Motors around us
Toy cars, hybrid and electric motor cars, electric trains and many other machines are driven by direct current (DC) motors.
Figure to be added
A real motor works on exactly the same idea as the coil, cell and magnet of activity 13.4: a coil carrying a current in a magnetic field feels a couple and turns. What changes is the engineering. A motor has to turn a load — the wheels of a car, the drum of a washing machine, the blades of a fan — so every part is made stronger and more efficient, and the crude half-stripped wire is replaced by a device that keeps the coil pushed all the way round.
| Part | Job |
|---|---|
| Armature | The coil wound on an iron core; turns when the current flows |
| Magnetic poles | Permanent magnets around the armature that give the field |
| Commutator (split rings) | Reverses the current in the coil every half turn |
| Brushes | Carry current from the outside circuit to the turning rings |
| Shaft | Turns with the armature and drives the load |
Why electric cars use motors
A petrol engine wastes much of its fuel's energy as heat, and it only produces useful turning force over a narrow range of speeds. An electric motor turns most of the electrical energy it is given into movement, gives a strong turning force from the moment it starts, and makes no exhaust where it runs. A hybrid car carries both a petrol engine and an electric motor, and uses whichever suits the moment. The DC motor on the next pages is the simplest kind; the big motors of trains work on the same principle.
A DC motor is a coil pushed round by a field
Toy cars, electric cars and electric trains run on DC motors, which turn a current-carrying coil in a magnetic field.