Question

write down the steps to determine the f of a given convex lens by obtaining a sharp image of a distant object

Answer 1

after getting the sharp image in screen , measure the perpendicular distance between lens and screen which is focal length.

hope this helps you./....:-)

Answer 2

Take a plank or a sheet of paper with the lens right in front of it.
try to obtain the smallest dot formed by light rays of any luminous or non-lumunious object.
The next step is to measure the distance perpendicularly.
Hence, you obtain the focal length(f)
remember that focal length is half of the radius of curvature..i.e.
2f=R