Linear Magnification Lenses — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Linear Magnification (Lenses) Applies to thin spherical lenses (convex and concave) under the paraxial approximation. Consider a ray starting from the top of the object and passing through the optical center of the lens. This ray passes undeviated. Two similar triangles are formed: one by the object and the principal axis, and one by the image and the principal axis. The ratio of the perpendicular sides (heights) equals the ratio of the base sides (distances). Using sign convention, h i/h o = v/u. Cartesian sign convention must be strictly followed. Distances are measured from the optical center. Heights are measured from the principal axis (upward positive, downward negative). Confusing the lens magnification formula (v/u) with the mirror magnification formula (-v/u). Assuming magnification 'm' is always positive; negative m indicates a real, inverted image. Believing that m < 1 implies the image is virtual (magnitude < 1 simply means diminished). Forgetting to apply sign conventions to given values of u and v before calculating.