📖 In-Depth Theory
How a DC Electric Motor Works
A DC ELECTRIC MOTOR converts electrical energy into kinetic energy (rotation).
KEY COMPONENTS:
Rectangular COIL of wire — sits between the poles of a magnet.
SPLIT-RING COMMUTATOR — a ring split into two halves, connected to the coil ends.
BRUSHES — stationary carbon contacts that touch the commutator and connect to the power supply.
HOW IT ROTATES:
1. Current flows through the coil via the brushes and commutator.
2. The motor effect creates a FORCE on each side of the coil (F = BIl).
3. The forces on opposite sides of the coil are in OPPOSITE DIRECTIONS → creates a turning force (TORQUE).
4. The coil rotates.
WHY IT KEEPS ROTATING — THE COMMUTATOR:
Without the commutator: after rotating 90°, the coil would reach vertical — the forces become parallel to the coil plane → no more torque → coil would oscillate, not spin continuously.
The SPLIT-RING COMMUTATOR swaps the current direction in the coil every half turn → forces always push the coil in the same rotation direction → continuous rotation.
Increasing Motor Speed and Torque
The SPEED and TORQUE (turning force) of a DC motor can be increased by:
INCREASING THE CURRENT:
More current → larger motor effect force (F = BIl) → more torque → faster rotation.
INCREASING THE MAGNETIC FLUX DENSITY:
Stronger magnetic field → larger force → more torque.
Use stronger permanent magnets or increase current in electromagnet.
INCREASING THE NUMBER OF TURNS in the coil:
More turns → total force multiplied by number of turns → much more torque.
ADDING AN IRON CORE inside the coil:
Concentrates and strengthens the magnetic field within the coil → more efficient motor.
REAL DC MOTORS:
Use many coils wound at different angles around an iron cylinder (ARMATURE).
Gives smoother rotation and more consistent torque.
Multiple commutator segments and brushes.
Applications of Electric Motors
Electric motors are found in almost every electrical device that involves rotation:
CONSUMER ELECTRONICS:
Hard disk drives, cooling fans, disc drives, washing machines, vacuum cleaners.
TRANSPORT:
Electric vehicles: battery-powered motor → no combustion → zero direct emissions.
Hybrid cars: electric motor + petrol engine.
Electric trains, trams, lifts.
INDUSTRY:
Conveyor belts, pumps, compressors, CNC machine tools.
MEDICAL:
Surgical drills, ventilators, infusion pumps.
ADVANTAGES of electric motors over combustion engines:
Highly EFFICIENT (>90% vs ~25-35% for petrol engines).
Instant torque — maximum torque from standstill.
No direct exhaust emissions.
Simple, reliable — fewer moving parts.
Can act as GENERATORS during braking (regenerative braking — recovers KE back to electrical store).
REGENERATIVE BRAKING:
Motor reversal — when slowing, the motor acts as a generator.
KE → electrical energy → stored in battery.
Reduces brake wear and improves overall efficiency.
⚠️ Common Mistake
The SPLIT-RING COMMUTATOR swaps the current direction every half turn — this is what makes a DC motor spin continuously rather than oscillating. Without the commutator, the coil would rock back and forth. The commutator is unique to DC motors — AC motors use a different mechanism.