DC Motors

Active learning works well for DC motors because students need to see how abstract concepts like current direction and magnetic fields translate into physical motion. Hands-on building and testing make invisible forces visible and let students correct errors immediately through observation.

• Year 11
• Physics
• 4 activities
• 30 min–60 min

Learning Objectives

1. Explain the energy conversion process within a DC motor from electrical to kinetic energy.
2. Analyze the role of the commutator in reversing current direction to ensure continuous rotation.
3. Design a simple DC motor modification to increase its rotational speed.
4. Evaluate the impact of magnetic field strength and coil turns on the torque of a DC motor.

Problem-Based Learning

⏱ 50 min·Small Groups

Build and Test: Simple DC Motor

Provide coils, neodymium magnets, batteries, and split-ring commutators. Students assemble motors, observe rotation, and note direction changes. They measure spin rate with a timer and adjust components for smoother operation.

Prepare & details

Explain how a DC motor converts electrical energy into kinetic energy.

Facilitation Tip: During Build and Test: Simple DC Motor, circulate with a multimeter to help students measure current and voltage, linking readings to coil motion.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Problem-Based Learning

⏱ 40 min·Pairs

Investigation: Speed and Torque Factors

Vary current with resistors, swap magnet strengths, or alter coil turns. Pairs record RPM using a phone app and lifting force with a hooked mass. Graph results to identify trends and explain using motor effect equations.

Prepare & details

Analyze the function of the commutator in maintaining continuous rotation.

Facilitation Tip: During Investigation: Speed and Torque Factors, assign groups different variables to test so the class builds a collective dataset for analysis.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Problem-Based Learning

⏱ 60 min·Small Groups

Design Challenge: Optimised Motor

Challenge groups to modify a basic motor to lift the heaviest mass or spin fastest under load. Test prototypes, peer review designs, and present data on chosen variables like armature size.

Prepare & details

Design modifications to a simple DC motor to increase its speed or torque.

Facilitation Tip: During Design Challenge: Optimised Motor, provide a torque meter so teams can quantify their motor’s performance against their goal.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Problem-Based Learning

⏱ 30 min·Pairs

Demo Rotation: Commutator Flip

Use a large model with LED indicators to show current reversal. Whole class observes half-turn flips, then pairs replicate with mini versions, drawing force diagrams before and after commutator action.

Prepare & details

Explain how a DC motor converts electrical energy into kinetic energy.

Facilitation Tip: During Demo Rotation: Commutator Flip, freeze the rotation at key moments to highlight how current direction changes with commutator position.

Setup: Groups at tables with access to research materials

Materials: Problem scenario document, KWL chart or inquiry framework, Resource library, Solution presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management
• Relationship Skills

Teaching This Topic

Teach this topic by starting with the motor effect using a single wire and magnet to show force direction. Avoid rushing to the commutator; let students discover why a split ring is necessary after they see a coil flip back and forth. Research shows that drawing force diagrams on paper before building improves spatial reasoning, so include sketching exercises before each hands-on task.

What to Expect

Students will explain how the commutator maintains rotation, describe how changes in current or magnetic field affect torque and speed, and design a motor to meet a specific performance goal. Success shows when students connect theory to observed behavior and justify their design choices with evidence.

Watch Out for These Misconceptions

Common Misconception

During Build and Test: Simple DC Motor, watch for students who assume the coil will spin continuously without understanding the commutator’s role.

What to Teach Instead

Pause the class after the first failed attempt and ask groups to predict what will happen at the half-turn. Have them test the prediction by temporarily removing the commutator, then add it back and observe the difference in motion.

Common Misconception

During Investigation: Speed and Torque Factors, watch for students who think increasing voltage always increases both speed and torque equally.

What to Teach Instead

Guide students to plot speed and torque against voltage on the same graph. Ask them to explain why torque increases more under load while speed drops, using their data as evidence.

Common Misconception

During Demo Rotation: Commutator Flip, watch for students who believe the magnetic force acts uniformly around the coil.

What to Teach Instead

Use a compass to map the magnetic field around the coil during rotation. Have students sketch the field lines and predict where forces will cancel, then compare their predictions to the observed motion.

Assessment Ideas

Quick Check

After Build and Test: Simple DC Motor, give students a diagram of a DC motor and ask them to label the commutator, coil, and magnetic poles. Then have them draw arrows showing current and force directions at a given moment and explain their choices in pairs.

Discussion Prompt

After Investigation: Speed and Torque Factors, pose the question: 'What two changes would make your toy car go faster?' Have students discuss their ideas in groups, then share with the class, justifying their choices using data from their investigation.

Exit Ticket

After Demo Rotation: Commutator Flip, ask students to write a paragraph explaining how the commutator prevents the motor from oscillating. Require them to include the terms 'current direction' and 'magnetic field' and collect these to check for understanding before the next lesson.

Extensions & Scaffolding

• Challenge: Ask students to design a motor that runs on the lowest possible voltage, then test and compare results in a class showcase.
• Scaffolding: Provide pre-labeled motor diagrams and a word bank for students to complete during the Build and Test activity.
• Deeper: Introduce back-EMF and explain how it limits speed, then have students calculate expected vs. measured speeds using their motor data.

Key Vocabulary

Motor Effect	The phenomenon where a current-carrying conductor placed in a magnetic field experiences a force, causing movement.
Commutator	A rotating switch that reverses the direction of the electric current in the coil every half turn, enabling continuous rotation.
Torque	A twisting or turning force that causes rotation, influenced by factors like magnetic field strength and current.
Armature	The rotating part of an electric motor, typically consisting of coils of wire wound around an iron core.