Power Of A Lens — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Power of a Lens Applicable in Ray Optics for thin spherical lenses. The power of a lens is defined as the tangent of the angle by which it converges or diverges a beam of light falling at unit distant from the optical center. For small angles (paraxial approximation), tan(δ) ≈ δ. From geometry, δ = h/f. If h=1, then P = 1/f. Focal length 'f' must be in meters to obtain Power 'P' in Diopters. Assumes the lens behaves as a thin lens. Valid for paraxial rays. Plugging in focal length in centimeters (cm) instead of meters (m). For cm, the formula is P = 100/f(cm). Ignoring the sign convention: Convex lens f is +ve (P is +ve), Concave lens f is -ve (P is -ve). Confusing optical power with magnification power.