P2

• Energy:

  • the ability to do work
  • measured in Joules (J) or kilojoules (KG)
  • It is transferred from one store to another
• Energy Stores:

  • Chemical - foods, fuels, batteries
  • Thermal - bodies with temperature
  • Kinetic - bodies that are moving
  • Gravitational potential - bodies above the ground
  • Elastic potential - bodies under tension/stretched
• Power:

  • the rate at which energy is transferred in a time period (usually in 1 second)
  • measured in Watts (W)
  • 1 Watt = 1 Joule/second
  • e.g a 60W lightbulb transfers 60J/s
• Energy units:

  • Household energy bills are calculated based upon the number of 'units' used or kWh
  • kWh = kilowatt hours
  • e.g a cooker that used 2000W is on for 30 minutes. It used 2kW in 0.5 hours. 2x0.5 = 1kWh
  • Convert W into kW = divide by 1000
  • Convert hours into minutes e.g 1hr30 = 90 minutes/60 = 1.5
• Energy conservation:

  • In a system where energy transfers occur, the amount of energy before and after remains the same
  • Energy is often dissipated to surroundings, normally in form of heat
• Reducing unwanted energy transfers (moving parts) - using lubrication (oil) can reduce friction and decrease unwanted thermal energy transfers
• Reducing unwanted energy transfers (at home) - using poor thermal conductors in homes e.g double glazing windows, loft insulation
• Poor thermal conductors usually contain air. Air is a good thermal insulator because conduction is slower in gases
• Modelling energy transfer:

  • Sankey Diagrams can be drawn to model the efficiency of energy transfer in a system
  • The size of the arrows indicates the amount of energy

  
• Energy resources:

  • Primary sources = non renewable energy →fossil fuels(oil,coal,gas)
  • Secondary sources = renewable energy → e.g solar, wind, hydroelectric, tidal/wave
• Thermal Power Station (fossil fuel/nuclear):

  1. Water heated into steam
  2. Steam turns turbine
  3. Generator spins a magnet in coil of wire inducing a current
• Reducing unwanted energy transfer - Insulation used a has low thermal conductivity, this means the rate of energy transfer is slower
• Energy dissipation - when energy stores are emptied and filled in a system, some energy is always dissipated. This reduces the useful energy available. Energy is always dissipated by heating which is not useful to us
• Nuclear Energy:

  • More efficient than fossil fuels
  • Dangerous because waste is radioactive
• Renewable Power Station:

  • Turbines are connected directly to a generator
  • No heating/burning of fuels needed
  • No greenhouse gas pollution
• Domestic Energy Supply:

  • UK power sockets transfer 230V of energy
  • This is transferred at a frequency of 50Hz
  • Domestic energy in homes is connected to the mains national grid
  • Transferred though alternating current/voltage
• Alternating Voltage:

  • Electrical energy that is constantly changing direction
  • Produced by most power stations and is used in mains electricity to our homes
  • Can be transferred over long distances and is used when lots of devices need energy
• Direct Voltage:

  • Electrical energy that always flows in one direction
  • Produced by solar panels and batteries
  • Can't be transferred efficiently over long distances
• Batteries:

  • Store of chemical energy, when a circuit is complete, current flows
  • Voltage provided changes depending on the battery (3V,6V,9V)
  • It is transferred through a direct current/voltage
• Transformers:

  • Used to transfer electrical power at high voltages from power stations (Step up transformer)
  • Used again to transfer power at lower voltages locally for domestic use (Step down transformer)
• The National Grid - Transfers energy around the country through transmission lines
• Mains Plugs:

  • Cable grip - holds wires in place so they don't lose connection
  • Fuse - contains thin wire which melts if the current gets too high
  • Live wire (brown) - carries 230V of energy in a current from mains socket to the device
  • Earth wire (green/yellow) - provides a path for current to flow from the case there is a fault
  • Neutral wire (blue) - completes the circuit, the current flows back into the socket

  
• Energy Demand - world energy demand is increasing due to a population increase and improved technology
• Reducing Energy Demand - concerns about climate change and increasing energy demand have led people to put pressure on governments for using more renewable energy sources which are sustainable