Lesson Plan

• Recall the definition of the time constant τ = RC for a discharging capacitor.
• Explain how charge and voltage decay exponentially with time.
• Apply the discharge equation V(t)=V₀e⁻ᵗ/τ to calculate voltage after a given interval.
• Determine τ for specified R and C values and interpret its physical meaning.
• Identify common errors when using the time‑constant formula.

• Projector and screen
• Whiteboard and markers
• Printed worksheet with practice questions and summary table
• Digital simulation (e.g., PhET capacitor‑discharge app)
• Calculators
• Graph paper

Begin with a quick demonstration of a camera flash to highlight how quickly a capacitor can release stored energy. Review students’ prior knowledge of Ohm’s law and basic RC circuits, then state that today they will master the time‑constant τ = RC and use it to predict discharge behaviour. Success will be measured by correctly solving a discharge problem and explaining the meaning of τ.

1. Do‑now (5'): short quiz on charge, voltage, and Ohm’s law.
2. Mini‑lecture (10'): derive the discharge equation and introduce τ = RC.
3. Guided example (8'): calculate τ and V(t) for a 10 µF capacitor and 2 kΩ resistor.
4. Simulation activity (10'): students manipulate R and C in the PhET app, record voltage decay curves, and note the 37 % point.
5. Partner practice (12'): work through three practice questions from the source notes.
6. Check for understanding (5'): exit‑ticket – write the definition of τ and one real‑world example.

Summarise that τ = RC sets the timescale for exponential decay, with the voltage falling to ~37 % after one τ and effectively zero after 5 τ. Collect exit‑tickets to gauge mastery and assign homework: three additional discharge problems requiring calculation of τ and voltage at specified times.