Mirror Formula — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Mirror Formula Determines the relationship between object distance, image distance, and focal length for spherical mirrors under paraxial ray conditions. Draw a ray diagram for a spherical mirror (concave or convex) Use similar triangles formed by the object, image, and the center of curvature or pole Establish ratios of heights to distances from the pole Apply the paraxial approximation for small angles Substitute geometric distances with algebraic symbols using sign convention Mirror must be spherical Rays must be paraxial (near the principal axis) Sign convention (e.g., Cartesian) must be applied consistently Applying the formula to lenses where the sign is actually negative (1/f = 1/v - 1/u) Forgetting to use negative signs for real object distances (u is usually negative) Assuming the formula is accurate for wide-aperture mirrors where spherical aberration occurs