Advertisements
Advertisements
प्रश्न
A combination of lenses for a camera contains two converging lenses of focal lengths 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.
Advertisements
उत्तर
Focal length (f1) of the 1st converging lens = 20 cm = 0.2 m
Focal length (f2) of the 2nd converging lens = 40 cm = 0.4 m
Focal length (f3) of the diverging lens = −50 cm = −0.5 m (negative sign due to sign convention)
Power = `1/"Focal length of lens (in metre)"`
Power (P1) of 1st lens = `1/0.2` = 5 D
Power (P2) of 2nd lens = `1/0.4` = 2.5 D
Power (P3) of diverging lens = `1/0.5` = −2 D
Net power of the combination = P1 + P2 + P3
= 5 + 2.5 + (−2)
= 7.5 − 2
= 5.5 D
Net focal length of the combination = `1/"Net power"`
= `1/5.5`
= 0.1818 m
= 18.18 cm
संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2D.
What is meant by a power of a lens? Define its SI unit.
Which type of lens has a positive power?
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, −2 D. What is its focal length?
What is the nature of a lens whose power is, −4 D?
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 ___________.
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.
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?
A diverging lens has a focal length of 0.10 m. The power of this lens will be:
State the condition for the following a ray passes undeviated through the lens .
Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:
(1) a blurred image on the wall of the laboratory.
(2) an erect image of the tree on the lens.
(3) no image as the screen has been removed
(4) an inverted image of the tree at the focus of the lens.
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 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?
The power of the magnifying glass depends on the distance of the magnifying glass from object.
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?
The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is ______ cm.
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.
One dioptre is the power of a lens whose focal length is:
The power of a lens placed in a medium is given by:
A negative power of a lens indicates a:
A greater numerical value of the power of a lens means:
A convex lens has:
A concave lens has:
The power of a lens of focal length \[f = 0.5\,m\] is:
