Cheat Sheet — NEET Ray Optics Quick Reference (Pinned) — Notes

MASTER CHEAT SHEET — RAY OPTICS OP-01

Sign Convention (NEVER FORGET)

u = ALWAYS NEGATIVE (object always on left)
Concave mirror: f < 0 | Convex mirror: f > 0
Convex lens: f > 0 | Concave lens: f < 0
Mirror real image: v < 0 | Mirror virtual: v > 0
Lens real image: v > 0 | Lens virtual: v < 0

Core Formulas

Formula	Mirror	Lens
Distance formula	1/v + 1/u = 1/f	1/v − 1/u = 1/f
Magnification	m = −v/u	m = v/u
Focal-radius	f = R/2	—
Power	—	P = 1/f (D)

Critical Differences (NEET TRAPS)

Mirror: + between terms. Lens: − between terms.
Mirror m has − sign. Lens m has NO minus.
Concave mirror: f NEGATIVE. Convex lens: f POSITIVE.

TIR

$\sin\theta_c = \frac{n_2}{n_1} \quad (n_1 > n_2)$ Both conditions: (1) Denser → Rarer. (2) θ > θ_c.

Prism

$\delta = (i+e) - A \quad ; \quad n = \frac{\sin\!\left(\frac{A+\delta_m}{2}\right)}{\sin\!\left(\frac{A}{2}\right)}$ Thin prism (A < 10°): δ = (n−1)A only.

Lensmaker's Equation

$\frac{1}{f} = (n-1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$ Biconvex equal R: 1/f = 2(n−1)/R.

Optical Instruments

Instrument	M	L
Simple magnifier	1 + D/f (at D)	—
Compound microscope	−(L/f_o)(D/f_e)	L + f_e
Astronomical telescope	−f_o/f_e	f_o + f_e

MICROSCOPE: objective SHORT f. TELESCOPE: objective LONG f.

Image Nature Quick Table

Setup	Nature	m sign
Concave mirror, obj beyond F	Real, inverted	m < 0
Concave mirror, obj between F and P	Virtual, erect, magnified	m > 0, \|m\| > 1
Convex mirror, any position	Virtual, erect, diminished	0 < m < 1
Convex lens, obj beyond F	Real, inverted	m < 0
Convex lens, obj inside F	Virtual, erect, magnified	m > 0, \|m\| > 1
Concave lens, any position	Virtual, erect, diminished	0 < m < 1

Diamond TIR

n = 2.42 → θ_c = 24.4° (very small → brilliant sparkle)

NoteTube

Cheat Sheet — NEET Ray Optics Quick Reference (Pinned)