश्न
Define the power of a lens.
How unit of power related to focal length of a lens?
A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
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.
The lens mentioned in 6(b) above is of focal length 25cm. Calculate the power of the lens.
What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
The focal length of a convex lens is 25 cm. What is its power?
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?
A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?
Fill in the following blank with suitable words :
The reciprocal of the focal length in metres gives you the _________ of the lens, which is measured in ___________.
A converging lens has a focal length of 50 cm. The power of this lens is:
The power of a lens is +2.0D. Its focal length should be :
The power of a lens is + 1.0 D is :
How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for 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.
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 thin converging lens is formed with one surface convex and the other plane. Does the position of image depend on whether the convex surface or the plane surface faces the object?
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 screen is placed a distance 40 cm away from an illuminated object. A converging lens is placed between the source and the screen and its is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens
How is accommodation produced?
The power of a lens is +2.0 D. Find its focal length and state the kind of 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.
Focal length : metre : : power of lens : _______
The power of the magnifying glass depends on the distance of the magnifying glass from object.
According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______.
The power of lens depends on the focal length of the lens
Increase in the converging power of eye lens cause ‘hypermetropia'
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.
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.
A point object is placed at O in front of a glass sphere as shown in figure.
Show the formation of the image by the sphere.
