L33. Electric Motors and Generators

Magnetism

R-report

L33. Electric Motors and Generators

Why does turning a crank on a flashlight make a light, and why does a toy motor spin when you give it a battery?

A quick observation: the hand-crank flashlight

Try a hand-crank flashlight or look at a simple bicycle dynamo. When you turn the crank, a tiny bulb or LED lights without batteries. Turn the crank faster and the light grows brighter. This neat trick links motion, magnets, and conductors. You don’t need to know everything about magnets again — you’ve already learned magnetic fields and the basics of electromagnetism — but here we use that earlier idea: moving conductors near magnetic fields makes electricity, and pushing an electric current through a conductor in a magnetic field can produce a push (a force). In everyday tools the same parts are used in two opposite ways: one set-up makes motion from electricity (a motor) and the other makes electricity from motion (a generator). Studying the flashlight connects these two devices: it is a generator you power with your hand.

How a basic DC motor turns

A simple direct-current (DC) motor uses a loop of wire (a coil) placed between magnets. When you send electric current through the coil, the magnetic field around the coil interacts with the magnets’ field and the coil feels a sideways push. That push makes the coil start to spin. To keep spinning in one direction, small parts called a commutator and brushes swap which side of the coil gets current at the right time so the force keeps turning the coil instead of reversing it. This is why toy motors keep rotating smoothly when powered.

• Components: coil (armature), permanent magnets, commutator, brushes, axle. Sequence: current → magnetic interaction → sideways force on coil → coil turns → commutator reverses current at half turn → continuous rotation.

How moving coils make electricity (the generator)

A generator is the motor’s partner that runs backwards. If you physically turn the coil inside the magnetic field, electrons in the wire are pushed and a current flows in the circuit — the faster the turn, the larger the current. Important practical pieces: the same coil and magnets can make electricity when moved, and the commutator or a slip-ring keeps the connection to the outside circuit as the coil spins. A quick classroom investigation: connect a small coil to a sensitive meter or LED and spin it between two magnets. You’ll see a pulse of current each half turn. That demonstrates the core principle: motion in a magnetic field produces electricity.

• Conditions that produce current: a conductor moving relative to a magnetic field, and a closed circuit path for charge to flow. Observable effect: faster motion or stronger magnets → bigger electrical output.

Motor vs generator: energy and real-world links

The practical difference is energy direction. Motors convert electrical energy into mechanical energy (they make things move). Generators convert mechanical energy into electrical energy (they make current you can use). Think of a bicycle: pedals deliver mechanical energy, a dynamo/generator on the wheel converts that to electricity to power a light. An electric scooter’s motor uses electricity from a battery to turn the wheels and move you. Both devices often contain the same core parts — coils, magnets, and a way to keep electric contact while something spins — but the input and output energy types are swapped. Understanding this helps you predict what happens if you swap inputs: try turning a small DC motor with your hand. Often it will act like a generator and light an LED if you can connect it right.

One idea to remember

Motors and generators are built from the same basic parts — coils and magnets — but they run in opposite directions of energy flow. If you supply electricity, the device can make motion (motor). If you supply motion, it can make electricity (generator).

A simple test: turn a small motor by hand while it’s connected to a meter. If the meter shows voltage, you have turned the motor into a generator. This hands-on check connects the concept directly to what you observe.