Advertisements
Advertisements
प्रश्न
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.
Advertisements
उत्तर
Focal length of the convex lens, f1 = 30 cm
Focal length of the concave lens, f2 = −20 cm
Focal length of the system of lenses = f
The equivalent focal length of a system of two lenses in contact is given as:
`1/"f" = 1/"f"_1 + 1/"f"_2`
`1/"f" = 1/30 - 1/20`
`1/"f" = (2 - 3)/60`
`1/"f" = -1/60`
∴ f = −60 cm
Hence, the focal length of the combination of lenses is 60 cm. The negative sign indicates that the system of lenses acts as a diverging lens.
संबंधित प्रश्न
State power of a lens S.I. unit.
(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 power of a lens is, −2 D. What is its focal length?
A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact with each other. What is the :
(a) power of this combination of lenses?
(b) focal length of this combination of lenses?
What do you understand by the power of a lens? Name one factor on which the power of a lens depends.
State the condition for the following a ray passes undeviated through the lens .
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 :
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.
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?
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.
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.
If the lens is of focal length 25 cm. Calculate the power of the lens.
Find the power of a convex lens of focal length of + 25 cm.
According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______.
The focal length of a double convex lens is equal to the radius of curvature of either surface. What is the refractive index of its material?
