The Total solution for NCERT class 6-12
Ascreen is placed 90 cm from an object. The image of the object on the screen isformed by a convex lens at two different locations separated by 20 cm.Determine the focal length of the lens.
Distance between the image (screen) and theobject, D = 90 cm
Distance between two locations of the convexlens, d = 20 cm
Focal length of the lens = f
Focal length is related to d and D as:
Therefore,the focal length of the convex lens is 21.39 cm.