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JEE Main202125 Feb 2021Morning ShiftPhysicsRay OpticsActual

The same size images are formed by a convex lens when the object is placed at 20   cm or at 10   cm from the lens. The focal length of convex lens is

Correct answer

15

Step-by-step solution

m = f u + f + m = f - 10 + f         . . . . 1 - m = f - 20 + f           . . . . . 2 1 / 2 - 1 = f - 20 f - 10 10 - f = f - 20 30 = 2 f f = 15   cm

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