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Challenging2 past questions

Reflection and refraction of light

Study how light rays behave at the interface between different media, including the laws of reflection and refraction, Snell's law, and related geometric considerations.

Why this shows up in the exam

NEET tests your understanding of how light bends and reflects at surfaces, which is fundamental to optics.

How NEET tests this

Numerical · 2 QsApplication

Learn the idea

Reflection follows i = r (incident = reflected) and refraction follows n₁sin i = n₂sin r. The key insight is that the angle between the reflected and refracted rays is simply i + r because they lie on opposite sides of the normal.

🧠 Memory hook: Think of the normal as a seesaw pivot: the incident and reflected rays sit on one side at equal angles, the refracted ray sits on the other side – the total spread is just the two angles added together.

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

Formulas & facts to keep ready

  • Law of reflection: angle of incidence = angle of reflection
  • Snell’s law: n₁ sin i = n₂ sin r
  • Angles are measured with respect to the normal
  • For a given interface, reflected ray stays in the first medium, refracted ray goes into the second
  • Critical angle exists when n₁ > n₂ and sin i_c = n₂/n₁

How to approach it

  1. 1Identify the refractive indices of the two media
  2. 2Use Snell’s law to find the angle of refraction r from the given i
  3. 3Recall that the reflected ray makes the same angle i with the normal
  4. 4Add i and r to obtain the angle between reflected and refracted rays
  5. 5Check if the result lies within 0°–180°

Worked example — watch it click

A light ray falls on a glass surface of refractive index √3, at an angle 60°. The angle between the refracted and reflected rays would be:

  • A)30°
  • B)60°
  • ✅90°
  • D)120°

The concept behind this problem

The problem requires you to apply Snell’s law to get r and then correctly combine i and r, testing both the law of refraction and the geometric relation for the angle between the two outgoing rays.

Step by step

  1. 1Given: n = √3, angle of incidence i = 60°.
  2. 2Using Snell's law: sin i / sin r = n, so sin r = sin 60°/√3 = (√3/2)/√3 = 1/2.
  3. 3Therefore r = 30°.
  4. 4The reflected ray makes angle 60° with normal (angle of reflection = angle of incidence).
  5. 5The refracted ray makes 30° with normal.
  6. 6Angle between reflected and refracted rays = 60° + 30° = 90°.

Watch out

Students often subtract i + r from 180°, giving the wrong angle; the correct angle is simply i + r.

Common slip-ups that cost marks

  • •Confusing the angle between the two rays with 180° − (i + r)
  • •Using the incident angle instead of the refracted angle in the sum
  • •Ignoring that the reflected ray stays in the original medium when applying Snell’s law

🌟 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 2NEET 2017

A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source I. When the mirror is rotated through a small angle θ, the spot of the light is found to move through a distance y on the scale. The angle θ is given by:

Push further

More challenging

3 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 3

A light ray strikes a plane mirror at an angle of incidence of 30 degrees. If the mirror is rotated by 5 degrees such that the angle of incidence increases, what will be the new angle between the incident ray and the reflected ray?

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