Energy transfer

• Infra red radiation is heat energy
• Heat energy can be measured using a termometer and temperature is measured in units called *c
• Heat always transfers from a hot place to a cooler place
• The infra red radiation transfers to the surroundings
• This increases the temperature around the cup

Factors that affect the rate things cool down:

• room temperature
• starting temperature
• touch
• material
• where its placed
• amount of liquid
• colour

• All objects emit (give out) and absorb (take in) infrared radiation.
• The hotter the object the more infra red radiation is given out over time

Light and shiney surfaces:

• good reflector
• poor absorber
• poor emmiter

Dark matt surface:

• good absorber
• good ammiter

Solid:

• particles in order
• fixed shape
• fixed volume
• high density

Liquid:

• particles random
• 50% full/50% touching
• fixed volume
• high density

Gas:

• particles random lots of pace
• no fixed shape
• low volume and density

Conduction is all about when heat is transferred through a solid. The heat is passed on by vibrations in the molecules. These vibrations get bigger when solidhas more energy (i.e. when it is being heated). Metals are better conductors than non-metals. This is because the heat it carried by free electrons that can carry the energy around the metal and give it to other electrons and ions.

• good conductors are metals e.g. copper
• poor conductors are non-metals e.g. plastic, wood
• poor conductors are called insulators

Which metal is the best conductor?

• copper - more free electrons - reactive
• aluminum
• brass
• steel- least reactive

Convection is all about when gases or liquid("fluid") moves and carries heat with it. When fluid is heated it expands. this means that it will become less dense than the colder fluid around it. Because of this the warmer fluid will try to "float" over the colder fluid, and this is why warm air rises. This is called convection current. This is how the heat reaches us from the radiator in this room.

In conduction the heat was passed on by vibrations in a solid.

In convection the heat is passed on by the fluids expanding, rising and taking heat with it

• Radiation-colour
• Conduction-solid
• Convection-liquids and gases

• Causes cooling e.g nail varnish, sweating
• energy is transferred in evapouration
• particles gain energy to change state

Liquid to gas

• Causes heating e.g. shower window, bus window
• energy is transferred in condensation
• particles lose energy to change state

Gas to liquid

Conduction-

• solid-metal-good conductor
• transfers heat
• non-metal-poor conductor
• insulator

Convection-

• liquid/gas-particles moving-convection current

Radiation-

• silver-poor emitter-keep warm
• black-good emitter-transfers heat-cools

Double glazing

• How does does it work? glass and trapped air
• Method of transfer: conduction

Draught excluder

• How does it work? blocks air gaps
• Method of transfer: convection

Loft insulation

• how does it work? fibre glass and trapped air
• Method of transfer: conduction

Cavity wall insulation

• How does it work? foam/polystene and trapped air
• Method of transfer: conduction  

If loft insulation cost £800 and saves £160 per year on the fuel bill. How long is the payback time?

Payback time= 180/160 =5 years

Payback time=Cost/Saving

• U values measure how effective a material is as an insulator
• The lower the U value, the better it is as an insulator

type of glass-U value

magiglass      2.9

supaglass      1.6

wondaglass   1.9

optoglass      2.6

Which type of glass would you choose in your new double glazing? and why? supaglass because it has the lowest U value so it is the best insulator.

SCH:capacity of an object to take in heat

Always a calculation question

E.g. A piece of iron mass 0.05kg is heated until its temperature rises from 21*c to 38*c. How much energy has it absorbed? The SHC of iron is 460j/kg*c.

E=m x c x o

E= 0.05 x 460 x 17 = 390J