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Material: Convex lens, screen, metre scale, stand for the lens etc.
Method:
Keeping the screen fixed, obtain a clear image of a distant object like a tree or a building with the help of the lens on the screen. Measure the distance between the screen and the lens with the help of the metre scale. Now tum the other side of the lens towards the screen. Again obtain a clear image of the distant object on the screen by moving the lens forward or backward. Measure the distance between the screen and the lens again.
Discuss the relation between this distance and the radius of curvature of the lens with your teacher.

Explanation

The focal length and radius of curvature of the lens are related with each other by lens maker's equation given by,
`(1)/(f)=(n-1)((1)/(R_(1))-(1)/(R_(2)))`
Where,
n = Refractive index of material of lens,
`R_(1) and R_(2)` = Radii of curvature of two surfaces of the lens.