Turning electricity into motion
An electric motor converts electrical energy into motion. Motors are everywhere: in fans, fridges, blenders, washing machines, power tools, toys, phones (the vibration motor), elevators and electric cars. A typical home has dozens of them.
The science behind motors
Motors use the connection between electricity and magnetism.
- Current makes magnetism. In 1820, Hans Christian Ørsted found that a wire carrying current makes a magnetic field around it. Coiling the wire makes a stronger field, an electromagnet.
- Magnets push and pull. Like poles repel; opposite poles attract.
- The motor effect. A wire carrying current inside a magnetic field feels a force. If the wire is part of a coil, the forces on opposite sides push in opposite directions, making the coil turn.
In 1821, Michael Faraday built the first device to make continuous motion from electricity.
Parts of a simple DC motor
| Part | Job |
|---|---|
| Stator (permanent magnets or field coils) | Provides a steady magnetic field |
| Armature (rotor) | Coil of wire that spins |
| Commutator | A split ring that reverses the current direction every half turn |
| Brushes | Carbon or metal contacts that touch the commutator and carry current in |
| Axle (shaft) | Turns with the armature and drives whatever the motor powers |
| Power source | Battery or power supply |
How it works, step by step
- Current flows from the battery through the brushes into the coil.
- The coil becomes an electromagnet, with north and south poles.
- Its poles are attracted to the opposite poles of the stator magnet and repelled by like poles, so the coil turns.
- Just as the coil’s poles line up with the opposite magnet poles, the commutator flips the current direction.
- The coil’s poles flip, so it’s pushed onward instead of stopping.
- This repeats over and over, keeping the motor spinning.
Without the commutator, the coil would just rock back and forth and stop.
Making a motor stronger or faster
| Change | Effect |
|---|---|
| More current | Stronger force; faster spin |
| More turns of wire on the coil | Stronger electromagnet |
| Stronger magnets | Stronger force |
| Iron core inside the coil | Concentrates the magnetic field |
Reversing the battery reverses the motor’s direction. That’s how a toy car goes forward and backward.
Types of motors
| Type | How it differs | Uses |
|---|---|---|
| Brushed DC motor | Uses brushes and a commutator | Toys, small appliances |
| Brushless DC motor | Uses electronics instead of brushes; longer lasting | Drones, computer fans, electric bikes |
| AC induction motor | Changing AC current creates a rotating field; no brushes | Fridges, fans, washing machines, factories |
| Stepper motor | Moves in small, precise steps | 3D printers, robots, cameras |
Nikola Tesla invented a practical AC induction motor in the 1880s. Today, induction motors are the most common motors in industry.
Motors and generators
A generator is a motor in reverse. Spin the coil in a magnetic field, and it produces electricity. Electric and hybrid cars use regenerative braking: when braking, the motor acts as a generator, recharging the battery instead of wasting energy as heat.
Efficiency
Electric motors are very efficient. Large motors can turn over 90% of electrical energy into motion. Gasoline engines manage only about 20–35%. This is one reason electric vehicles use energy much more efficiently.
Motors in daily life
- Kitchen: blender, mixer, fridge compressor, microwave turntable, dishwasher pump
- Home: fans, vacuum, washing machine, garage door, furnace blower
- Transport: electric cars, e-bikes, subways, power windows
- Devices: hard drives, phone vibration motors, cooling fans
Common mistakes
- Thinking motors make energy. They convert electrical energy; some is always lost as heat.
- Thinking the magnet spins. In a simple DC motor, the coil spins while the magnet stays still.
Try it yourself
- Build a simple homopolar motor with an AA battery, a strong neodymium magnet and a twisted copper wire (with an adult). Watch the wire spin.
- Wrap 30 turns of wire around a nail and connect a battery. How many paper clips can your electromagnet pick up? Try 60 turns.
- Take apart a broken toy motor (with an adult) and identify the magnets, coil, commutator and brushes.
Quick recap
- Motors turn electrical energy into motion.
- They rely on current creating magnetism and magnetic forces pushing on current-carrying wires.
- A DC motor has a stator, armature, commutator and brushes.
- The commutator keeps the coil spinning by reversing the current.
- Generators are motors in reverse; electric motors are highly efficient.