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Class X Sciences [papers from previous years] To determine focal length of a concave mirror a student obtains the image of a well lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between: (A) mirror and the object (B) mirror and the screen (C) screen and the object (D) screen and the object and also mirror and the screen

Answer»

tance between the pole of the mirror and the image of a distant object is called the focal length of the concave mirror.1/f = 1/ u + 1/V        for a mirror.If the object is distant,    u >> f  or  u >> v.    so  1/u  <<  1/v  or  1/f.so we IGNORE it.  1/f = 1/v    =>    f = v.v is the distance between the mirror and the screen.u = distance between the mirror and the object.f = focal length of the mirror.



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