Induction and the generator
A hand-cranked torch has no battery. Turn the handle and it lights.
- A coil sits between two poles. At rest. No current.
- The coil is spun. One side moves into the page, the other out.
- A current is made in the coil. A generator.
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The rule
A generator changes motion into electrical energy. A magnet moving near a coil induces a current in it. To induce a current is to make it flow without a battery.
Electromagnetic induction. A changing field near a coil makes current. Move a magnet in or out of a coil. A meter shows a current. Hold the magnet still and the meter shows none.
Generator. Spin a coil in a field. Induction gives a current. Fleming's right-hand rule gives the direction of the current. Use the thumb, forefinger and middle finger of your right hand. Keep them at right angles. Forefinger is the field. Thumb is the motion. Middle finger is the current.
A slip ring is a whole ring. It joins one end of the coil. With slip rings, the generator gives alternating current. With a split ring, it gives direct current.
| Machine | Energy in | Energy out |
|---|---|---|
| Motor | Electrical | Motion |
| Generator | Motion | Electrical |
A turbine is a wheel turned by steam, water or wind. In a power station, turbines spin the generators.
Worked example
You turn the handle of the torch. Its coil spins in a field. The field through the coil keeps changing. Induction gives a current in the coil. The current lights the bulb. Stop turning and the light stops.