Lesson Plan

• Describe how a smoothing capacitor reduces ripple in a rectified voltage.
• Explain the influence of capacitance value and load resistance on ripple magnitude.
• Calculate the required capacitance for a given ripple specification and load current.
• Evaluate practical considerations such as in‑rush current, voltage rating and capacitor ageing.

• Projector or interactive whiteboard
• Rectifier circuit kit (bridge rectifier, transformer)
• Electrolytic capacitors (100 µF – 2200 µF, 25 V)
• Resistors for load simulation (10 kΩ, 2 kΩ, 500 Ω)
• Multimeter or oscilloscope
• Worksheet with design problem
• Safety goggles

Begin with a short video showing a flickering lamp powered by a rectifier, asking students why the light is not steady. Recall the concepts of half‑wave and full‑wave rectification covered last week. State that by the end of the lesson they will be able to predict and control the ripple using a single capacitor.

1. Do‑now (5'): Quick quiz on rectifier types and ripple frequency.
2. Mini‑lecture (10'): Theory of capacitor‑input filtering and the key equations \(V_r \approx I_L/(fC)\) and \(\tau = R_LC\).
3. Live demonstration (8'): Compare waveforms of a half‑wave and full‑wave rectifier with and without a 100 µF capacitor on an oscilloscope.
4. Guided calculation (12'): Students work through the provided example to find the required capacitance for a 12 V supply delivering 100 mA with <0.5 V ripple.
5. Group design challenge (15'): Teams choose a capacitor value, justify their choice considering size, cost and in‑rush current, and record predictions.
6. Exit ticket (5'): One‑sentence answer to “What happens to ripple if the load resistance is halved?”

Summarise that larger capacitance and higher load resistance both lower ripple, but practical limits exist. Collect exit tickets and highlight the correct relationship between load resistance and ripple. Assign homework: design a 5 V regulator supply with a ripple < 0.2 V, specifying capacitor type and rating.