Magnification Mirror — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Magnification (Mirror) Applicable to spherical mirrors (concave and convex) under the paraxial ray approximation. Define magnification m as the ratio of image height (h') to object height (h). Use similar triangles formed by the object, image, and the pole (P) of the mirror to show m = -v/u. Rearrange the mirror formula (1/v + 1/u = 1/f) to express v in terms of f and u: v = (u f)/(u-f). Substitute this expression of v into m = -v/u to derive m = f/(f-u). The object must be perpendicular to the principal axis. Valid only for paraxial rays (rays making small angles with the principal axis). Sign convention (usually Cartesian) must be applied consistently to u, v, and f. Confusing mirror magnification (m = -v/u) with lens magnification (m = +v/u). Forgetting that a positive m indicates a virtual and erect image, while a negative m indicates a real and inverted image. Applying the formula without considering the sign convention for f (negative for concave, positive for convex).