condensed physics

• Energy stores


  Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear
• Energy transfers:


  Mechanically, electrically, heating, radiation
• System


  change = energy transfer

  closed = matter + energy can't enter or leave

  net change, energy = 0
• Heating


  kettle e.g. heater to water
• Doing work


  when current flows or a force

  car brakes e.g. friction between brakes and wheels
• elastic potential energy


  1/2 x spring constant x extension^2
• kinetic energy


  1/2 x mass x speed^2
• gravitional potential energy


  mass x gravitational field strength x height
• Specific heat capacity definition

  the energy required to raise the temperature of one gram of a substance by one degree Celsius
• specific heat capacity equation

  Change in thermal energy = mass x specific heat capacity x temperature change
• Energy can:


  store, dissipate, transfer
• Energy can't:


  be created or destroyed
• power, energy, time


  P = E/t
• power, work done, time

  P=W/t
• Conduction


  vibrating particles transfer energy to neighbours

  heating

  more collisions = more transfer

  hot - cold

  usually in solids

  thermal conductivity = how quick
• Convection


  particles move to colder regions

  liquids + gases

  less dense, hot air on top of more dense, cold air

  convection current created
• Radiators


  radiator - air

  air = warmer, less dense

  cold air replaces warm air

  warm air cools and then sinks

  convection current due to flow of air
• Lubricants


  reduce friction between two objects

  easier flow,

  reduces dissipation
• Insulation types


  cavity walls

  air gap reduces conduction

  foam reduces convection

  Double-glazed windows

  air gap prevents conduction

  Draught Excluders

  reduce convection
• Effeciency


  Useful energy output / total energy input
• Non-renewable energies:


  coal, oil, natural gas
• Renewable energies:


  solar, wind, waves, hydro-electric, bio-fuel, tides + geothermal
• Current and resistance relationship

  If resistance increases

  current decreases
• Charge, current, time


  Q=It
• Ohmic Conductor


  constant resistance
• I-V characteristics


  Ohmic conductor- directly proportional

  Filament Lamp - is resistance increase, current decreases

  Diode - current is in one direction as resistance increase
• Light Dependent Resistor


  bright light - resistance decrease

  dark - resistance increase
• Thermistor Resistor


  hot, resistance decreases

  cold, resistance increases
• Series circuit


  p.d adds up

  Current = the same

  resistance adds up
• parrallel circuit


  p.d. = the same

  current = shared

  if you add a resistor, resistance decreases
• Mains Supply


  AC- alternating current

  alternating current + potential difference

  230 V

  50 Hz
• Battery Supply


  DC- direct current

  same direction + resistance
• Live Wire


  Brown

  alternating potential difference
• Neutral Wire


  Blue

  completes circuit

  0 V
• Earth Wire


  yellow + green

  stops it from being live

  no current usually

  0 V
• Electric Shock


  the bodies p.d is 0 V

  large p.d + current flows

  decrease in resistance, increase in current (fire causer)
• Energy, power,time


  E = P x T
• Energy, charge, potential difference

  E = QV
• Power, current, potential difference

  P=IV
• Power, current, resistance


  Power = current^2 x resistance