dissipation

• • energy can be transferred usefully, stored and dissipated but can never be created or destroyed
  • some energy is always dissipated during an energy transfer
• dissipation example:

  • mobile phone is system
  • using phone causes energy to be usefully transferred from chemical energy store of battery in phone
  • some energy dissipated in transfer to thermal energy store of phone
• energy transfer in closed system:

  • cold spoon dropped in insulated flask of hot soup and sealed
  • spoon and soup form closed system - flask acts as perfect thermal insulator
  • energy transferred from thermal energy store of soup to thermal energy store of spoon, cooling soup
  • no energy has left system, so net change in energy is zero
• • for a radio or set of speakers, the electrical work is transferred into useful sound waves and infrared radiation is dissipated - wasted as heat energy
• • for a tumble dryer, the electrical work is transferred into useful internal (thermal) energy which helps to dry clothes - energy is dissipated by sound waves