Prism: the angle of minimum deviation
"Prism: the angle of minimum deviation" is a free, interactive Class 12 Physics simulation for NEET and JEE, built on the lesson "Refraction through a prism" in Ray Optics and Optical Instruments. Change i and watch the dot on the δ–i graph. The deviation falls, bottoms out and rises again. In the shaded band no light comes out: it is totally reflected inside, at the second face. JEE Main asked 66 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Refraction through a prism in Ray Optics and Optical Instruments. Change the values and watch what happens.
In JEE Main
42 shifts analysed
66 questions from Ray Optics and Optical Instruments across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT § "Refraction through a Prism"
- For a prism of refracting angle A, the angles of refraction at the two faces satisfy r₁ + r₂ = A, and the deviation is δ = i + e − A.
- As the angle of incidence increases, the deviation first falls, reaches a minimum value D_m, and then rises again.
- At minimum deviation the ray passes symmetrically through the prism: i = e and r₁ = r₂ = A/2; for the usual isosceles or equilateral prism the ray inside then runs parallel to the base.
- Refractive index from minimum deviation: n₂₁ = sin[(A + D_m)/2] / sin(A/2).
- For a thin prism (small A), D_m = (n₂₁ − 1)A, so the deviation does not depend on the angle of incidence for small angles.
- Deviation depends on the refractive index of the prism relative to the surrounding medium; the same prism deviates light less when immersed in a liquid whose refractive index is lower than the prism's.
Questions
3 answers
- What does the "Prism: the angle of minimum deviation" simulation show?
- Change i and watch the dot on the δ–i graph. The deviation falls, bottoms out and rises again. In the shaded band no light comes out: it is totally reflected inside, at the second face.
- Does JEE Main ask questions from Ray Optics and Optical Instruments?
- Yes. JEE Main asked 66 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Refraction through a prism" in Ray Optics and Optical Instruments (Class 12 Physics).
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