Physics · 12th Grade

Active learning ideas

Applications of Magnetic Forces: Motors and Galvanometers

Active learning works here because students can directly observe torque, rotation, and energy conversion—key ideas that are often abstract in textbooks. Building, measuring, and troubleshooting real devices makes the connection between magnetic force and mechanical motion immediate and memorable.

• Common Core State Standards
• HS-PS2-5

• 25–70 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Simulation Game
• 70 min · Small Groups

Build-a-Motor Lab

Teams construct a simple brushed DC motor from a D-cell battery, copper wire, two neodymium magnets, and foam blocks. Students troubleshoot why their motor starts, stalls, or spins inconsistently, and document which magnetic force interactions are responsible for each behavior.

Explain the operating principles of a DC electric motor based on magnetic forces.

Facilitation Tip

During Build-a-Motor Lab, circulate with a multimeter to catch short circuits early and redirect students to check polarity before rewinding their coils.

What to look for

Present students with a diagram of a simple DC motor. Ask them to label the magnetic field, the current-carrying coil, and the commutator. Then, ask them to write one sentence explaining how the commutator ensures continuous rotation.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 02

• Think-Pair-Share
• 25 min · Pairs

Think-Pair-Share: Galvanometer to Ammeter

Students examine a basic galvanometer diagram and a shunt resistor schematic, then predict how adding the shunt converts the galvanometer to an ammeter. Pairs compare reasoning before testing the prediction with a circuit simulation.

Analyze how the design of a galvanometer allows it to measure electric current.

Facilitation Tip

In Think-Pair-Share: Galvanometer to Ammeter, assign roles so one student sketches the circuit while the other annotates current flow and deflection direction.

What to look for

Pose the question: 'Imagine you have a basic galvanometer that is not sensitive enough to measure the current from a small solar cell. What two components could you adjust, and how, to increase its sensitivity?' Facilitate a class discussion where students justify their proposed modifications.

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

Activity 03

• Gallery Walk
• 35 min · Small Groups

Gallery Walk: Inside Electric Devices

Stations feature cutaway diagrams of a car starter motor, a handheld drill, and an analog voltmeter. Groups identify the coil, magnet, and commutator or restoring spring in each device and describe how magnetic torque drives or measures in that specific application.

Design improvements to an electric motor to increase its efficiency or torque output.

Facilitation Tip

On the Gallery Walk: Inside Electric Devices, ask each group to choose one motor or galvanometer to trace the energy path from input to output and post it next to their display.

What to look for

Students write down the primary function of an electric motor and the primary function of a galvanometer. They then provide one example of a product or device where each is used.

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

A few notes on teaching this unit

Teachers should anchor the unit in hands-on construction first, using simple motors and galvanometers to reveal the physics rather than starting with equations. Avoid diving into torque formulas until students have felt the force on a current-carrying wire with their own hands. Research shows that students who build and test their own devices retain the distinction between motors and generators better than those who only analyze diagrams.

Students will leave able to explain how a current-carrying loop in a magnetic field produces torque, how a commutator maintains one-way rotation, and how galvanometers respond to current rather than voltage. They will also distinguish motors from generators and justify design choices for sensitivity in measuring devices.

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Watch Out for These Misconceptions

• During Build-a-Motor Lab, watch for students who believe the motor is creating energy. Redirect them by having them measure the battery voltage before and after starting the motor and calculate the energy drop.

  Connect a multimeter in parallel with the motor and have students observe the voltage drop when the motor starts spinning; use this data to discuss energy conversion from electrical to kinetic.

• During Build-a-Motor Lab, watch for students who claim a motor and generator are fundamentally different. Redirect them by having them spin the motor shaft by hand and measure the voltage generated on the same multimeter.

  Use the same hobby motor, battery, and multimeter to show that it can act as both a motor and a generator, reinforcing the dual-role concept with direct evidence.

• During Think-Pair-Share: Galvanometer to Ammeter, watch for students who think the galvanometer deflects due to voltage. Redirect them by having them add series resistors and observe how deflection changes with current.

  Provide different resistors and ask students to predict and then measure how current changes while voltage across the galvanometer stays nearly constant, isolating current as the controlling variable.

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Methods used in this brief

• Simulation Game
• Think-Pair-Share
• Gallery Walk