4. Energy Resources and Energy Transfers

• Energy


  Can be transferred between different stores including chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic and nuclear as a result of an event or process
• Ways energy can be transferred


  • Mechanically
  • Electrically
  • By heating
  • By radiation
• Energy is always conserved. The total energy before is equal to the total energy after
• Efficiency


  The ratio of the useful energy output to the total energy supplied, often expressed as a percentage
• Sankey diagrams can be used to represent the transfer of input energy into useful energy and wasted energy
• Conduction


  • Thermal energy in solids and liquids can be transferred by the vibration of particles
  • Non-metals are usually poor conductors known as thermal insulators
  • Metals are usually good conductors, the free electrons collide with ions and transfer heat energy from hot parts to cooler parts
• Convection


  • Thermal energy in fluids (liquids and gases) can be transferred when molecules in a fluid move from an area of high to low thermal energy
  • When part of a fluid is heated, it expands, becomes less dense and rises up to less dense areas in the fluid
• Radiation


  • Thermal energy is also transferred by infrared radiation which does not require a medium
  • 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
  • The higher the temperature and the greater the surface area of a body the more infrared radiation emitted
• Work


  Done when a force moves something through a distance (whenever energy changes forms)
• Power


  The rate at which energy is transferred or the rate at which work is done
• Renewable energy sources


  • Wind
  • Water (hydroelectricity, waves, tides)
  • Geothermal
  • Solar (heating systems and cells)
• Renewable energy


  • Can be replenished as quickly as it is used
  • Potentially infinite energy supply
  • More costly and less reliable
• Non-renewable energy sources


  • Fossil fuels (coal, oil, gas)
  • Nuclear power
• Fossil fuels


  • Cheaper than most renewable sources but harmful for the environment because they release greenhouse gases which cause global warming
• Nuclear power


  • A small amount of radioactive material produces a lot of energy, but they produce highly toxic nuclear waste which needs to be safely stored underground for many years
• Energy transfers in electricity generation

  • Chemical energy in chemical bonds
  • Nuclear energy in atomic nuclei
  • Light energy from the sun
  • Heat energy from the Earth's core
  • Kinetic energy from the moving wind
  • Kinetic energy of the moving waves or gravitational potential energy of water stored high up