Advertisements
Advertisements
प्रश्न
Find the focal length of a lens of power −2.0 D. What type of lens is this?
उत्तर
Power of lens,
P = −2.0 D
P = `1/"f"`
∴ f = `1/"P"`
= `1/(-2.0 "D")`
= −0.5 m
A concave lens has a negative focal length. Hence, it is a concave lens.
APPEARS IN
संबंधित प्रश्न
State power of a lens S.I. unit.
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
Ranbir claims to have obtained an image twice the size of the object with a concave lens. Is he correct? Give a reason for your answer.
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
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.
A diverging lens has focal length of 3 cm. Calculate the power.
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 lens has both its focal lengths equal .
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.
What is meant by the power of accommodation produced?
Which lens has more power a thick lens or a thin lens?
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.
Complete the diagram to show the formation of the image of the object AB.
(i) Name the Lens LL’.
(ii) Where is the image of the object AB formed?
(iii) State three characteristics of the image.
If there is a convex lens of focal length 75 cm and a concave lens of focal length 40 cm, then calculate their combined power and combined focal length.
The power of the magnifying glass depends on the distance of the magnifying glass from object.
What is power of accommodation of eye?
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.
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.
