| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: derive, using Kirchhoff’s laws, a formula for the combined resistance of two or more resistors in parallel |
Learning Objective/s:
- Apply Kirchhoff’s Current and Voltage Laws to analyze parallel circuits.
- Derive the formula for equivalent resistance of two resistors in parallel.
- Generalise the derivation to n resistors in parallel.
- Use the derived formula to solve numerical problems involving parallel networks.
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Materials Needed:
- Projector or interactive whiteboard
- Circuit simulation software (e.g., PhET)
- Set of resistors and a DC power supply for demo
- Worksheets with derivation steps and practice problems
- Calculator
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Introduction:
Begin with a quick demonstration of a simple parallel circuit lighting two LEDs, prompting students to predict the total current. Review prior knowledge of Ohm’s law and Kirchhoff’s laws, emphasizing how currents split at a junction. State that by the end of the lesson they will be able to derive and apply the parallel‑resistance formula.
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Lesson Structure:
- Do‑now (5'): Solve a short series‑resistance problem to activate prior knowledge.
- Mini‑lecture (10'): Review KCL, KVL, and Ohm’s law with board examples.
- Guided derivation (15'): Walk through the two‑resistor derivation; students complete missing algebra on a worksheet.
- Extension activity (10'): In pairs, use the general formula to calculate equivalent resistance for 3‑4 resistors using the simulation.
- Check for understanding (5'): Exit ticket – write the final formula and a brief explanation of the reciprocal‑sum concept.
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Conclusion:
Summarise that the equivalent resistance of parallel branches is found by summing the reciprocals of each resistor and taking the reciprocal of the total. Ask a few students to share their exit‑ticket answers for immediate feedback. Assign homework to solve five mixed‑circuit problems applying the derived formula.
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