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Saturday, 31 October

JEE Main 2021 · PhysicsNumerical answerNumerical valueMediumMulti-step

JEE Main 31 August 2021, Shift 2, Physics Q21

Question 21 of 90 in this shift, Physics question 21 of 30, Section B.

Cross-section view of a prism is the equilateral triangle ABC shown in the figure. The minimum deviation is observed using this prism when the angle of incidence is equal to the prism angle. The time taken by light to travel from P (midpoint of BC) to A is ________ ×10−10\times10^{-10} s. (Given, speed of light in vacuum =3×108= 3\times10^8 m/s and cos⁡30∘=32\cos30^\circ = \frac{\sqrt{3}}{2})

The figure, in words

Equilateral triangle ABC with A at the top, B bottom-left, C bottom-right; the two slanted sides AB and AC are each labelled 10 cm; P is a point on BC and a dotted line joins A to P.

Official answer

5

NTA final key.

Chapter
Ray Optics and Optical Instruments
Topic
Prism Deviation
Idea tested
Base Parallel Property at Minimum Deviation

Same topic in other shifts

All Prism Deviation questions
  1. 2 Apr 2026, Shift 1 · Q40For a thin symmetric prism made of glass (refractive index 1.51.5), the ratio of incident angle and minimum deviation will be _________.MediumSingle correct
  2. 2 Apr 2026, Shift 2 · Q41One side of an equilateral prism is painted by a transparent material of refractive index n2n_2. The refractive index of prism is 1.6. The…MediumSingle correctHas a figure
  3. 5 Apr 2026, Shift 1 · Q40A ray of light passing through an equilateral prism is having velocity 2.12×1082.12 \times 10^8 m/s in the prism material, then the minimum…MediumSingle correct
  4. 6 Apr 2026, Shift 2 · Q42Angle of minimum deviation is equal to the half of the angle of prism in an equilateral prism. The refractive index of the prism is…EasySingle correct
  5. 2 Apr 2025, Shift 2 · Q49A ray of light suffers minimum deviation when incident on a prism having angle of the prism equal to 60∘60^\circ. The refractive index of…EasyNumerical value
  6. 3 Apr 2025, Shift 1 · Q41Consider following statements for refraction of light through prism, when angle of deviation is minimum. A. The refracted ray inside prism…MediumOther

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.