Advertisements
Advertisements
प्रश्न
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.
Advertisements
उत्तर
Since the image is real and same size. The position of image should be at 2F.
It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of 50 cm.
Object distance, u = – 50 cm
Image distance, v = 50 cm
Focal length = f
According to the lens formula,
`1/v-1/u = 1/f`
`1/f = 1/50 - 1/(-50)`
`=1/50 + 1/50 = 1/25`
f = 25 cm
Power of lens, `p = 100/f ("cm")D`
= `100/25D`
= 4D
APPEARS IN
संबंधित प्रश्न
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
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
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
Which one of the following materials cannot be used to make a lens?
The focal length of a convex lens is 25 cm. What is its power?
A converging lens has focal length of 50 mm. What is the power of the lens?
A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?
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 is the unit of power of a lens? Define the unit of power of a 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.
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
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.
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.
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?
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.
Focal length : metre : : power of 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 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?
