Physics · 9th Grade

Active learning ideas

Electric Motors and Transformers

Electric motors and transformers are abstract but foundational concepts that come alive when students manipulate real components. Active learning lets them see theory in action, turning equations like F = IL × B into observable motion and measurable voltages. Hands-on work also corrects misconceptions that textbooks alone cannot address.

• Common Core State Standards
• HS-PS2-5
• HS-ETS1-2

• 20–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Hexagonal Thinking
• 40 min · Small Groups

Motor Teardown: Identify the Parts

Provide groups with a salvaged or inexpensive DC motor. Students disassemble it, sketch each part, and label the armature, field magnets, commutator, and brushes. Each group explains to the class how their assigned component contributes to continuous rotation, with the teacher connecting explanations to the underlying force law.

How does a DC motor convert electrical energy into rotation?

Facilitation Tip

During Motor Teardown, have groups photograph each part before disassembly so they can reconstruct it mentally afterward.

What to look for

Present students with a diagram of a simple DC motor. Ask them to label the magnetic field, current direction, and the point where the commutator reverses current. Then, ask: 'What would happen to the motor's rotation if the commutator failed?'

• Analyze
• Evaluate
• Create
• Self-Awareness
• Relationship Skills

Activity 02

• Hexagonal Thinking
• 45 min · Pairs

Transformer Ratio Lab

Students wind two coils with different numbers of turns on a shared iron core and connect the primary to a low-voltage AC source. They measure input and output voltages, calculate the turns ratio, and compare it to the voltage ratio. A second trial uses a reversed coil assignment to see step-up vs. step-down behavior.

Why is high voltage used for long-distance power transmission?

Facilitation Tip

In the Transformer Ratio Lab, require students to record primary and secondary voltages at three different frequencies to see why 60 Hz is standard in the US.

What to look for

Pose the question: 'Imagine you are designing a power system for a remote village. Why would you choose to transmit electricity at a very high voltage and then step it down locally, rather than transmitting it at the voltage used by appliances?' Facilitate a discussion focusing on energy loss.

• Analyze
• Evaluate
• Create
• Self-Awareness
• Relationship Skills

Activity 03

• Think-Pair-Share
• 20 min · Pairs

Think-Pair-Share: Why Transmit at High Voltage?

Ask: if power equals IV, and we transmit 100MW, what current flows at 100kV versus at 100V? Students calculate both scenarios, compare the power lost in a transmission wire of fixed resistance using P = I²R, and share their conclusions. The dramatic numerical difference makes the engineering choice obvious.

How do transformers allow us to use different voltages for different appliances?

Facilitation Tip

For the Think-Pair-Share on high-voltage transmission, provide real-world loss data from utility websites to anchor the discussion in evidence.

What to look for

Give students a transformer with a primary coil of 100 turns and a secondary coil of 500 turns. If the input voltage is 120V, ask them to calculate the output voltage. Add the question: 'What happens to the current as the voltage is stepped up?'

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 04

• Gallery Walk
• 30 min · Small Groups

Gallery Walk: From Power Plant to Outlet

Set up six stations showing each stage of power delivery: generator, step-up transformer, transmission line, step-down substation, local distribution transformer, and household panel. Student groups annotate each station with the voltage level, reason for that voltage, and which principle (generation, transformation, or distribution) applies.

How does a DC motor convert electrical energy into rotation?

Facilitation Tip

In the Gallery Walk, assign each station a role (e.g., power plant engineer, homeowner) so students speak from perspective, not just facts.

What to look for

Present students with a diagram of a simple DC motor. Ask them to label the magnetic field, current direction, and the point where the commutator reverses current. Then, ask: 'What would happen to the motor's rotation if the commutator failed?'

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

A few notes on teaching this unit

Teach motors and transformers by starting with what students already know—household appliances—and then breaking them apart. Use analogies like a seesaw for torque and a gear train for voltage ratios, but always tie them back to the physics: F = IL × B and Faraday’s law. Avoid lecturing on the commutator; instead, let students see its effect when they remove it and observe the stalled coil. Research shows that students grasp conservation of energy better when they measure input and output power in a lab with measurable losses.

Students will confidently identify motor and transformer parts, explain why AC powers grids, and connect energy conservation to voltage-current transformations. Success looks like accurate labeling, clear reasoning in discussions, and correct calculations tied to physical behavior.

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Watch Out for These Misconceptions

• During Transformer Ratio Lab, watch for students who assume transformers work with any current type.

  Use the lab’s AC source and DC source side-by-side. When students apply DC, have them observe zero voltage on the secondary and relate it to the constant magnetic field. Ask them to explain why AC is essential in the lab report.

• During Transformer Ratio Lab, watch for students who think a step-up transformer creates more energy.

  Ask groups to calculate power on both sides using P = IV with measured values. When they see power stays nearly constant, prompt them to explain energy conservation in their lab notes.

• During Motor Teardown, watch for students who claim motors spin because magnets simply attract.

  After opening the commutator, have students manually rotate the coil and feel the change in resistance and direction. Ask them to describe how the commutator’s reversal converts push-pull into rotation in their exit ticket.

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Methods used in this brief

• Hexagonal Thinking
• Think-Pair-Share
• Gallery Walk