Overview — 10-Sentence Concise Summary — Summary

Ray optics treats light as straight rays, governed by reflection (angle in = angle out) and refraction (Snell's law: n_{1} sin θ_{1} = n_{2} sin θ_{2}).
In the Cartesian sign convention, the object distance u is always negative (object on the left), and distances are measured from the pole or optical center.
The mirror formula 1/v + 1/u = 1/f uses a plus sign; the thin lens formula 1/v − 1/u = 1/f uses a minus sign — confusing these is the most common NEET error.
Mirror magnification is m = −v/u (with a minus sign); lens magnification is m = v/u (no minus sign).
Concave mirrors and convex lenses converge light; convex mirrors and concave lenses diverge it.
Total internal reflection occurs only when light travels from a denser to a rarer medium AND the angle exceeds the critical angle θ_c = arcsin(n_{2}/n_{1}).
A prism deviates light toward its base; minimum deviation occurs when i = e, giving n = sin((A + δ_m)/2)/sin(A/2).
Power P = 1/f (in dioptres), and thin lenses in contact have combined power P = $P_{1}$ + $P_{2}$ .
A compound microscope uses an objective with short focal length; an astronomical telescope uses an objective with long focal length — knowing which is which is essential for NEET.
NEET consistently tests 3–4 questions from ray optics, primarily on sign convention calculations, TIR conditions, prism minimum deviation, lens power, and optical instrument magnification.