The transfer of energy by conduction, convection, evaporation and condensation involves particles
Conduction
Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles
The process continues throughout the solid, gradually the kinetic energy is passed throughout the solid- causing a rise in temperature (at the other end of the solid)
Hence an increase in heat radiating from the surface of the solid
Conduction is usually faster in denser solids, as particles are closer together
collide more frequently, passing energy between them
Materials that have larger spaces between their particles conduct energy much more slowly
these materials are insulators
or this reason, glass is a better insulator than wood
wool and fibreglass are the best insulators
in metals
Metals contain lots of free electrons
which move about at random
and hold the positive metal
ions together (and also
collide with them)
1) When a metal rod is heated at one end, the free electrons at that end gain kinetic energy and move faster
2) These electrons diffuse and collide with other free electrons and ions in the cooler parts of the metal
3) As a result they transfer kinetic energy to these electrons and ions
and energy is transferred from the hot end of the metal to the cooler end
non-metals are good insulators,
as they do not have free electrons
convection
is the circulation of a fluid (liquid or gas) caused by heating it
it takes place
only in fluids (liquids or gases)
due to circulation (convection) currents within the fluid
1) Most fluids expand when heated
2) This is because the particles move about more, taking up more space
3) Therefore the density decreases because the same mass of fluid now occupies a bigger volume
This principle explains convection currents
1) As a fluid is heated, its reduction in density means that it rises
2) This hot fluid displaces cooler fluid, or cools itself, and therefore falls due to an increase in density
3) This cooler fluid is then heated once more- and the convection current continues circulating heat energy via the fluid
Condensation
when a gas (vapour) turns into a liquid
1) When a gas cools, its particles lose kinetic energy and slow down-
while the attractive forces pull the particles closer together
2) If the temperature gets cold enough and the particles get close enough together-condensation will take place
3) And the gas becomes a liquid
examples
water vapour in the air condenses when it come into contact with cold surfaces e.g. drinks glasses
steam: (inivisible) water vapour condenses to form tiny water droplets- as they spread out into cooler air
the factors which affect it
the rate of condensation will be faster if
The temperature of the gas is lower
This would mean the average particle energy is lower- so more
particles will slow down enough to join together and form liquid droplets
the temperature of the surface the gas touches is lower
Density is higher
fewer particles will have enough energy to overcome the stronger forces this density
induces, meaning more will join together condense
airflow is less
the concentration of that particular fluid will be higher in a reduced airflow
so the rate of condensation will be higher :3
evaporation
when a liquid turns into a gas
Fun fact: particles can evaporate from a liquid at temps
lower than that liquid's boiling point
1) Evaporation is when particles escape from a liquid
if they are travelling in the right direction and have enough kinetic energy (k.e.), this will happen
2) Weak attractive forces exist between the molecules in the liquid
3) The faster molecules, which have more k.e., break away from the attraction of other molecules and escape from the liquid
4) After they leave, the liquid is cooler because the average k.e of the remaining molecules in the liquid has decreased
uses of evap's cooling effect
sweat: evaporates, cooling you down
local anaesthetic: evaporates very easily, numbing
your skin so that it becomes too cold to feel any pain
the factors which affect it
the rate of evaporation will be faster if the
Temp is higher
the average particle energy will be higher- more
particles have enough energy to escape
Density is lower
the forces
between the
particles will be
weaker, and are
thus easier to
overcome
Surface area is larger
more particles near enough to the surface to escaoe
Airflow over the liquid is greater
The lower the amount of the evaporating substance in the surrounding air, the higher the rate of evaporation
a greater airflow means the liquid is replaced more quickly, so the concentration in the air will be lower