Physics

• Conduction


  Heat energy is transferred from one end of the material to the other
• Conduction

  • Normally associated with solids
  • Metals are good conductors of heat
  • Glass and plastic are poor conductors
  • Anything that is a poor conductor is a good insulator
• Good conductors


  • Metals
• Poor conductors


  • Glass
  • Plastic
• If you hold a metal rod in a flame


  The end you hold will eventually get hot
• Conduction occurs in solids only
• Conduction in solids


  1. Particles vibrate around a fixed position

  2. Vibrations in neighbouring particles

  3. Increased space between particles

  4. Material expands
• Metals


  • Better conductors of heat
  • Have free electrons (mobile electrons)
  • Can carry vibrations much faster through the material
• Convection


  When a fluid (liquid or gas) is heated it becomes less dense. Less dense fluids float above more dense fluids.
• Convection


  1. Hot, less dense air rises above cold, more dense air

  2. Heated section of liquid or gas increases in volume and decreases in density

  3. Less dense liquid rises and colder more dense liquid sinks and takes its place

  4. This process continues until all of the liquid is heated

  5. Forms a convection current
• When a section of liquid or gas is heated, the molecules gain energy and move more vigorously
• Calculating costs Formula


  Units x Cost per unit
• Formula for units used


  Power x Time
• Sankey Diagrams


  Energy input = Energy Output e.g. 50j = 45j + 5j
• Sankey Diagrams


  • Useful energy is straight on
  • Wasted energy is curved downwards/upwards
  • Width of arrows are proportional to the amount of energy
• Efficiency formula


  Useful energy out transfer divided by total energy input x 100
• Energy efficiency


  A measure of how much useful energy comes out of a device, measured in %
• Calculating energy efficiency


  USEFUL energy out (or power) transfer / TOTAL energy (or power) input × 100
• Effects of power stations on the environment

  • Waste products of generating electricity using fossil fuel (coal, oil, gas)
  • Waste products of generating electricity using nuclear power stations
• Carbon dioxide (CO₂) leads to global warming/greenhouse effect
• Fossil fuels are wasted
• Efficiency


  A measure of how good something is at converting its input energy into a useful output energy
• Efficient method of electricity generation

  • Little energy loss (wasted energy)
• Fossil fuel (coal, oil, gas) and nuclear power stations

  • Very reliable
  • Especially comparing them to other methods of electricity generation (such as renewable energy sources) that can be affected by weather
• Electricity in the UK is generated in a variety of ways
• Most of our electricity is produced by burning fossil fuels, mainly gas and coal
• When deciding which type of power station to build, it is important to consider the environmental problems they cause
• Statements about different power stations

  • Burning fossil fuels adds to climate change
  • Nuclear power stations emit lots of carbon dioxide when used
  • Tidal barrages damage marine habitats
  • Waste from gas power stations is radioactive
  • Wind power causes acid rain
• If you place two identical resistances in parallel


  You reduce the overall resistance of the circuit
• To calculate the combined resistances in parallel

  Use the formula: 1/Rtotal = 1/R1 + 1/R2
• Voltage


  Current x Resistance
• Using less energy


  Reduces the amount of greenhouse gases and other harmful pollutants that are released into the atmosphere
• The three states of matter

  • Solid
  • Liquid
  • Gas
• Units


  • Density g/cm3
  • Mass: g/kg
  • Volume: cm3
• Convection


  In terms of molecular behaviour and variations in volume and density
• Solids


  • Fixed volume and fixed density
• Liquids and gases (fluids)

  • Can change their volume and therefore their density
• Heating a liquid or gas

  1. Gain kinetic energy

  2. Move around more

  3. Expand

  4. Increase volume

  5. Decrease density

  6. Rise away from heat source

  7. Cool down

  8. Lose energy

  9. Become more dense

  10. Sink
• Radiation is the final type of heat transfer
• Radiation does not need any matter (particles) to travel because it is a (infrared) wave