Lesson Plan

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Lesson Plan
Grade: Year 12 Date: 17/01/2026
Subject: Physics
Lesson Topic: explain the meaning of the term diffraction
Learning Objective/s:
  • Describe diffraction as the bending and spreading of waves when they encounter an obstacle or aperture comparable to the wavelength.
  • Explain how Huygens’ principle leads to the formation of diffraction patterns.
  • Apply the single‑slit diffraction condition to predict the positions of minima.
  • Compare diffraction patterns with interference patterns and identify key differences.
  • Analyse everyday examples of diffraction and discuss its relevance to optical instrument design.
Materials Needed:
  • Projector and screen for displaying diagrams
  • Laser pointer and single‑slit apparatus
  • White screen or paper for observing diffraction patterns
  • Worksheet with practice problems
  • Calculator or computer for calculations
  • Handout summarising key equations
 Introduction:
Begin with a quick demonstration: shine a laser pointer at a hair and observe the faint diffraction pattern. Ask students what they notice and link it to prior learning about wave behavior. State that by the end of the lesson they will be able to define diffraction, explain its cause using Huygens’ principle, and predict pattern features.
Lesson Structure:
  1. Do‑now (5') – Students answer a short question on wave bending around obstacles on the worksheet.
  2. Mini‑lecture (10') – Define diffraction, show Huygens’ principle diagram, discuss key features.
  3. Demonstration (8') – Laser pointer with hair/single slit, observe pattern, record observations.
  4. Guided practice (12') – Work through the single‑slit minima formula using provided data; teacher circulates.
  5. Comparison activity (8') – Small groups fill a table contrasting diffraction vs interference.
  6. Check for understanding (5') – Quick quiz via clickers or show of hands.
  7. Summary discussion (5') – Review objectives and answer lingering questions.
Conclusion:
Recap the definition of diffraction, the condition for minima, and how it differs from interference. Have students complete an exit ticket stating one real‑world example of diffraction and one implication for optical design. Assign homework to solve two single‑slit diffraction problems and to locate a news article mentioning diffraction in technology.