A lens forms a real image of an object. The distance from the object to the lens is u cm and distance of the image from the lens is v cm. The given graphs shows variation of v with 
(i) What is the nature of the lens?
(ii) Using the graph, find the focal length of this lens.

Dear Student ,
From the graph, when u=20 cm , we have v = 20 cm. For the convex lens forming a real iamge, u is negative and v and f are positive. u= -20 cm  and v = +20cm Using this lens formula, 1f = 1v  1u = 120  1-20= 110f =+10 cm


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10 cm and convex lens
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