Edexcel Physics IGCSE Topic 4: Energy Resources and Energy Transfers - Summary Notes

Energy can be transferred between different stores:
- Chemical
- Kinetic
- Gravitational
- Elastic
- Thermal
- Magnetic
- Electrostatic
- Nuclear
Energy can be transferred in various ways:
- Mechanically (e.g., gravity accelerating an object gives it kinetic energy).
- Electrically (e.g., current through a lamp emits light and heat).
- By heating (e.g., a fire heating an object).
- By radiation (e.g., vibrations causing sound waves or an object emitting electromagnetic radiation).
Energy is always conserved. The total energy before equals the total energy after.

Efficiency is the ratio of useful energy output to the total energy supplied, often expressed as a percentage.
Formula: $\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%%$

Sankey diagrams represent the transfer of input energy into useful and wasted energy. For example, a Sankey diagram for a lamp shows input electrical energy being converted into useful light energy and wasted heat energy.

Thermal energy in solids and liquids can be transferred by the vibration of particles (conduction).
Non-metals are poor conductors (thermal insulators).
When a substance is heated, molecules vibrate more, hitting adjacent molecules and transferring heat energy from hot to cooler parts.
Insulators reduce unwanted energy transfer (e.g., in homes).
Metals are good conductors because electrons can move freely among positively charged ions.
When a metal is heated, ions and electrons vibrate more. Free electrons collide with ions, transferring heat energy from hot to cooler parts.

Thermal energy in fluids (liquids and gases) can be transferred by convection.
Convection occurs when molecules in a fluid move from an area of high to low thermal energy.
Preventing fluid circulation can reduce unwanted energy transfer by convection.
When part of a fluid is heated, it expands, becomes less dense, and rises. Denser, colder fluid falls to take its place.
Examples of convection include water boilers and hot air balloons.

Thermal energy is transferred by infrared radiation, which does not require a medium.
Infrared radiation is part of the electromagnetic spectrum.
Black bodies with a dull texture are the best absorbers and emitters of radiation.
White bodies with a shiny texture are the best reflectors of radiation.
Shiny surfaces can reduce unwanted energy transfer (e.g., on vacuum flasks).
The higher the temperature and greater the surface area of a body, the more infrared radiation is emitted.

Work is done when a force moves something through a distance (whenever energy changes forms).
The work done is equal to the energy transferred.
Formula: $\text{work done} = \text{force} \times \text{distance}$ , or $W = Fd$
The conservation of energy links gravitational potential energy, kinetic energy, and work.
When a ball is dropped, gravity does work on it, and its gravitational potential energy becomes kinetic energy.
Kinetic energy formula: $E_k = \frac{1}{2}mv^2$
Gravitational potential energy formula: $E_p = mgh$
Power is the rate at which energy is transferred or the rate at which work is done.
Formula: $P = \frac{W}{t}$

Renewable energy: energy that can be replenished as quickly as it is used.
- Examples: wind, water (hydroelectricity, waves, tides), geothermal, solar (heating systems and cells).
- Advantages: potentially infinite energy supply.
- Disadvantages: costly and less reliable (e.g., intermittent wind, weather-dependent solar energy).
Non-renewable energy: used more for large-scale energy supplies but will eventually run out.
- Examples: fossil fuels (coal, oil, gas), nuclear power.
  - Fossil fuels: cheaper but harmful to the environment due to greenhouse gas emissions causing global warming.
  - Nuclear power: produces a lot of energy from a small amount of radioactive material but generates highly toxic nuclear waste requiring safe, long-term underground storage.

In burning fossil fuels: chemical energy in chemical bonds.
In nuclear reactors: nuclear energy in atomic nuclei.
In a solar cell: light energy from the sun.
In geothermal energy: heat energy from the Earth’s core.
In wind energy: kinetic energy from the moving wind.
In HEP: kinetic energy of moving waves or GPE of water stored high up is transferred into kinetic energy in a turning turbine, then into electrical energy.