Activity 01
Lab Investigation: Disassemble and Analyze a DC Motor
Small groups carefully disassemble a hobby DC motor, identifying and sketching each component (armature, commutator, brushes, permanent magnets). Groups label how each part contributes to rotation, then reassemble and verify it still works by connecting it to a battery.
How does an electric motor use magnetic force to create rotation?
Facilitation TipDuring Lab Investigation: Disassemble and Analyze a DC Motor, provide each pair with a small motor, gloves, and a magnifying glass to locate the commutator and brushes before removing the housing.
What to look forPresent students with a diagram of a simple DC motor. Ask them to label the stator, rotor, commutator, and brushes. Then, have them explain in one sentence how the commutator ensures continuous rotation.
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Activity 02
Think-Pair-Share: Motor Versus Generator
Students are given a diagram of a DC motor and asked what would happen if, instead of connecting it to a battery, they spun the shaft by hand. Pairs discuss and predict before the teacher demonstrates using a hand-crank generator lighting an LED, making the reversibility immediate and concrete.
What is the role of a commutator in a DC motor?
Facilitation TipFor Think-Pair-Share: Motor Versus Generator, assign roles so one student draws the energy flow in a motor while the other draws it in a generator, then compare diagrams side-by-side.
What to look forPose the question: 'How is an electric car's motor acting as a generator when the driver lifts their foot off the accelerator?' Facilitate a discussion where students explain the energy transformation from kinetic to electrical energy and the role of electromagnetic induction.
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Activity 03
Energy Flow Diagram Activity
Groups trace the energy conversions in four systems: a gasoline car, a hybrid car, an EV with regenerative braking, and a hydroelectric plant. For each, they create a flow diagram showing input energy, useful energy output, and losses, then compare efficiency across systems.
How do regenerative braking systems in electric cars work as generators?
Facilitation TipIn Energy Flow Diagram Activity, require students to annotate each energy transfer with a numerical estimate or range to anchor abstract concepts in concrete values.
What to look forProvide students with two scenarios: 1) A wire carrying current is placed in a magnetic field. 2) A wire is moved through a magnetic field. Ask students to identify which scenario describes the principle of a motor and which describes a generator, and briefly explain why.
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Activity 04
Design Challenge: Why Does the Motor Need a Commutator?
Without explaining the commutator first, groups try to explain why a simple current loop in a fixed magnetic field would not spin continuously. Groups develop their own reasoning for what modification is needed, then compare proposals before the teacher introduces the actual commutator mechanism.
How does an electric motor use magnetic force to create rotation?
Facilitation TipDuring Design Challenge: Why Does the Motor Need a Commutator?, supply only a paperclip, two short wires, and a small magnet so students must physically simulate the reversal of current to maintain spin.
What to look forPresent students with a diagram of a simple DC motor. Ask them to label the stator, rotor, commutator, and brushes. Then, have them explain in one sentence how the commutator ensures continuous rotation.
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Generate Complete Lesson→A few notes on teaching this unit
Teach this topic by moving from the concrete to the abstract. Start with a disassembled motor so students see the commutator’s copper segments and brushes, then link that hardware to the timing of current reversal. Use hand-crank generators to let students feel the difference between effort to produce electricity and resistance when acting as a motor. Avoid launching straight into equations; let the physical experience drive the conceptual understanding first.
Students will explain how the same machine can act as a motor or generator by identifying key components and tracing energy flow. They will justify the commutator’s precise timing and quantify energy transfers in regenerative braking.
Watch Out for These Misconceptions
During Lab Investigation: Disassemble and Analyze a DC Motor, watch for students who treat the commutator as a decorative part rather than a timing device.
Ask students to rotate the armature slowly by hand and note when the brushes jump between segments. Have them mark those positions on a diagram and explain why current must reverse at those exact points to keep the coil spinning in the same direction.
During Design Challenge: Why Does the Motor Need a Commutator?, watch for students who believe any switch will work the same way.
Hand each group a paperclip switch and have them attempt to spin the armature by flipping the switch at different points in the rotation. Ask them to identify where their timing fails and relate that failure to the precise alignment required by the commutator.
During Energy Flow Diagram Activity, watch for students who assume regenerative braking recovers all kinetic energy.
Provide efficiency data from real hybrid cars and ask students to adjust their energy flow diagrams to reflect 60-70% recovery, labeling losses as heat, inverter inefficiency, and battery charge-discharge cycles.
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