Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Physics
Lesson Topic: understand the conditions required if two-source interference fringes are to be observed
Learning Objective/s:
  • Describe the seven conditions required for observable two‑source interference fringes.
  • Explain how each condition influences fringe visibility and contrast.
  • Apply the fringe‑spacing formula β = λD/d to predict fringe separation in a double‑slit setup.
  • Design a simple laboratory arrangement that satisfies coherence and geometry requirements.
  • Analyse experimental data to evaluate whether the conditions have been met.
Materials Needed:
  • Laser pointer or narrow‑band LED with filter
  • Double‑slit mask (slit width <0.1 mm, separation a few mm)
  • Rigid optical bench and mounts
  • Screen or white paper for observing fringes
  • Polaroid sheet (to check polarisation)
  • Ruler or digital caliper
  • Worksheet with calculation tasks
 Introduction:
Begin with a striking video of colourful interference patterns to spark curiosity. Ask students what they think determines the sharpness of those patterns, linking to prior knowledge of wave superposition. State that by the end of the lesson they will be able to identify and test the specific conditions needed for clear two‑source fringes.
Lesson Structure:
  1. Do‑now (5'): Students list factors that could blur interference patterns; teacher collects responses.
  2. Mini‑lecture (10'): Present the seven conditions with diagrams and brief explanations.
  3. Demonstration (15'): Set up a double‑slit experiment; vary one condition at a time (e.g., replace laser with white light) and discuss observed changes.
  4. Group activity (10'): Using given λ, D, and d values, students calculate expected fringe spacing and then measure it on the screen.
  5. Concept check (5'): Quick Kahoot quiz matching scenarios to the violated condition.
  6. Summary discussion (5'): Whole‑class recap of key points and clarification of any misconceptions.
Conclusion:
Recap the seven conditions and emphasise how each was demonstrated during the lab. Students complete an exit ticket stating which condition they consider most critical and why. Assign homework to research a real‑world application (e.g., holography or fiber optics) where maintaining these conditions is essential.