Sign in

Playbook

Light and Optics

97 q · 10% HARD — the largest chapter. Hybrid: half recall (Light Phenomena, Optical Instruments, Eye defects), half formula-apply (mirror formula, lens formula, Snell's law, lens-power calc). Drill Light Phenomena + Optical Instruments first for fast marks.

questions in the bank
97
tagged HARD
10%
subtopic(s)
6
worked examples
2

When you’ll see it

A mirror/lens formula calculation, a Snell's-law refraction, a TIR critical-angle, a prism-deviation, an eye-defect correction, or a 'which colour bends most' dispersion question.

How this chapter is tested

97 q in 10 years — NDA Physics's largest chapter. Half RECALL (Light Phenomena, Optical Instruments, Eye defects — 42 q), half FORMULA-APPLY (Reflection, Refraction, Lenses, Prisms — 55 q). Drill recall subtopics fast for guaranteed marks; train the formula sign convention separately for the calculation subtopics.

The mirror formula 1/v + 1/u = 1/f and lens formula 1/v − 1/u = 1/f are nearly identical — the lens has a minus where the mirror has a plus. Magnification = v/u (lens) or −v/u (mirror). Cartesian sign convention: distances measured from pole, +x to the right. Real object always has u < 0. f is negative for diverging optics (concave lens, convex mirror).

Snell's law μ = sin i / sin r is the second pillar. n = c/v in medium. TIR happens only DENSE→RARE when i > critical angle (sin θ_c = 1/μ). Light Phenomena tests the qualitative shape: violet bends MOST, red bends LEAST (high-frequency = higher refractive index in normal media). Sky is blue because of Rayleigh scattering (λ⁻⁴, short wavelengths scatter more).

The sub-skills

The rules and habits that decide whether you get a question right.

  • Cartesian sign convention discipline

    Distances from pole, +x to the right (direction of incident light). Real object: u negative. Real image on same side as outgoing light: v positive (lens) or negative (mirror — convention varies, check). Always draw the ray first.

  • Mirror/lens formula application

    Identify f sign (concave mirror/convex lens: +; convex mirror/concave lens: −). Plug u with sign. Solve for v. Magnification m = v/u (lens) or −v/u (mirror).

  • Snell's law + TIR check

    μ_1 sin θ_1 = μ_2 sin θ_2. Going dense→rare, check whether θ_1 exceeds critical angle (sin θ_c = μ_rare/μ_dense). Above θ_c, TIR (no refraction).

  • Light phenomena recall (Phenomena + Instruments)

    Sky blue = Rayleigh scattering (λ⁻⁴). Red sunset = scattering of short wavelengths leaving long ones. Rainbow = refraction + TIR + dispersion in water drops. Mirage = continuous refraction in hot-air layers.

2 worked examples from the bank

Real past-year questions illustrating the playbook. Click to reveal options + solution.

Example 1Light and OpticsHARD
A light ray falls on a face of an equilateral glass prism as shown (ray at 60° to the face normal). Which diagram correctly shows the complete path of the ray through the glass prism?

[Q73 · Apr · 2026]

Example 2Light and OpticsHARD
For a human eye, where u is the distance of an object from the eye, f is the focal length of the lens and v is the distance of image from the eye, which is the correct schematic graph ?

[Q128 · Apr · 2024]

Traps to expect

Distractor shapes specific to this chapter. The page-wide Traps section covers the bank-level patterns.

  • Sign-convention flip

    u with wrong sign, or f with wrong sign for a diverging lens/convex mirror, places v on the wrong side and often with the wrong magnitude. The wrong option matches the flipped sign.

  • TIR in the wrong direction

    TIR only DENSE→RARE. If the question describes light going from air→water and asks about TIR, the answer involves NO TIR (water is denser, so rare→dense).

  • Lens power units

    P = 1/f with f in METRES, not cm. f = 25 cm ⟹ f = 0.25 m ⟹ P = 4 D. Forgetting the conversion gives a factor-of-100 error.

Drill every light and optics question

97 questions from the bank, scoped to 6 bundled subtopics.

Drill the 97 questions

Related playbooks

Often paired with this one — drill these next if you found the worked examples above tractable.