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The power of a lens is -2.5 D. Its focal length is

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Important Questions on Refraction through Lens

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Science>Physics>Refraction through Lens>Power of a Lens
A man used a convex lens of focal length of 20 cm in his specs, the power of this lens is:
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Science>Physics>Refraction through Lens>Power of a Lens
The power of a plane mirror is :
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Science>Physics>Refraction through Lens>Power of a Lens
The unit of power of a lens is dioptre. Then 1 dioptre is equal to :
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Science>Physics>Refraction through Lens>Power of a Lens
Focal length of a lens is 50 cm. In dioptre power of lens will be.
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Science>Physics>Refraction through Lens>Power of a Lens
Find the power of a concave lens of focal length 2 m?
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Science>Physics>Refraction through Lens>Power of a Lens
Two thin lenses of focal length f1and f2 are in contact and coaxial. Its power is the same as the power of a single lens given by
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Science>Physics>Refraction through Lens>Power of a Lens
If F be the focal length of a convex lens, then the nature of image of an object placed at a distance 2F will be :
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Science>Physics>Refraction through Lens>Power of a Lens
An object of height 4.0 cm is placed at a distance of 30 cm from the optical centre ‘O’ of a convex lens of focal length 20 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’ and principal focus ‘F’ on the diagram. Also, find the approximate ratio of the size of the image to the size of the object.
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Science>Physics>Refraction through Lens>Power of a Lens

A person can not clearly see objects at a distance more than 40 cm. He is advised to use lens of power

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Science>Physics>Refraction through Lens>Power of a Lens
The focal length of a convex lens is 20 cm. Its power is :
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Science>Physics>Refraction through Lens>Power of a Lens
A concave lens has focal length 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens.
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Science>Physics>Refraction through Lens>Power of a Lens

Which of the following statements is true?

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Science>Physics>Refraction through Lens>Power of a Lens
Define power of a lens. What is its unit?
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Science>Physics>Refraction through Lens>Power of a Lens
The focal length of a convex lens is 20 cm. The images formed is double the length of the object. The distance of the object from the lens is
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Science>Physics>Refraction through Lens>Power of a Lens

An object is placed at a distance 24 cm in front of a convex lens of focal length 8 cm.
(i) Calculate the distance of the image from the lens.
(ii) Calculate the magnification of the image.

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Science>Physics>Refraction through Lens>Power of a Lens
What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length 40 cm and another of -20 cm. Write the nature and power of each lens. 
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Science>Physics>Refraction through Lens>Power of a Lens
A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 18 cm. Find the nature, position and size of the image formed.
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Science>Physics>Refraction through Lens>Power of a Lens
Select the correct statement.
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Science>Physics>Refraction through Lens>Power of a Lens
A person needs a lens of power -4.5 D for correction of his/her vision, then the focal length of corrective lens is.
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Science>Physics>Refraction through Lens>Power of a Lens
The central point of a lens is known as: