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Dispersion and Scattering of Light

NIOS · Class 12 · Physics

Quick revision notes for Dispersion and Scattering of Light — NIOS Class 12 Physics. Key concepts, formulas, and definitions for last-minute revision.

45 questions38 flashcards5 concepts

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Key Topics to Revise

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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.
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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.
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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.
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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).

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Full Notes

Key Concepts

Dispersion is the splitting of whiteThe refractive index μ ofWhen a ray PQ entersAs the angle of incidence iAngular Dispersion is the difference

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 Chapter Overview: Dispersion and Scattering of Light, Mind map showing the two major topics of the chapter — Dispersion and Scattering — with their key sub-concepts, Flowchart showing how white light entering a denser medium splits into colours due to different refractive indices for different wavelengths. These are the concepts NIOS Class 12 examiners draw on most — study them first, then practise related questions.
How to score full marks in Dispersion and Scattering of Light — NIOS Class 12 Physics?
Understand the core concepts first, then work through the 45 practice questions available for this chapter. Revise formulas and 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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