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Exam level6 past questions

Polarization of light

Learn about the polarization of light, Brewster's law, Malus' law, and the use and function of polaroids.

Why this shows up in the exam

You need to recognize and calculate polarization effects, which are commonly tested in NEET.

How NEET tests this

Direct recall · 3 QsStatement analysis · 2 QsNumerical

Learn the idea

When light strikes a surface at Brewster's angle the reflected ray is completely plane‑polarized with its electric vector perpendicular to the plane of incidence (s‑polarization).

🧠 Memory hook: Brewster’s Brew: at the ‘brew‑time’ angle the reflected light goes ‘south’ (s‑polarized) while the refracted ray goes ‘north’ – they are at right angles.

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • Plane of incidence: the plane containing the incident and refracted rays
  • s‑polarized (perpendicular) and p‑polarized (parallel) components
  • Brewster's angle i_B = tan⁻¹(μ) where μ = n₂/n₁
  • At i_B the reflected and refracted rays are at 90°
  • Malus' law: I = I₀ cos²θ for a polarizer‑analyzer pair
  • A Polaroid transmits the component of E parallel to its transmission axis and absorbs the orthogonal component

How to approach it

  1. 1Identify if the question mentions the reflected and refracted rays being perpendicular – that signals Brewster's angle
  2. 2Compute i_B using tan⁻¹(μ) (or recognise the condition without calculation)
  3. 3State that the reflected ray is s‑polarized (E ⟂ plane of incidence)
  4. 4If intensity after a second polarizer is asked, apply Malus' law with the angle between transmission axes

Worked example — watch it click

Unpolarised light is incident from air on a plane surface of a material of refractive index µ. At a particular angle of incidence i, it is found that the reflected and refracted rays are perpendicular to each other. Which of the following option is correct for this situation?

  • A)i = sin⁻¹(1/µ).
  • ✅Reflected light is polarised with its electric vector perpendicular to the plane of incidence.
  • C)Reflected light is polarised with its electric vector parallel to the plane of incidence.
  • D)i = tan⁻¹(1/μ).

The concept behind this problem

The example asks which statement follows when reflected and refracted rays are perpendicular; recognizing this as Brewster's condition leads directly to the s‑polarization of the reflected beam.

Step by step

  1. 1When reflected and refracted rays are perpendicular, the angle of incidence is Brewster's angle: i = tan⁻¹(μ).
  2. 2At this angle, reflected light is completely plane polarized with electric vector perpendicular to the plane of incidence (s-polarization).
  3. 3This eliminates options (c) and (d).
  4. 4Option (a) gives sin⁻¹(1/μ) which would be the critical angle for total internal reflection (wrong context).
  5. 5The correct relation is i = tan⁻¹(μ), not tan⁻¹(1/μ) as in option (d).
  6. 6At Brewster's angle, reflected light has E-field perpendicular to plane of incidence.

Watch out

Choosing the parallel (p) polarization or the wrong angle formula (sin⁻¹ or tan⁻¹ of 1/μ).

Common slip-ups that cost marks

  • •Confusing Brewster's angle with the critical angle (sin⁻¹(1/μ))
  • •Mixing up s‑ and p‑polarization – reflected light is NOT parallel at Brewster's angle
  • •Using tan⁻¹(1/μ) instead of tan⁻¹(μ)

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 6NEET 1999

A polariser is used to

Push further

More challenging

8 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 8

Unpolarized light is incident on a transparent medium of refractive index 1.6 at Brewster's angle. Which of the following statements is true regarding the transmitted light?

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