Lesson Plan

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Lesson Plan
Grade: Date: 01/12/2025
Subject: Physics
Lesson Topic: Magnetic fields
Learning Objective/s:
  • Describe how a changing electric field generates a magnetic field during the discharge of a capacitor (Maxwell–Ampère law).
  • Derive the expressions for the magnetic field inside and outside a discharging capacitor as functions of time and distance.
  • Apply the RC time‑constant to calculate magnetic‑field values for given circuit parameters.
  • Analyse common misconceptions about displacement current and magnetic fields in capacitors.
Materials Needed:
  • Projector and screen for diagram slides.
  • Whiteboard and markers.
  • Printed worksheet with RC‑circuit diagram and practice problems.
  • Resistor, capacitor, and switch for a quick demonstration circuit.
  • Multimeter (optional) to measure transient current.
  • Scientific calculators for exponential calculations.
 Introduction:
Begin with a striking demonstration of a capacitor discharge and ask students what they expect to happen to the magnetic field. Recall prior learning on Ohm’s law, RC time constants, and Ampère’s law. State that by the end of the lesson they will be able to predict and calculate the magnetic field produced during discharge.
Lesson Structure:
  1. Do‑now (5'): Students sketch a simple RC circuit and list known equations (Q = CV, I = dQ/dt).
  2. Mini‑lecture (10'): Derive the differential equation for discharge and introduce the concept of displacement current.
  3. Guided derivation (12'): Work through the Maxwell‑Ampère law to obtain B‑field expressions inside and outside the capacitor, using a circular Amperian loop.
  4. Hands‑on demo (8'): Set up the RC circuit, trigger discharge, and discuss the transient current and associated magnetic field (qualitative).
  5. Practice problems (10'): Students solve a numerical example (similar to the one in the notes) and check answers in pairs.
  6. Misconception check (5'): Quick poll on common errors; clarify why the magnetic field does not vanish.
  7. Exit ticket (5'): Write one correct statement and one corrected misconception about magnetic fields in a discharging capacitor.
Conclusion:
Recap the link between changing electric fields and magnetic fields, emphasizing the derived B‑field formulas. Collect exit tickets to gauge understanding, and assign a homework task to calculate the magnetic field for a different RC combination and to explain the effect of reversing the capacitor polarity.