Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Physics
Lesson Topic: recall and use Malus’s law ( I = I0 cos2θ ) to calculate the intensity of a plane-polarised electromagnetic wave after transmission through a polarising filter or a series of polarising filters (calculation of the effect of a polarising filter on the
Learning Objective/s:
  • Recall the definition of plane‑polarised light and the function of a polarising filter.
  • State Malus’s law and identify the correct angle to use.
  • Apply Malus’s law to single and multiple filters to calculate transmitted intensity.
  • Analyse common misconceptions about angle usage in successive filters.
  • Solve quantitative problems involving up to three polarising filters.
Materials Needed:
  • Projector or interactive whiteboard for diagrams.
  • Printed worksheet with worked examples and practice questions.
  • Set of Polaroid filters (or a simulation app) for a quick demonstration.
  • Scientific calculators for each student.
  • Whiteboard and markers.
 Introduction:
Begin with a 30‑second demonstration of two Polaroid sheets turning dark as they are rotated, prompting the question “Why does the light change?” Connect this to students’ prior knowledge of wave polarisation. Explain that by the end of the lesson they will be able to predict the intensity for any arrangement of filters using Malus’s law.
Lesson Structure:
  1. Do‑now (5'): Quick quiz on polarisation terminology from the previous lesson.
  2. Mini‑lecture (10'): Define plane‑polarised light, describe a polarising filter, derive Malus’s law.
  3. Demonstration (8'): Rotate Polaroid sheets, record intensity changes, discuss the angle‑dependence.
  4. Guided practice (12'): Work through Example 1 (single filter) and Example 2 (two filters) on the worksheet.
  5. Independent practice (10'): Students solve the three practice questions while the teacher circulates.
  6. Check for understanding (5'): Exit ticket – write Malus’s law and one condition for its correct use.
  7. Summary (5'): Recap key points and preview how the law extends to multiple filters.
Conclusion:
Review how the angle between the incident polarisation and each filter’s axis determines the transmitted intensity. Collect exit tickets to gauge mastery and assign a short homework task: calculate the intensity for a four‑filter arrangement with given angles. This reinforces the sequential application of Malus’s law.