Optics Formula Sheet for NEET

Reflection & Mirrors

• Mirror formula: $1/v + 1/u = 1/f$; $m = -v/u$.
• Concave mirror: $f<0$, real image for $u<2f$.

Refraction

• Snell: $n_1 \sin i = n_2 \sin r$; $n = c/v = \lambda_{vac}/\lambda_{med}$.
• Critical angle: $\sin\theta_c = 1/n$.
• Apparent depth = actual/n; shift = t(1−1/n).

Lenses

• $1/v - 1/u = 1/f$; $P = 1/f$ (in m).
• Lensmaker: $1/f = (n-1)(1/R_1 - 1/R_2)$.
• Combination in contact: $P = P_1 + P_2$.
• Magnifying power (compound microscope): $M = -(L/f_o)(D/f_e)$; simple microscope $= 1 + D/f$.

Prism

• $A + \delta = i + e$; at minimum deviation: $i=e$, $r_1=r_2=A/2$.
• $n = \sin((A+\delta_m)/2)/\sin(A/2)$.
• Angular dispersion $\delta_v-\delta_r$; dispersive power $\omega = (\delta_v-\delta_r)/\delta_y$.

Human Eye

• Least distance of distinct vision = 25 cm.
• Myopia: concave lens; Hypermetropia: convex; Presbyopia: bifocal.

Wave Optics (NEET portion)

• YDSE fringe width $\beta = \lambda D/d$.
• Constructive: $\Delta x = n\lambda$; destructive: $(n+1/2)\lambda$.
• Single slit angular width of central max = $2\lambda/a$.
• Polarisation: Brewster $\tan i_p = n$; Malus $I = I_0\cos^2\theta$.

Optical Instruments (Numerical Tricks)

• Simple microscope max magnification: $1 + D/f$.
• Astronomical telescope: $M = -f_o/f_e$; $L = f_o + f_e$ (normal adjustment).
• Angular resolution of eye ~ 1 minute of arc = 3×10⁻⁴ rad.

Practice MCQs

Q1. Refractive index of a medium in which light travels at 2×10⁸ m/s is A) 1.5 B) 1.33 C) 1.0 D) 2.0

Q2. A converging lens of f=20 cm forms an image at 30 cm. Object distance is A) −60 B) −30 C) −15 D) −12

Q3. Least distance of distinct vision for normal eye is A) 25 mm B) 25 cm C) 250 mm D) 1 m

Q4. Fringe width in YDSE with d=1 mm, D=1 m, λ=600 nm is A) 0.3 mm B) 0.6 mm C) 1.2 mm D) 6 mm

Q5. Prism angle 6°, n=1.5, min deviation is A) 1° B) 2° C) 3° D) 4°

Q6. Astronomical telescope magnifying power at normal adjustment with fo=100 cm, fe=5 cm is A) 10 B) 15 C) 20 D) 25

Q7. A ray at 45° enters glass of n=√2. Refracted ray angle is A) 15° B) 30° C) 45° D) 60°

Q8. Myopia is corrected by A) Convex B) Concave C) Cylindrical D) Bifocal

Q9. A convex lens acts as diverging lens when placed in a medium of A) Lower n B) Higher n C) Equal n D) Water

Q10. Brewster's angle for glass (n=1.5) is A) 30° B) 45° C) 56.3° D) 60°

Answers: 1-A (c/v = 3×10⁸/2×10⁸ = 1.5.), 2-A (1/30 − 1/u = 1/20.), 3-B (25 cm standard.), 4-B (β=600×10⁻⁹×1/10⁻³=6×10⁻⁴ m=0.6 mm.), 5-C (δ=(n−1)A=3°.), 6-C (fo/fe=20.), 7-B (sin 45°/sin r = √2 → sin r = 0.5 → 30°.), 8-B (Diverging lens.), 9-B (If surrounding n > lens n, focal length changes sign.), 10-C (tan⁻¹(1.5) ≈ 56.3°.)

MCQ Metadata