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
What is meant by a power of a lens? Define its SI unit.
Define 1 dioptre of power of a lens.
The lens mentioned in 6(b) above is of focal length 25cm. Calculate the power of the 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
Consider two statements A and B given below:
A: real image is always inverted
B: virtual image is always erect
Out of these two statements:
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power: A or B.
Name the physical quantity whose unit is dioptre.
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?
What is the nature of a lens having a power of + 0.5 D?
What is the nature of a lens whose power is, −4 D?
A doctor has prescribed a corrective lens of power, −1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
What is the unit of power of a lens? Define the unit of power of a lens.
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 :
Define the term focal length of a lens.
State the condition for the following a lens has both its focal lengths equal .
State the condition for the following a ray passes undeviated through the lens .
Find the radius of curvature of the convex surface of a plano-convex lens, whose focal length is 0.3 m and the refractive index of the material of the lens is 1.5.
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
A pin of length 2.00 cm is placed perpendicular to the principal axis of a converging lens. An inverted image of size 1.00 cm is formed at a distance of 40.0 cm from the pin. Find the focal length of the lens and its distance from the pin.
A convex lens produces a double size real image when an object is placed at a distance of 18 cm from it. Where should the object be placed to produce a triple size real image?
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.
Focal length : metre : : power of lens : _______
Power of a lens is – 4D, then its focal length is
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.
The focal length of a concave lens is 20 cm. The focal length of a convex lens is 25 cm. These two are placed in contact with each other. What is the power of the combination? Is it diverging, converging or undeviating in nature?
When monochromatic red light is used instead of blue light in a convex lens, its focal length will ______.
The power of convex lens of focal length 20 cm is ______.
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 power of a lens is defined as the:
A positive power of a lens indicates a:
A negative power of a lens indicates a:
A greater numerical value of the power of a lens means:
If the refractive index of the lens material is less than that of the surrounding liquid (\[n_2 < n_1\]), then:
A concave lens has:
A lens has a power of \[+2\,D\]. Its focal length is:
