A ray of light passing through an equilateral prism is having velocity 2.12 × 10^8 m/s in the prism material, then the minimum angle of deviation is…
JEE Main 2026 — Physics Optics
2026mcqmedium
A ray of light passing through an equilateral prism is having velocity 2.12×108 m/s in the prism material, then the minimum angle of deviation is _________ degrees.
Official previous-year question
Held on 5 Apr 2026 · Verified 6 Jul 2026.
Options
A
45
B
30
C
28
D
58
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Solution
Velocity of light in vacuum, c=3×108 m/s
Velocity of light in the prism, v=2.12×108 m/s
Refractive index of the prism material, μ=vc=2.12×1083×108≈1.414≈2
For an equilateral prism, the angle of the prism A=60∘.
Using the prism formula:
μ=sin(2A)sin(2A+δm)
2=sin(30∘)sin(260∘+δm)
2=21sin(30∘+2δm)
sin(30∘+2δm)=22=21
30∘+2δm=45∘
2δm=15∘
δm=30∘
Answer: 30
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