Step 1 of 6 Motors and generators
The push on a wire
Lesson 03 showed that a current makes a magnetic field. The reverse is also true: a wire carrying a current through a magnet's field feels a push, sideways to both the wire and the field. This is the motor effect, and every electric motor uses it.
Switch on and watch the rod roll. Then make it roll the other way.
Turn the cell round and turn the magnet over, then switch on. Which way does it roll?
Step 2 of 6 Motors and generators
Half a turn
Bend the wire into a rectangular loop, a coil, on an axle between two magnet poles. The current flows one way along one side of the coil and back along the other, so one side is pushed up and the other down. The coil turns.
Switch on and watch the coil. Why does it stop?
Switch off, give the coil a spin, then switch on while it's spinning.
Step 3 of 6 Motors and generators
The split ring
The fix is a copper ring cut in two, the split ring or commutator, fixed to the axle. Two carbon brushes press on it to bring the current in. Every half turn, just as the coil passes upright, the gaps swap which brush feeds which side, so the current in the coil reverses and the pushes keep turning it the same way.
Make the coil keep spinning: a motor.
With the motor running, turn the current up to 4 A or more, then reverse it.
Step 4 of 6 Motors and generators
Making electricity
In 1831 Michael Faraday turned the motor effect round. Move a magnet into a coil of wire and a current flows; pull it out and the current flows the other way; hold it still and nothing happens. A changing magnetic field makes a current. This is electromagnetic induction.
Make the meter's needle swing both ways.
Push the magnet in slowly once, and quickly once. Compare the swings.
Step 5 of 6 Motors and generators
The generator
Keep a coil turning between magnet poles and its sides keep moving up and down through the field, so a current keeps flowing, reversing every half turn. That's a generator, and it makes alternating current. Power stations, wind turbines and bike dynamos all work this way.
Turn the handle fast enough to light the lamp fully.
Look at the wave on the screen. What kind of current does a generator make?
Step 6 of 6 Motors and generators
Same machine, two jobs
A motor and a generator are the same machine. Put electricity in and it turns; turn it and electricity comes out. That's why a wind turbine is essentially a big generator turned by the wind, and why an electric car's motor can recharge its battery.
Spin the little motor's shaft by hand to light its LED.
Why do electric cars charge their battery while braking?
Quiz Motors and generators
Check what you know
Six questions, 5 points each. One answer per question.
Done Motors and generators
Lesson complete
Now you know how a current in a field makes a push, how a split ring turns that push into a spinning motor, and how turning a coil in a field makes the electricity in your sockets.
MARIFA · Nothing you do here leaves this device.