Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: Describe an experiment to show refraction of light by transparent blocks of different shapes
Learning Objective/s:
  • Describe the principle of refraction and Snell’s law.
  • Explain how the shape of a transparent block influences the path of a light ray.
  • Conduct the experiment to measure angles of incidence, refraction, emergence and calculate lateral shift or deviation.
  • Analyse data to determine refractive index and relate observations to theory.
  • Evaluate sources of error and suggest improvements.
Materials Needed:
  • Ray box or low‑power laser pointer
  • White paper sheet
  • Transparent rectangular slab (glass or Perspex)
  • Transparent triangular prism
  • Protractor or rotating platform with degree markings
  • Ruler or measuring scale
  • Pencil and eraser
  • Safety goggles (optional)
 Introduction:
Begin with a striking demonstration of a laser beam bending as it passes through a glass prism, asking students why the direction changes. Recall prior knowledge of light travelling in straight lines and the concept of speed change in different media. State that by the end of the lesson they will be able to design and analyse an experiment that quantifies this refraction.
Lesson Structure:
  1. Do‑now (5'): Students sketch a light ray hitting a flat surface and predict what happens when the surface is replaced by glass.
  2. Mini‑lecture (10'): Review refraction, Snell’s law and introduce the experiment apparatus.
  3. Demonstration set‑up (5'): Teacher arranges the ray box, paper, slab and prism, showing how to attach the protractor.
  4. Student investigation (20'): Groups perform the procedure – record angles for normal incidence, then increase i in 10° steps for both slab and prism, measuring emergence angles, lateral shift (slab) and deviation (prism).
  5. Data analysis (10'): Calculate r using Snell’s law, compute lateral shift d and deviation δ, discuss trends.
  6. Plenary (5'): Quick recap of findings; exit ticket – one sentence stating how block shape affects the ray’s path.
Conclusion:
Re‑emphasise that refraction occurs because light changes speed in different media, and that parallel‑faced blocks produce a lateral shift while prisms cause a measurable deviation. Students complete an exit ticket summarising the key observation and note any questions for homework. Assign a short task to plot sin i versus sin r from their data to estimate the refractive index of the material.