Optics Formula & Concept Cheat Sheet - NEET 2027

1. Reflection & Geometrical Optics

Geometrical optics deals with the reflection and refraction of light ray beams assuming rectilinear propagation. In spherical mirrors, ray tracing follows strict Cartesian sign conventions.

Key Formulas

• Law of Reflection: \(\theta_i = \theta_r\)
• Focal Length of Spherical Mirror: \(f = \frac{R}{2}\)
• Mirror Formula: \[\frac{1}{f} = \frac{1}{v} + \frac{1}{u}\]
• Linear Magnification: \[m = \frac{h_i}{h_o} = -\frac{v}{u} = \frac{f}{f-u}\]

2. Refraction & Snell's Law

Refraction occurs when light passes from one medium to another, causing a change in velocity and wavelength while frequency remains invariant.

Key Formulas & Concepts

• Snell's Law: \(n_1 \sin\theta_1 = n_2 \sin\theta_2\)
• Refractive Index: \(n = \frac{c}{v} = \frac{\lambda_0}{\lambda}\)
• Apparent Depth (Observer in Rarer Medium): \[d' = \frac{d}{n}\]
• Apparent Shift: \[\Delta d = d\bigl(1 - \frac{1}{n}\bigr)\]
• Critical Angle for Total Internal Reflection (TIR): \[\sin\theta_c = \frac{n_2}{n_1} \quad (n_1 > n_2)\]

3. Prism Optics

A prism bends ray beams toward its base. Deviations depend on the angle of incidence, prism angle, and refractive index.

Key Formulas

• Angle of Prism: \(A = r_1 + r_2\)
• Angle of Deviation: \(\delta = i + e - A\)
• Refractive Index at Minimum Deviation (\(\delta_m\)): \[n = \frac{\sin\bigl(\frac{A + \delta_m}{2}\bigr)}{\sin\bigl(\frac{A}{2}\bigr)}\]
• Small-Angle Prism Deviation: \(\delta \approx (n - 1)A\)

4. Thin Lenses & Lens Combinations

Lenses use refraction across spherical surfaces to converge or diverge light rays.

Key Formulas

• Lens Maker's Formula: \[\frac{1}{f} = \bigl(\frac{n_l}{n_m} - 1\bigr)\bigl(\frac{1}{R_1} - \frac{1}{R_2}\bigr)\]
• Thin Lens Formula: \[\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\]
• Magnification: \[m = \frac{h_i}{h_o} = \frac{v}{u} = \frac{f}{f+u}\]
• Power of a Lens: \(P = \frac{1}{f \text{ (in m)}}\) (in Diopters, D)
• Combination of Lenses in Contact: \[\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2} \implies P = P_1 + P_2\]

5. NEET PYQ Analysis & Chapter Weightage

NTA Pattern Trends: Optics is one of the highest-weightage units in NEET Physics, consistently accounting for 4 to 5 questions (16-20 marks) in the exam.

• High-Yield Topics: Total Internal Reflection applications (optical fibers), Lens Maker's Formula, Combination of Lenses, and Minimum Deviation in Prisms.
• PYQ Focus: Most numerical questions evaluate correct sign convention application in Lens Maker's Formula and apparent depth shift calculations.

6. People Also Ask (FAQ)