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Syllabus

Dispersion and Scattering of Light — Syllabus

NIOS · Class 12 · Physics

What Dispersion and Scattering of Light covers in NIOS Class 12 Physics: 4 topics, for the 2026-27 session. Part of the NIOS Class 12 Physics syllabus.

45 questions38 flashcards12 formulas & key relations5 concepts

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4 Topics · NIOS Class 12 Physics · 2026-27

Topics in Dispersion and Scattering of Light

1

1. Dispersion of Light – Concept and Cause

  • White light (sunlight) is polychromatic – it consists of seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR), each with a different wavelength.
  • Visible light is a small part of the electromagnetic spectrum with wavelengths ranging from about 3.8 × 10⁻⁷ m (violet) to 7.8 × 10⁻⁷ m (red).
  • In vacuum and air, all colours travel with the same speed (3 × 10⁸ m/s) – so no separation occurs. Air and vacuum are called non-dispersive media.
2

2. Refraction Through a Prism – Angle of Deviation

  • Consider a triangular prism ABC with refracting angle A (= ∠BAC). A monochromatic ray PQ enters face AB and emerges as RS from face AC.
  • The angle between the incident ray PQ (produced forward) and the emergent ray RS is called the Angle of Deviation (δ).
  • r₁ and r₂ are angles of refraction at face AB and AC respectively. i is angle of incidence, e is angle of emergence.
3

3. Angular Dispersion and Dispersive Power

  • Different colours are deviated through different angles by the same prism. This difference in deviation is called Angular Dispersion.
  • Angular dispersion between violet and red: θ = δ_V − δ_R
  • Yellow light is taken as representative of average wavelength of the spectrum. Its deviation δ_Y is taken as the mean deviation.
4

4. Rainbow – Formation and Types

  • Rainbow is a beautiful natural example of dispersion and total internal reflection occurring together in water droplets suspended in the atmosphere.
  • You must have the Sun behind you to see a rainbow – the Sun, your eye, and the centre of the rainbow arc are collinear.
  • There are two types: Primary rainbow (brighter) and Secondary rainbow (fainter, above the primary).

Key Concepts

Central concept: Dispersion and Scattering of Light

Dispersion of LightRefraction Through a PrismMinimum DeviationSmall-Angle Prism FormulaDispersive Power (ω)Rainbow FormationScattering of LightRaman Effect

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Frequently Asked Questions

What are the important topics in Dispersion and Scattering of Light for NIOS Class 12 Physics?
Key topics in Dispersion and Scattering of Light include Dispersion of Light – Concept and Cause, Refraction Through a Prism – Angle of Deviation, Angular Dispersion and Dispersive Power, Rainbow – Formation and Types. Study these first, then practise questions on each for the NIOS Class 12 board exam.
How should I revise Dispersion and Scattering of Light for the NIOS Class 12 board exam?
Learn the core ideas first, then work through the 45 practice questions on Dispersion and Scattering of Light. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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