Energy Stores and Transfers

• Energy Stores and Systems

  . A system is an object or group of objects

  . When a system changes, there are changes in the way energy is stored, e.g. a roller coaster transfers energy between gravitational and kinetic energy

  . Diagrams are a useful way to illustrate how the energy is redistributed when a system is changed

  . The Sankey diagram shows that the light bulb redistributes the electrical energy as heat and light
• Things you need to be able to calculate

  • Energy associated with a moving object
  • Energy associated with an object raised above ground level
  • Energy associated with a stretched spring
• Internal energy


  The total kinetic and potential energy of all the particles that make up a system
• Doing work on a system

  Increases the energy stored in a system
• Heating a system


  Changes the energy stored in a system by increasing the energy of particles within it
• As the energy increases


  This will either increase the temperature or produce a change of state
• Factors affecting temperature increase

  • Mass of the substance heated
  • What the substance is
  • Energy input
• Specific heat capacity


  The amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius
• What is a key point to remember about the amount of energy stored and the amount of work done?

  The amount of energy stored can also be found by the amount of work done, so you need to look at the information you are given. If you have not been given the information needed to use the elastic potential energy equation, but have been given force and distance, then use work done = force x distance
• Investigate the specific heat capacity of materials

  1. Set up the apparatus

  2. Measure the start temperature

  3. Switch on the electric heater for 5min

  4. Measure the end temperature

  5. Measure the voltage and current to find the power

  6. Repeat for different liquids

  7. Calculate the specific heat capacity

  8. Compare your results to another group's
• The energy provided by the heater is calculated as power x time. However, it could also be found using a joulemeter
• The specific heat capacity is calculated from the energy provided, the mass of the liquid and the temperature change
• If the temperature rise is too high, energy loss to the surroundings will affect the results
• Variables

  • Independent variable is the type of liquid
  • Dependent variable is the temperature
  • Control variables are the amount of liquid used and energy provided