P14: Energy Transfer by Heating Flashcards
What is the role of free electrons?
> When a metal is heated, the FE in the heated part gain kinetic energy, and move faster.
> These FEs diffuse and collide with other FE and ions in the cooler parts of the metal.
> As a result, kinetic energy is transferred into these new FE’s.
What are the best conductors of energy?
Metals (contain free electrons)
What are the best insulators?
Wool and Fibreglass (insulating air pockets)
Convection
Circulation of a liquid or gas caused by increasing its thermal energy.
Convection only takes place in…
… fluids because of circulation within a fluid.
Why does convection occur when a substance is heated?
Heating a fluid makes it less dense, which will cause it to rise. This pushes cooler fluid to the bottom where it is also heated, etc etc.
Evaporation
When particles escape the surface of the fluid and entre the air.
How does evaporation cool a substance?
> Relatively weak forces of electrostatic attraction exist between the particles of a liquid.
> The faster particles with more kinetic energy break away from the particles at the surface and escape through evaporation.
> This leaves the liquid cooler because the average kinetic energy of each particle has decreased.
The higher the temperature of an object…
… the more infrared radiation it emits at a given time.
What is infrared radiation?
Energy transfer by electromagnetic waves.
Do all human bodies emit or absorb infrared radiation?
Both
What are the best surfaces for absorbing radiation?
Dark, Matt Surfaces
What are the best surfaces for reflecting infrared radiation?
Light, Shiny Surfaces.
Why do dark matt surface absorb Infrared radiation Better?
The surface has lots of cavities.
What are the best surfaces for emitting infrared radiation?
Dark, Matt Surfaces.
