| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Physics |
| Lesson Topic: analyse graphs of the variation with time of potential difference, charge and current for a capacitor discharging through a resistor |
Learning Objective/s:
- Describe how charge, voltage and current decay exponentially during capacitor discharge.
- Derive and apply the expressions Q(t)=Q₀e⁻ᵗ/τ, V(t)=V₀e⁻ᵗ/τ, I(t)=I₀e⁻ᵗ/τ.
- Interpret the key features of Q‑t, V‑t and I‑t graphs, including the time‑constant markers.
- Calculate the time constant τ and use it to predict circuit behaviour at specific times.
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Materials Needed:
- Projector and slides showing derivations and graphs
- Whiteboard and markers
- Graph paper and rulers for each group
- Calculator or spreadsheet software
- Worksheet with example problem and practice questions
- Clickers or online polling tool for quick checks
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Introduction:
Begin with a real‑world hook (e.g., flash‑camera capacitor discharge) and ask students what they expect to happen to voltage over time. Review prior knowledge of exponential decay and Kirchhoff’s loop rule. State that by the end of the lesson they will be able to read and construct the three discharge graphs and extract quantitative information.
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Lesson Structure:
- Do‑now (5'): Sketch a generic exponential decay curve and label the initial point.
- Mini‑lecture (10'): Derive the differential equation, introduce τ = RC, and present the three solution formulas.
- Guided practice (10'): Solve the provided example (calculate τ, I(2τ), V(3τ) ) together on the board.
- Graphing activity (10'): In groups, plot Q(t), V(t) and I(t) on graph paper, marking t = τ, 2τ … 5τ.
- Misconception check (5'): Clicker quiz on common errors (constant current, dependence on V₀, etc.).
- Summary & exit ticket (5'): Each student writes one key takeaway and answers a short question about τ.
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Conclusion:
Recap the exponential nature of the discharge and the role of the time constant. Collect exit tickets to gauge understanding and assign a homework task: complete a worksheet that requires sketching the three graphs for a new set of C and R values and calculating τ.
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