P1.1 Energy

P1.1 Energy

1. Infrared Radiation

   • All objects emit and absorb infrared radiation
     • The hotter an object the more infrared radiation it radiates
     • Dark, matt surfaces
       • Good absorbers
       • Good emitters
     • Light, shiny surfaces
       • Poor absorbers
       • Poor emitters
       • Good reflectors

2. Kinetic Theory

   • Solids
     • Strong forces of attraction
     • Particles have little energy
     • Particles vibrate around fixed positions
       • Regular and fixed arrangement
   • Liquids
     • Weaker forces of attraction
     • Irregular arrangement
     • More energy than solids
     • Move in random directions at slower speeds
   • Gases
     • No attraction
     • No arrangement
     • Random directions at high speeds
     • Lots of energy

3. Energy Transfer by heating

   • Energy transfers
     • Conduction
       • Vibrating particles pass on kinetic energy
         • Faster in solids
           • Particles closer; collide more often
         • Metals good conductors
           • Free electrons collide with particles
     • Convection
       • Area gets hot
         • Particles move further apart
           • Area less dense
             • Lighter
               • So it rises
                 • Starts to cool
                   • Falls back down
     • Evaporation
       • Liquid turns into gas
         • Particles with most energy overcome forces of attraction and escape
         • Affects rate
           • Temperature
             • Faster if higher
           • Density
             • Faster if lower
           • Surface area
             • Faster if larger
           • Airflow
             • Faster if greater
     • Condensation
       • Gas turns into liquid
         • Particles lose kinetic energy
         • Affects rate
           • Temperature
             • Faster if lower
           • Temperature of surface
             • Faster if lower
           • Density
             • Faster if higher
           • Airflow
             • Faster if less
   • Rate at which an object transfers energy by heating depends on
     • Surface area and volume
     • Nature of the surface
     • Material
   • The bigger the temperature difference between an object and its surroundings
     • The faster the rate at which energy is transferred by heating

4. Heating and insulating buildings

   • U- Value
     • How effective an insulator it is
       • The lower the better
   • Specific heat capacity
     • Amount of energy required to change the temperature of one kilogram of the substance by one degree celsius
       • E = m x c x 0 (theta)
   • Solar panels
     • Contain water which is heated by sun, water then used to heat buildings or provide hot water