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प्रश्न
Focal length : metre : : power of lens : _______
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उत्तर
Focal length : metre : : power of lens : dioptre
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संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2D.
Calculate the focal length of a corrective lens having power +2.5 D.
What does sign of power (+ve or –ve) indicate?
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.
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.
A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each 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
Which one of the following materials cannot be used to make a lens?
Which of the two has a greater power: a lens of short focal length or a lens of large focal length?
How is the power of a lens related to its focal length?
What is the power of a convex lens of focal length 0.5 m?
What is the power of a convex lens lens whose focal length is 80 cm?
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?
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 ___________.
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
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 do you understand by the power of a lens?
The power of a lens is +2.0D. Its focal length should be :
State the condition for the following a lens has both its focal lengths equal .
The power of a lens is + 1.0 D is :
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
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 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.
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?
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.
A convex lens is of focal length 20 cm. Find its power.
If the lens is of focal length 25 cm. Calculate the power of the lens.
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 ______.
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 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?
The lens of power + 1·0 D is ______.
In what unit is the power of a lens expressed?
