Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Physics
Lesson Topic: distinguish between root-mean-square (r.m.s.) and peak values and recall and use I r.m.s. = I0 / 2 and Vr.m.s. = V0 / 2 for a sinusoidal alternating current
Learning Objective/s:
  • Describe the difference between peak (maximum) and rms values of AC current and voltage.
  • Explain why rms values are used for power calculations in resistive circuits.
  • Apply the simplified conversion Ir.m.s. = I0/2 and Vr.m.s. = V0/2 to solve sinusoidal AC problems.
  • Identify common misconceptions about rms and peak values and correct them.
Materials Needed:
  • Projector or interactive whiteboard
  • Printed worksheet with waveform diagrams
  • Scientific calculators
  • Oscilloscope or AC demonstration kit
  • Formula sheet showing Ir.m.s. = I0/2 and Vr.m.s. = V0/2
 Introduction:
Begin with a quick demonstration of a sinusoidal waveform on the oscilloscope, asking students what the highest point represents. Recall that they have previously worked with peak values and DC equivalents. Explain that today they will learn how rms values provide an effective DC comparison and will be able to use the Ir.m.s. = I0/2 and Vr.m.s. = V0/2 shortcuts. Success will be shown by correctly converting given peak values and calculating average power.
Lesson Structure:
  1. Do‑now (5') – worksheet where students identify peak values from provided waveforms.
  2. Mini‑lecture (10') – definitions of peak and rms, why rms matters, and presentation of the Ir.m.s. = I0/2, Vr.m.s. = V0/2 relationships.
  3. Guided practice (12') – work through Example 1 (current) and Example 2 (voltage) together, using calculators.
  4. Collaborative activity (10') – pairs convert a set of peak values, compute power in resistors, and record results.
  5. Misconception check (8') – clicker quiz on common errors, followed by class discussion.
  6. Exit ticket (5') – students write one sentence summarising the rms‑peak relationship and solve a new conversion problem.
Conclusion:
Review that rms values give the equivalent DC current or voltage for power calculations and that for sinusoidal waveforms the shortcut is dividing the peak by two. Students submit an exit ticket showing a conversion and a brief explanation. For homework, assign a set of AC problems requiring the use of the rms‑peak relationship.