Question

Collect information about lenses available in an optical shop find out how the focal length of lens may be determined by the given power of lens

Answer 1

 principal focal length of a lens is determined by the index of refraction of the glass, the radii of curvature of the surfaces, and the medium in which the lens resides. It can be calculated from the lens-maker's formula for thin lenses.

Answer 2

If you know the focal length & just apply P = 1/f , you will get focal length , f = 1/P