Advertisements
Advertisements
प्रश्न
The focal length of a convex lens is 25 cm. What is its power?
Advertisements
उत्तर
Given, f = 25 cm
Power of a lens is given by:
Power (p)=1/f
`p=1/(25xx10^-2)=100/25=4.D`
APPEARS IN
संबंधित प्रश्न
Define the power of a lens.
A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
Name the physical quantity whose unit is dioptre.
Which type of lens has (a) a positive power, and (b) a negative power?
A diverging lens has focal length of 3 cm. Calculate the power.
A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?
An object of height 4.25 mm is placed at a distance of 10 cm from a convex lens of power +5D. Find (i) the focal length of the lens, and (ii) the size of the image.
What do you understand by the power of a lens? Name one factor on which the power of a lens depends.
Express the power (with sign) of a concave lens of focal length 20 cm.
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.
A double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double of the other. Find the radii, if the refractive index of the material of the lens is 1.5.
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 |
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.
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.
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?
In what unit is the power of a lens expressed?
