Energy
Energy forms and transfers, thermal transfer, conservation, power, power stations and the grid.
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Before you begin
Energy is never used up; it is transferred from one form to others. This topic names the energy forms, follows the energy through a device, calculates power, and traces electricity from a power station to your home.
Be comfortable with: dividing one quantity by another, and using joules and seconds.
Learning goals
- Forms of energy
- Direction of thermal transfer
- Conservation of energy
- Power
- Fossil-fuel electricity generation
- High-voltage transmission
- Step-up and step-down transformers
Syllabus statements covered
- show an understanding that electrical energy, kinetic energy, light energy, potential energy (chemical, elastic and gravitational), sound energy and thermal energy are examples of different forms of energy
- show an understanding that thermal energy is transferred from a region of higher temperature to a region of lower temperature until both regions reach the same temperature
- state the principle of conservation of energy and apply the principle to solve problems
- recall and apply the relationship power = energy / time taken to solve problems
- describe the generation of electricity with reference to the energy conversions that take place in fossil fuel power stations
- explain why electricity is transmitted from power stations through a grid of high voltage transmission lines
- describe the use of step-up and step-down transformers in transmission of electricity and in electrical appliances (the term alternating current is not required)
Lessons
Work through them in order.
- Energy forms and transferName the energy forms before and after a change, and predict which way thermal energy transfers.
- Conservation and powerAccount for every energy output with conservation of energy, and calculate power from energy and time.
- Generation and the gridTrace energy through a fossil-fuel power station and explain why the grid steps voltage up and down.
Practise and check
Or choose
Topic reference
Quick reference
| Quantity | How to find it | Unit |
|---|---|---|
| power | energy transferred ÷ time | watt (W) |
| energy transferred otherwise | energy input − useful energy output | joule (J) |
Core knowledge to remember
- The energy forms are electrical, kinetic, light, sound and thermal energy, and chemical, elastic and gravitational potential energy.
- Energy cannot be created or destroyed, only transferred. The total output equals the input.
- Energy is transferred thermally from a hotter object to a cooler one until they reach the same temperature.
- In a power station: fuel heats water, steam turns a turbine, and the turbine turns a generator.
- The grid uses a high voltage for long-distance transmission, because the smaller current wastes less energy heating the cables.
Common mistakes
- Saying energy is used up, or leaving an output such as sound or thermal energy out of an energy account.
- Multiplying energy by time instead of dividing to find power.
- Saying cold flows into a cooling object.
- Saying transformers produce electricity, or that high voltage makes it travel faster.