Unit 6 · Lesson 6.1.3
Generating Electricity
Describe how an AC generator produces an alternating current, and explain how power stations use turbines and generators to produce electricity from a range of energy resources.
The AC Generator
1
A coil of wire is rotated between the poles of a magnet, so the coil continually cuts the magnetic field lines.
2
As the coil rotates, the induced potential difference changes direction every half turn, producing an alternating current.
3
Slip rings and brushes carry the induced current from the rotating coil into the external circuit without twisting the wires.
4
The output potential difference rises and falls in a smooth wave pattern as the coil continues to rotate.
The Power Station Chain
Heat source
- Burning fossil fuels, nuclear fission or another heat source turns water into high-pressure steam.
Turbine
- The steam, flowing water or wind spins a turbine, transferring kinetic energy to its rotating shaft.
Generator
- The turbine rotates the generator's coil or magnet, which induces a potential difference by the generator effect.
Renewable sources
- Wind, hydroelectric and tidal schemes use the energy of moving air or water to turn turbines without burning fuel.
Energy Resources
Energy Resources
Coal and gas
- Burning fossil fuels releases chemical energy as thermal energy, but produces carbon dioxide and pollutants.
Nuclear
- Nuclear fission releases thermal energy to make steam, but produces radioactive waste that must be stored safely.
Hydroelectric
- Water stored at height has gravitational potential energy, which becomes kinetic energy as it flows through a turbine.
Wind
- Moving air transfers kinetic energy to the turbine, and the output depends on the wind speed.
| Resource | Energy transfer chain | Notes |
|---|---|---|
| Coal | Chemical → thermal → kinetic → electrical | Burning releases CO₂ and pollutants |
| Nuclear | Nuclear → thermal → kinetic → electrical | Produces radioactive waste |
| Hydroelectric | Gravitational potential → kinetic → electrical | Needs suitable sites such as dams |
| Wind | Kinetic → electrical | Output depends on wind speed |
Exam Checklist & Tips
6.1.3 – Key Points for the Exam
- Alternating current: A current that repeatedly changes direction.
- Slip ring: A ring that makes electrical contact with a rotating coil while allowing it to turn.
- Turbine: A machine with blades that is spun by steam, water or wind to drive a generator.
- Generator: A device that converts kinetic energy into electrical energy using the generator effect.
- Renewable energy resource: An energy source that is replenished naturally and will not run out.
Common Mistakes
- Saying a generator creates energy; it transfers energy from kinetic to electrical.
- Forgetting that the turbine, not the generator, is driven directly by the steam or water.
- Describing the output of a simple AC generator as direct current; its direction alternates every half turn.
- Ignoring that wind and hydroelectric output depends on weather and water levels.