heat transfer Flashcards
(29 cards)
what are the 3 methods of heat transfer
- conduction
- convection
- radiation
what is conduction
method of heat transfer in solids- requires particles
what is convection
method of heat transfer in liquids and gases- requires particles
what is radiation
occurs in gases and vacuums- does not require particles
demonstration of conduction
place an ice cube on a metal surface and an ice cube on a wooden surface
what happens in the conduction particle and why
-the ice on the metal surface melts very quickly (conducting)
- the ice on the wooden surface melted slowly (insulating)
what are insulators
non-metals
conduction in insulators
the atoms above the heat source absorb heat energy.
this makes them vibrate more vigorously and with greater amolitude.
these vibrations pass from atom to atom, transferring heat in the form of kinetic energy
this process is slow
describe the process of conduction in metals
-the ions and free electrons above the heat source absorb energy
-the ions slowly pass on heat energy through vibrations.
-the free electrons can now move much faster than before and as they move through the metal they collide with ions, passing on kinetic energy and making the ions vibrate more
why is air a good insulator
gas particles are too far apart to influence each other, so evry little energy can be transferred by thus method
describe the process of convection
the fluid above the heat source gets heated, expands, becomes less dense and rises. the cooler fluid flows downwards to replace it. it, in turn, gets heated and the process is reapeated
which methods of heat transfer requires particles
conduction and convection
in which type of material does conduction occur
solids
what type of material are the best conductors of heat energy
metals
which particle makes metals a better conductor of heat
free (delocalised) electrons
why are liquids and gases poor conductors
their particles are spaced too far apart
in which type of material does convection occur
liquids and gases
which colour is the best emitter of infrered radiation
shiny silver/white
which colour is the best absorber of infra-red radiation
matt black
which colour is the worst absorber of infra-red radiation
shiny sliver/ white
the hotter an object the ____ infrared radiation it gives out
more
what gives out infrared radiation
anything above absolute zero
if an object is hotter than its surroundings ____________________________________________
it will emit more than its absorbs so its temoerature will fall
if an object is colder than its surroundings_______
it will absorb more than its emits so its temoerature will rise
