Physics P2

• what does thermal. conductivity of a metal mean?

  tells you how quickly energy is transmitted through it by thermal conduction.
• how can you test the thermal conductivity of metals?

  Each rod must have the same diameter and length, and the same temperature difference between its ends. One end of each rod is covered in wax and the other ends are heated equally. The faster the wax melts, the higher the thermal

  conductivity of the metal.
• factors that affect the rate of heat loss from a building include:

  1 the thickness of its walls and roof

  2 the thermal conductivity of its walls and roof.
• What does lower thermal conductivity equal?

  lower thermal conductivity = lower rate of heat loss
• how can the thermal conductivity of walls be reduced by?

  by using thermal insulators.
• what is a thermal insulator?

  a material which has a low thermal conductivity.
• is the rate of energy transfer through an insulator high or low?

  low
• The energy transfer per second through a material depends on:


  1 the material's thermal conductivity

  2 the temperature difference between the two sides of the material

  3 the thickness of the material.
• What is a convection current?

  the way that heat is transferred throughout a fluid
• What is radiation?


  The transfer of energy by electromagnetic waves
• what is a conduction current?

  amount of current or charges that flow through the conduction surface within a time
• what type of heat transfer does loft insulation stop?

  convection
• how does loft insulation stop heat transfer?


  Heat rises through the house. Loft insulation contains trapped air which forms an insulating layer between the loft and the rest of the house
• what type of heat transfer does foil behind radiators stop?

  radiation
• how does foil behind radiators stop radiation?


  foil reflects the radiation away and so reduces rate of energy transfer by radiation
• what type of heat transfer does double glazing stop?

  convection + conduction
• how does double glazing stop conduction + convection?

  2 glass ones with dry air or a vacuum between the panes. Thicker glass and lower thermal conductivity is, the slower the rate of conduction
• what type of heat transfer does draught excluders stop?

  conduction
• how does draught excluders stop conduction?

  blocks air coming through two exposed areas of the house
• what type of heat transfer does cavity wall insulation stop?

  conduction
• how does cavity wall insulation stop conduction?

  Insulation is pumped into the cavity. Traps air into small pockets and reduce energy conduction
• When a substance is heated or cooled the temperature

  change depends on:

  • the substance's mass

  • the type of material

  • how much energy is transferred to it.
• what is specific heat capacity?

  The amount of energy required to increase the temperature of 1kg of a substance by 1C
• change in thermal energy equation

  Mass x specific heat capacity x temperature change
• what is the electromagnetic spectrum?


  The complete range of all types of radiation that has both electric and magnetic fields and travels in waves.
• do all objects emit and absorb infrared radiation?

  yes
• The higher the temperature of an object means...


  the more infrared radiation it emits in a given time.
• A good absorber of infrared radiation is also a...

  good emitter.
• For an object at a constant temperature:


  • infrared radiation emitted = infrared radiation absorbed

  • infrared radiation is emitted across a continuous range of wavelengths.
• what happens when an object absorbs more infrared radiation than it emits?

  its temperature will increase
• what is a black body


  a theoretical object that absorbs 100% of the radiation that falls on it.
• what would a perfect black body do?

  it would not reflect or transmit any radiation, and would also be a perfect emitter of radiation.
• what are some of the factors that effect the earths temperature?

  the rate at which visible light and infrared radiation are reflected, absorbed, and emitted by the Earth's atmosphere and surface.
• what do green house gases do?


  absorb infrared radiation emitted by the surface of the Earth and prevent it escaping into space.
• what do greenhouse gases do after absorbing infrared radiation?


  re-emit the infrared radiation back towards the surface of the Earth, increasing the Earth's temperature.
• what do greenhouse gases in the earths atmosphere include?

  include water vapour, methane, and carbon dioxide.
• what human activities increase greenhouse gases?


  burning fossil fuels, deforestation, and livestock farming