Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: Define refractive index, n, as the ratio of the speeds of a wave in two different regions
Learning Objective/s:
  • Define the refractive index as the ratio of wave speeds in two media.
  • Explain how the refractive index relates to the speed of light in a material.
  • Apply Snell’s Law using refractive indices to calculate refraction angles.
  • Predict the direction of ray bending based on relative refractive indices.
  • Solve numerical problems involving n, speed, and angle calculations.
Materials Needed:
  • Projector or interactive whiteboard
  • Slides with definitions, equations, and diagrams
  • Printed worksheet with practice problems
  • Ray‑tracing simulation (e.g., PhET)
  • Rulers and protractors for hands‑on activity
  • Calculator (or classroom calculators)
 Introduction:
Begin with a quick demonstration: shine a laser pointer through a glass of water and ask students what they observe. Recall that light changes speed when it enters a new medium, which leads to refraction. Today we will determine how the refractive index quantifies that speed change and use it to predict the bending of light.
Lesson Structure:
  1. Do‑Now (5') – Students answer: “What happens to a wave when it moves from air to water?” and share responses.
  2. Direct instruction (10') – Present the definition of refractive index, formulas n = c/v and n₁ sinθ₁ = n₂ sinθ₂, and typical values using slides.
  3. Guided practice (12') – Work through the air‑to‑water example together, calculating speed and refraction angle with Snell’s Law.
  4. Interactive simulation (8') – Students explore a ray‑tracing tool, vary n values, and record observed bending.
  5. Hands‑on activity (10') – Groups use protractors on printed diagrams to apply Snell’s Law to new media pairs.
  6. Check for understanding (5') – Quick exit‑ticket quiz with two short problems on n and angle calculation.
  7. Summary discussion (5') – Review key concepts and address common misconceptions.
Conclusion:
Summarise that the refractive index expresses how much light slows in a material and directly informs the angle change via Snell’s Law. For the exit ticket, each student writes one example of a material with a high n and predicts the ray’s behaviour. Homework: complete the worksheet with additional refraction problems.