Lens Maker S Formula — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Lens Maker's Formula Valid for thin lenses where the thickness is negligible compared to the radii of curvature. Assumes paraxial rays and a homogeneous surrounding medium. Apply the refraction formula at a single spherical surface for the first interface (air to lens). Treat the image formed by the first surface as the virtual object for the second interface (lens to air). Apply the refraction formula for the second interface. Add the two equations and neglect lens thickness to relate object and final image distances to R1, R2, and refractive index. Substitute object distance = infinity and image distance = f to obtain the final formula. Lens must be thin Rays must be paraxial (small angles) Surrounding medium on both sides must be the same Ignoring the sign convention for R1 and R2 (e.g., assuming R is always positive). Using the absolute refractive index of the lens instead of the relative refractive index (lens w.r.t surrounding) when the lens is submerged in a liquid. Assuming R1 always corresponds to the left surface physically, rather than the surface light hits first.