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Ashok0210
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Asked: 2021-03-21T03:50:23+00:00 In:

The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?

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Class 12 Physics
CBSE and UP Board
Ray Optics and Optical Instruments
Chapter-9 Exercise 9.19
NCERT Solutions for Class 12 Physics Chapter 9 Question-19

2020-2021cbse and up boardclass 12 chapter-9 physicsclass 12 physicsncert class 12 ray optics and optical instruments
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    1. Best Answer

      Distance between the object and the image, d = 3 m

      Maximum focal length of the convex lens = fmax

      For real images, the maximum focal length is given as:

       fmax  =  d/4 =3/4 =0.75 m

      Hence, for the required purpose, the maximum possible focal length of the convex lens is 0.75 m.

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