Q11 of 45 Page 302

A needle placed at 30 cm from the lens forms an image on a screen placed 60 cm on the other side of the lens. Identify the type of lens and determine the focallength.

As the image is formed on the other side of the lens so the lens is a converging lens or convex lens.

Given,


Object length (u) =-30cm


Image length (v) =+60cm


Focal length (f) =?


According to the lens formula,








Hence, the focal length of the convex lens is 20cm


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