Lesson Plan

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Lesson Plan
Grade: Year 12 Date: 25/02/2026
Subject: Physics
Lesson Topic: describe the use of a diffraction grating to determine the wavelength of light (the structure and use of the spectrometer are not included)
Learning Objective/s:
  • Describe the principle of a diffraction grating and state the grating equation.
  • Calculate the wavelength of monochromatic light from measured diffraction angles.
  • Analyse common sources of error and propose mitigation strategies.
  • Select an appropriate grating specification for a given resolution requirement.
  • Interpret experimental data to justify the calculated wavelength.
Materials Needed:
  • Diffraction grating (e.g., 600 lines mm⁻¹)
  • Laser pointer or other monochromatic light source
  • Screen or detector
  • Protractor or spectrometer angular scale
  • Ruler/measuring tape
  • Data worksheet
  • Projector for mini‑lecture
 Introduction:
Begin with a quick question on interference patterns to activate prior knowledge. Explain that today’s focus is using a diffraction grating as a quantitative tool for wavelength measurement. Outline the success criteria: students will be able to predict, measure, and calculate λ, and evaluate experimental accuracy.
Lesson Structure:
  1. Do‑now (5 min): Short worksheet on constructive interference and order numbers.
  2. Mini‑lecture (10 min): Explain grating principle, spacing d, and the equation d sin θ = nλ with visual slides.
  3. Demonstration (10 min): Set up the grating, shine the laser, measure first‑order angles on both sides, record data.
  4. Guided calculation (10 min): Students use the worksheet to compute λ from their measurements.
  5. Error‑analysis discussion (8 min): Identify systematic and random errors; suggest mitigations.
  6. Extension activity (7 min): Compare results using a finer (1200 lines mm⁻¹) grating.
  7. Exit ticket (5 min): Write one key takeaway and one remaining question.
Conclusion:
Recap how the grating equation links measured angles to wavelength and highlight the importance of accurate alignment and spacing. Collect exit tickets to gauge understanding and assign a homework task: students research a real‑world application of diffraction gratings and prepare a brief summary.