Advertisements
Advertisements
प्रश्न
A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?
Advertisements
उत्तर
Power of a lens is given by:
Power (P) `=1/f``
`f=-10` cm
∴` p=1/(10xx10^2)=-10 D`
Negative sign indicates it is a diverging lens.
APPEARS IN
संबंधित प्रश्न
State power of a lens S.I. unit.
(a) At what distance should the lens be held from the figure in order to view the squares distinctly with the maximum possible magnifying power?
(b) What is the magnification in this case?
(c) Is the magnification equal to the magnifying power in this case? Explain.
You have two lenses A and B of focal lengths +10 cm and –10 cm, respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens? Draw a ray diagram to justify your answer
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.
The focal length of a convex lens is 25 cm. What is its power?
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?
A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with one another.
(a) What is the power of this combination?
(b) What is the focal length of this combination?
(c) Is this combination converging or diverging?
The power of a lens is +2.0D. Its focal length should be :
How does the power of a lens change if its focal length is doubled?
How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for your answer.
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 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?
Surabhi from std. X uses spectacle. The power of the lenses in her spectacle is 0.5 D.
Answer the following questions from the given information:
- Identify the type of lenses used in her spectacle.
- Identify the defect of vision Surabhi is suffering from.
- Find the focal length of the lenses used in her spectacle.
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.
A stick partly immersed in water appears to be bent. Draw a ray diagram to show the bending of the stick when placed in water and viewed obliquely from above.
If focal length of a convex lens is 20 cm at what is the power of the lens?
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.
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?
