Focal Length Of A Convex Lens By U V Method — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Focal length of a Convex Lens by u-v method Used in optical bench experiments to determine the focal length of a converging lens by locating the real image of an object needle. Start with the Gaussian lens formula: 1/v - 1/u = 1/f Apply sign convention for a real object and real image: u is negative (-u), v is positive (+v) Substitute: 1/v - 1/(-u) = 1/f implies 1/v + 1/u = 1/f Solve for f: f = (u v) / (u + v) Applicable for real images only Object must be placed beyond the focus (u > f) Assumes a thin lens Parallax between the image needle and the real image must be removed Confusing u and v as coordinates rather than distances in this specific rearranged formula Forgetting to remove parallax properly before taking readings Assuming f is negative (convex lenses always have positive focal length)