Qstnid -20- A Screen Is Placed 90 Cm From An Object. The Image Of The Object On The Screen Is Formed By A Convex Lens At Two Different Locations Separated By 20 Cm. Determine The Focal Length Of The Lens. - 09: Ray Optics And Optical Instruments - Neet-xii-physics

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NEET-XII-Physics

09: Ray Optics And Optical Instruments

II - page 3

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#20
A screen is placed 90 cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20 cm. Determine the focal length of the lens.

Ans : Distance between the image (screen) and the object, D = 90 cm

Distance between two locations of the convex lens, 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.