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Waves & Optics · Physics

Refraction is a direction change at a boundary.

Learn how the index of refraction controls bending, how to use Snell’s law, and why dispersion makes colors separate.

This topic

Refraction and Snell’s Law

Start with definitions, then build reliable geometry with angles measured from the normal.

Property
Index of refraction
The index of refraction describes how light propagates in a medium compared to vacuum. It summarizes how the medium affects wave speed.
  • Meaning of refractive index
  • Speed of light in a medium (conceptual)
  • Relative index between two media
  • Common values and intuition
Start nano-lesson Index links to speed in a medium.
Law
Snell’s law
Snell’s law relates the angles of incidence and refraction through the refractive indices. Correct angle definitions are essential.
  • Angles measured from the normal
  • Setting up Snell’s law correctly
  • Checking if a result is plausible
  • Special cases (normal incidence)
Start nano-lesson Draw the normal first.
Geometry
Bending of light
Refraction can bend light toward or away from the normal. Learn to predict the direction change before computing it.
  • Toward vs away from the normal
  • Higher vs lower index transitions
  • Ray diagrams at a flat boundary
  • Conceptual checkpoints for sign errors
Start nano-lesson Predict direction, then calculate.
Intro
Dispersion
In many materials, refractive index depends on wavelength. This causes different colors to refract by different amounts.
  • Wavelength dependence of index (conceptual)
  • Why prisms spread colors
  • Dispersion vs scattering (distinguish)
  • Where dispersion shows up in lenses
Start nano-lesson Index can depend on color.
Practice
Practice & Exercises
Practice predicting bend direction, applying Snell’s law, and explaining dispersion in simple contexts.
  • Angle-from-normal drills
  • Snell’s law computation sets
  • Toward/away prediction questions
  • Dispersion concept checks
  • Exam-style refraction problems
Open practice Always state indices and angles clearly.