Infra red radiation
* Infra red waves are part of the electromagnetic spectrum
* Just beyond visible red light
* Detect infra red radiation with our skin- makes us feel warm.
* All objects emitt infra red radiation
* The hotter, the more infra red radiation is emitts.
* Can travel through a vaccuum- how we get enery from the sun.
Surfaces and radiation
* Dark, matt surfaces are good absorbers of infra red radiation.
* Dark, matt surfaces are good emitters of intra red radiation.
* Light, shiney surfaces are good reflectors of infra red radiation.
States of matter
* Three states of matter- solid, liquid and gas
* Solid- particles vibrate about fixed positions so solid has fixed shape
* Liquid- particles are in contact with each other, can move at random, doesn't have fixed shape and can flow
* Gas- particles are far apart and move at random faster, doesn't have fixed shape and can flow
* Density of a gas is much less than a solid or a liquid
* Conduction occurs mainly in solids- liquids and gases are poor conductors
* One end of a solid is heated, particles at that end gain kinetic energy and vibrate more. Energy passed to particles, all energy transferred.
* Metels heated, free electrons gain K.E and move through the metal, transferring energy.
* Materials such as wool and fibreclass are good insulators
* Non-metals are poor conductors as they don't have free electrons
* Convection occurs in fluids- liquids and gases
* Convection is the circulation of fluids caused by heating it
* When fluid is heated, it expands, becomes less dense and rises. Warm fluid is replaced by cooler, denser fluids.
* Evaportation is when liquid turns into gas
* Takes place because the most energetic liquid molecules escale from the liquid's surface and enter the air. Average K.E is less, so temperature decreases- causes cooling.
* Rate of evaportation is increased by
- increasing surface area
- increasing temperature
- creating a draught of air across the liquid's surface
* Condensastion is when a gas turns into a liquid
* Takes place of cold surfaces such as windows and mirrors
* Rate of condensation is increased by
- increasing surface area
- reducing the surface temperature
Energy Transfer by Design
* The greater the temperature difference between object and surroundings, the greater the rate energy is transferred
* Rate at which energy is transferred depends on
- materials object is in contact with
- the object's shape
- the object's surface area
* Maximise rate of energy- good conductors, painted dull black, air flow is maximised
* Minimise rate of energy- good insulators, white and shiney
Specific heat capacity
* Specific heat capacity is the amount of energy required to raise the temperature of 1 kilogram of the substance by 1'C.
* Greater the S.H.C, the more energy needed for each degree temp. change
* The greater the mass of an object, the more slowly it;s temperature increases when heated.
E=m x c x temp. change
E- energy transferred, J c- specific heat capacity, J/kg 'C
m- mass, kg temp. change, 'C
Heating and insulating buildings
* U-Values tell us how much energy per second passes through difference materials. The lower the U-Value, the better the material is as an insulator.
* Can be reduced by
- fibreglass loft insualtion to reduce energy transfer by conduction
- cavity wall insulation reduces energy transfer by convection
- double glazing to reduce energy transfer by conduction