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Saturday, 10 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctHardMulti-step

JEE Main 9 January 2020, Shift 2, Physics Q17

Question 17 of 75 in this shift, Physics question 17 of 25, Section A.

There 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 sectional surface area. Neglecting any reflection from the bottom and absorption by water, percentage of light that emerges out of surface is (nearly) : [Use the fact that surface area of a spherical cap of height hh and radius of curvature rr is 2πrh2\pi rh]
  1. (1)50%
  2. (2)34%
  3. (3)21%
  4. (4)17%Official answer

Official answer

Option 4

NTA final key (Jan 2020).

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

Same idea in other shifts

Asked 6× 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 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
  5. 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

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. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.