A simple DC motor is a hands-on project that turns electrical energy from a battery into motion. It is built from a copper coil, a magnet, and two metal supports that act as both holders and electrical contacts. This project matters because it shows the same basic physics used in fans, electric cars, toys, and power tools.
Students can see current, magnetism, and force work together in a real device they can build on a tabletop.
When current flows through the copper coil, the coil becomes an electromagnet with a north and south pole. The magnetic field from the permanent magnet pushes on the current-carrying wire, creating a torque that makes the coil spin. A scraped or half-insulated end of the coil acts like a simple commutator, switching the current connection at the right time so the coil keeps rotating.
Changing the number of coil turns, magnet strength, battery voltage, and friction at the supports changes how well the motor runs.
Key Facts
- Motor effect: a current-carrying wire in a magnetic field experiences a force.
- Magnetic force on a straight wire: F = BIL when the wire is perpendicular to the magnetic field.
- Torque makes the coil rotate: torque = force x lever arm.
- More coil turns usually increase motor torque because each turn adds magnetic force.
- The right-hand rule gives force direction: fingers point with current, palm faces magnetic field direction, thumb points in force direction.
- A battery provides DC current, so the coil needs a commutator-like contact to keep spinning instead of stopping.
Vocabulary
- Armature
- The rotating coil of wire in a motor that carries current and experiences magnetic force.
- Direct current
- Direct current, or DC, is electric current that flows in one direction through a circuit.
- Magnetic field
- A magnetic field is the region around a magnet or current-carrying wire where magnetic forces can act.
- Torque
- Torque is a turning effect caused by a force acting at a distance from a rotation axis.
- Commutator
- A commutator is a contact system that reverses or interrupts current in a motor coil so rotation can continue.
Common Mistakes to Avoid
- Scraping all the insulation off both coil ends, which can make the coil receive current at the wrong times and stop instead of spinning. For many simple motors, one end is fully scraped and the other is scraped on only one side.
- Using weak electrical contacts, which prevents enough current from reaching the coil. The coil ends should rest lightly in the supports and touch clean metal.
- Placing the magnet too far from the coil, which makes the magnetic field at the coil too weak. Move the magnet close beneath the coil without letting it rub.
- Making the coil uneven or too heavy, which increases wobble and friction. A balanced circular coil with straight axle ends spins more easily.
Practice Questions
- 1 A motor coil has 20 turns. If each turn has 0.06 m of wire in the magnetic field and the current is 0.80 A in a 0.30 T field, what is the total magnetic force using F = NBIL?
- 2 A simple motor uses a 1.5 V battery and the coil resistance is 3.0 ohms. What current flows through the coil using I = V/R?
- 3 A student adds more turns to the coil but the motor spins more slowly. Explain how added torque, extra mass, and increased friction could all affect the result.