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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumMulti-step

JEE Main 25 July 2021, Shift 2, Physics Q16

Question 16 of 90 in this shift, Physics question 16 of 30, Section A.

A ray of light entering from air into a denser medium of refractive index 43\frac{4}{3}, as shown in figure. The light ray suffers total internal reflection at the adjacent surface as shown. The maximum value of angle θ\theta should be equal to :

The figure, in words

A rectangular block (open at the bottom) with medium marked μ=43\mu=\frac{4}{3}. A ray comes in from the upper right to a point on the top surface, making angle θ\theta with the dashed normal (arrow directed toward the surface). Inside, the refracted ray goes down-left making angle θ′\theta' with the dashed normal and hits the left vertical surface; there the angle θ′′\theta'' is marked between the ray and a horizontal dashed line (normal to that surface). The ray then leaves the left surface going down and to the right.
  1. (1)sin⁡−153\sin^{-1}\frac{\sqrt{5}}{3}
  2. (2)sin⁡−173\sin^{-1}\frac{\sqrt{7}}{3}Official answer
  3. (3)sin⁡−174\sin^{-1}\frac{\sqrt{7}}{4}
  4. (4)sin⁡−154\sin^{-1}\frac{\sqrt{5}}{4}

Official answer

Option 2

NTA final key.

Chapter
Ray Optics and Optical Instruments
Topic
Refraction and Snell's Law
Idea tested
Total Internal Reflection

Same idea in other shifts

Asked 9× in all
  1. 7 Apr 2025, Shift 2 · Q42A transparent block A having refractive index μ=1.25\mu=1.25 is surrounded by another medium of refractive index μ=1.0\mu=1.0 as shown in figure.…MediumSingle correctHas a figure
  2. 8 Apr 2024, Shift 1 · Q43Critical angle of incidence for a pair of optical media is 45∘45^\circ. The refractive indices of first and second media are in the ratio:EasySingle correct
  3. 11 Apr 2023, Shift 1 · Q35The critical angle for a denser-rarer interface is 45∘45^\circ. The speed of light in rarer medium is 3×1083 \times 10^8 m/s. The speed of…EasySingle correct
  4. 25 Jun 2022, Shift 1 · Q44A light wave travelling linearly in a medium of dielectric constant 4, incidents on the horizontal interface separating medium with air.…MediumSingle correct
  5. 22 Jul 2021, Shift 2 · Q3A ray of light passes from a denser medium to a rarer medium at an angle of incidence ii. The reflected and refracted rays make an angle…MediumSingle correctHas a figure
  6. 25 Jul 2021, Shift 1 · Q9A ray of laser of a wavelength 630 nm is incident at an angle of 30∘30^\circ at the diamond-air interface. It is going from diamond to air.…EasySingle correct
  7. 8 Jan 2020, Shift 1 · Q15The critical angle of a medium for a specific wavelength, if the medium has relative permittivity 3 and relative permeability…MediumSingle correct
  8. 9 Jan 2020, Shift 2 · Q17There is a small source of light at some depth below the surface of water (refractive index =43= \frac{4}{3}) in a tank of large cross…HardSingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.