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When a convex lens forms an image whose size is equal to that of the object, the object is placed

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Important Questions on Light

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The following diagram shows the use of an optical device to perform an experiment of light.

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As per the arrangement shown, the optical device is likely to be a _____.

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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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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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A converging lens forms a three times magnified image of an object, which can be taken on a screen. If the focal length of the lens is 30 cm, then the distance of the object from the lens is _____.

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If the lens is placed in water instead of air, how does its focal length change? 
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If a lens can converge the sun rays at a point 20 cm away from its optical centre, the power of this lens is _____.

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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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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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An object is placed at a distance 24 cm in front of a convex lens of focal length 8 cm. What is the nature of the image so formed?
HARD

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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The central point of a lens is known as:
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Define power of a lens. What is its unit?
HARD

Which of the following statements is true?

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A student wants to obtain magnified image of an object AB as on a screen. Which one of the following arrangements shows the correct position of AB for him/her to be successful?

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

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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Find the power of a concave lens of focal length 2 m?
HARD

A virtual, diminished image is formed when an object is placed between the optical centre and the principal focus of a lens.
(i) Name the type of lens which forms the above image.
(ii) Draw a ray diagram to show the formation of the image with the above stated characteristics.  

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Which lens, thick or thin has greater focal length?
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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.