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प्रश्न
How is the power of a lens related to its focal length?
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उत्तर
The power of a lens is related to the focal length as:
Power (P)=`I/f'`
where, f is measured in metres and P in dioptres.
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संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2D.
Define the power of a lens.
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
The power of a lens is + 0.2 D. Calculate its focal length.
The focal length of a lens is +150 mm. What kind of lens is it and what is its power?
The power of a combination of two lenses X and Y is 5 D. If the focal length of lens X be 15 cm :
(a) calculate the focal length of lens Y.
(b) state the nature of lens Y.
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?
The power of a lens is + 1.0 D is :
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 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.
The following diagram shows the object O and the image I formed by a lens. Copy the diagram and on it mark the positions of the lens LL’ and focus (F). Name the lens.
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.
A convex lens is of focal length 20 cm. Find its power.
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.
Power of a lens is – 4D, then its focal length is
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.
In what unit is the power of a lens expressed?
