Law of Reflection: Angle of incidence = angle of reflection (from normal). Plane mirror image: virtual, erect, laterally inverted, same size, same distance behind mirror.

Spherical Mirror Formula: 1/v + 1/u = 1/f. All distances from pole P. u is always negative. Concave: f < 0. Convex: f > 0. f = R/2. Mirror magnification: m = −v/u (negative sign mandatory).

Cartesian Sign Convention: Right = positive, Left = negative. Heights above axis = positive. Object is always left → u always negative. This is the foundation of all NEET ray optics calculations.

Snell's Law: n_{1} sin θ_{1} = n_{2} sin θ_{2}. Light bends toward normal entering denser medium. Refractive index n = c/v ≥ 1, dimensionless.

Total Internal Reflection: Needs (1) denser → rarer medium AND (2) angle > θ_c = arcsin(n_{2}/n_{1}). Applications: optical fibres, diamond sparkle (n=2.42, θ_c=24.4°), mirage, reflecting prisms.

Thin Lens Formula: 1/v − 1/u = 1/f (MINUS between terms, not plus). u < 0. Convex lens: f > 0. Concave: f < 0. Lens magnification: m = v/u (NO minus sign — unlike mirrors).

Power of Lens: P = 1/f (f in metres). Unit: dioptre (D). Convex: P > 0. Concave: P < 0. Combination in contact: P = $P_{1}$ + $P_{2}$.

Lensmaker's Equation: 1/f = (n−1)(1/$R_{1}$ − 1/$R_{2}$). For biconvex equal radii: 1/f = 2(n−1)/R. Biconvex: $R_{1}$ > 0, $R_{2}$ < 0.

Prism: δ = (i+e) − A. Minimum deviation: i = e, r = A/2. n = sin((A+δ_m)/2)/sin(A/2). Thin prism (A < 10°) only: δ = (n−1)A.

Dispersive Power: ω = (n_v − n_r)/(n_y − 1). Material property, independent of prism angle A.

Simple Magnifier: M = 1 + D/f (at D), D/f (at ∞). D = 25 cm.

Compound Microscope: Objective has SHORT f. M = −(L/f_o)(D/f_e) at ∞. L = tube length.

Astronomical Telescope: Objective has LONG f. M = −f_o/f_e (normal adjustment). L = f_o + f_e. Image: inverted, virtual.

NEET Top Traps: (a) Using f = +ve for concave mirror. (b) Using m = −v/u for a lens. (c) Using thin prism formula for A = 60°. (d) Claiming TIR from rarer to denser medium.

Real vs Virtual (Mirror/Lens): Mirror: v < 0 = real. Lens: v > 0 = real. These are OPPOSITE conventions.