Energy

• System

  An object or group of objects
• Energy stores


  • Magnetic
  • Internal (thermal/heat)
  • Chemical (fuels such as petrol or batteries or stored in body from food)
  • Kinetic (moving)
  • Gravitational potential energy (high up)
  • Elastic potential energy (stretched)
  • Electrostatic (charged)
• Energy transfers


  • Heating
  • Electrical (if there is a circuit and a current flows)
  • Radiation (light/sound etc.)
  • Mechanical work (if a force is present such as gravity or friction)
• Power


  The rate at which energy is transferred or the rate at which work is done
• 1 joule per second

  Equal to a power of 1 watt
• Something is more powerful

  It does the same job (i.e. amount of work) in less time or transfers more energy in the same time
• Energy is conserved, this means it cannot be created or destroyed (in a closed system)
• Energy may be stored in less useful ways or dissipated (spread out into the surroundings) - we say this is wasted
• To reduce wasted energy

  1. Reduce friction at moving parts – lubricate

  2. Reduce heat loss – insulation (good insulators have low rates of thermal conduction and hence low thermal conductivities; thicker materials will also be better insulators)
• Efficiency


  Tells us what proportion of the input energy is transferred to useful stores
• An efficient device transfers a large proportion of the input energy usefully (and vice-versa)
• Insulation required practical


  1. Wrap beakers (should be the same size and material of beaker) in different materials/layers of insulation

  2. Fill with the same volume (control variable – keep the same each time) of hot water from a kettle and put a lid on

  3. Record the start temperature (same for all – a control variable)

  4. Record the temperature every minute for 10 minutes
• The one with the smallest temperature drop in 10 minutes is the best insulator (lowest value of thermal conductivity)
• Thermal conductivity


  A measure of the rate of energy transfer by conduction – better insulators and more layers will decrease this value
• Main energy resources


  • Fossil fuels (coal, oil and gas)
  • Nuclear fuel (uranium and plutonium)
  • Bio-fuel
  • Wind
  • Hydro-electricity
  • Geothermal
  • The tides
  • The Sun
  • Water waves
• Uses of energy resources

  • Generating electricity (e.g. wind farm)
  • Transport (e.g. petrol)
  • Heating (e.g. gas central heating)
• Types of energy resources

  • Renewable - being (or can be) replenished as it is used e.g. wind, solar, tidal, hydro, biofuel
  • Non-renewable - not being (or can be) replenished as it is used e.g. coal, oil, gas (fossil fuels), nuclear
• Reliability


  If they can always produce electricity e.g. fossil fuels, nuclear, biofuels, hydro, tides (?). If they depend on external factors such as wind speed or solar intensity then they are not reliable (predictable is a related idea)
• Environmental effects

  • Burning fuels (fossil/bio/wood) produces CO2 (global warming) and SO2 (acid rain) [biofuels/wood are carbon neutral]
  • Habitats destroyed especially by tidal and hydro schemes
  • Noise/visual pollution especially wind/hydro
  • Radioactive waste only applies to nuclear (this can remain radioactive for long periods if it has a long half life and must be safely buried underground). Nuclear powerstations also run the risk of catastrophic accidents like Chernobyl