| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: recall and use the fact that the mean power in a resistive load is half the maximum power for a sinusoidal alternating current |
Learning Objective/s:
- Describe the relationship between peak power and mean power for a resistive load with sinusoidal AC.
- Derive the mean‑power formula using sinusoidal expressions and the identity sin²x = (1‑cos2x)/2.
- Apply RMS concepts to calculate mean power in resistive circuits.
- Solve numerical problems using both the half‑maximum rule and RMS formulas.
- Identify common misconceptions about average versus RMS power.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Worksheet with derivation steps and practice questions
- Scientific calculators
- Handout of the summary table (peak, RMS, mean power)
- PhET AC circuit simulation (or function‑generator demo)
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Introduction:
Begin with a striking animation of a sinusoidal voltage waveform and ask students how they would compare its power to a DC source. Review prior knowledge of peak values and RMS definitions. State that by the end of the lesson they will be able to predict mean power using the “half‑maximum” rule and verify it with RMS calculations.
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Lesson Structure:
- Do‑now (5'): Quick quiz on peak vs RMS values and previous AC concepts.
- Mini‑lecture (10'): Derive \(\overline{P}=V_{\max}I_{\max}/2\) and connect to RMS formula \(\overline{P}=I_{\text{rms}}^{2}R\).
- Guided example (10'): Work through the 10 Ω resistor problem, students follow on worksheet.
- Interactive simulation (8'): Use PhET to vary \(V_{\max}\) and observe the instantaneous‑power curve, discuss the half‑maximum result.
- Practice questions (12'): Pairs solve the three provided problems; teacher circulates for feedback.
- Misconception check (5'): Click‑question on “average vs RMS” to expose common errors.
- Summary & exit ticket (5'): Students write one key takeaway and answer a short calculation on an exit slip.
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Conclusion:
Recap the half‑maximum relationship and its equivalence to RMS‑based power expressions. Collect exit tickets to gauge understanding and assign homework: complete a set of additional AC‑power problems from the textbook. Remind students to bring their calculators for the next lesson on non‑resistive loads.
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