Question:
A screen is placed 90cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20cm. Determine the focal length of the lens.
Answer:
Distance between the object and the image (D) = 90 m
Distance between two location of the convex lens (d) = 20 m
Focal length of the lens (f) = D2 - d2/ 4D
= (90)2 - (20)2/4x90
= 770/36 = 21.93 cm
Hence, the Focal length of the lens is 21.93 cm.
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