Summary
A D.C. motor is a device that converts electrical energy into mechanical energy using direct current. It operates by passing a current through a coil in a magnetic field, causing it to spin due to the forces acting on the coil.
- Commutator — a device that reverses the direction of current in the coil every half turn. Example: Keeps the coil spinning by reversing the forces.
- Electromotive force (e.m.f.) — the voltage induced in a conductor when it cuts across magnetic field lines. Example: Induced when a wire moves through a magnetic field.
- Magnetic field — a region around a magnet where magnetic forces can be detected. Example: Created around a coil when current flows through it.
Exam Tips
Key Definitions to Remember
- Commutator: Reverses current direction every half turn.
- Electromotive force (e.m.f.): Voltage induced by cutting magnetic field lines.
Common Confusions
- Confusing the role of the commutator with that of slip rings.
- Misunderstanding the direction of current flow in the motor.
Typical Exam Questions
- What is the function of a commutator in a D.C. motor? It reverses the direction of current to keep the coil spinning.
- How is e.m.f. induced in a conductor? By moving the conductor through a magnetic field.
- What happens when the current direction in a coil is reversed? The magnetic field polarity is also reversed.
What Examiners Usually Test
- Understanding of how a D.C. motor operates.
- Ability to explain the role of the commutator.
- Knowledge of how e.m.f. is induced in a coil.