Lesson Plan

• Describe the operation of a d.c. motor and the role of the split‑ring commutator and brushes.
• Explain how a magnetic field and current produce torque (motor effect) and why current reversal is required.
• Apply Fleming’s left‑hand rule to predict the direction of force on the armature.
• Analyse how voltage, load and magnetic flux influence motor speed and torque.

• Projector or interactive whiteboard
• Slide deck with motor diagram
• Simple d.c. motor demonstration kit
• Batteries and connecting wires
• Worksheets with torque equation and commutator diagram
• Carbon brush samples (optional)
• Whiteboard and markers

Show a short video of a toy motor spinning and ask students what makes it turn. Recall the magnetic field and Fleming’s left‑hand rule from previous lessons. Explain that today they will discover how a motor converts electrical energy into steady rotation and will be able to describe the commutator’s action, explain torque generation, and predict speed changes.

1. Do‑now (5'): Students answer a short question on the motor effect using the board.
2. Mini‑lecture (10'): Present the motor components, show a cross‑section diagram, and introduce the torque equation τ = N I A B sinθ.
3. Demonstration (10'): Unpack the d.c. motor kit, identify armature, magnets, commutator and brushes, and run it on a battery.
4. Guided inquiry (15'): In pairs, students trace the current path through the split‑ring commutator on a worksheet and explain why the current reverses each half‑turn.
5. Concept check (5'): Quick quiz (clickers or show of hands) addressing common misconceptions about magnetic fields and commutators.
6. Application activity (10'): Using the speed formula n = (V‑IR)/(kΦ), calculate how changing voltage or load affects motor speed.

Recap that the motor effect together with the split‑ring commutator produces continuous rotation by keeping torque direction constant. For the exit ticket, each student writes one sentence describing how the commutator maintains the same rotational sense. Homework: research a real‑world motor type and compare its commutator or electronic controller design with the simple d.c. motor studied today.