Metals are good conductors;
non-metals and gases aren't
In metals, the electrons can leave their
atoms and leave ions behind. The ions
vibrate more because the thermal energy
excites them, so they give off more kinetic
energy. This kinetic energy is carried by the
electrons, colliding with other particles as
it travels. The vibrations spread
throughout the metal and thus the heat
has been transferred.
Insulators are substances that stop heat
from passing through. Air is a good example
of this.
Convection
How heat is transferred in fluids
(i.e: liquids and gases)
Travel in convection currents
STEP 1: Particles are heated, so they expand. The
gaps between the particles expand so the particles
become less dense and rise up.
STEP 2: These heated particles take the place of the colder particles
above, so the colder particles, which are more dense, sink below to
the heat source.
STEP 3: The warmer particles above cool down and sink again,
with the previously colder particles now warmed up again. The
cycle continues and makes a convection current.
Radiation
How heat is transferred without particles and
instead through waves
Thermal energy is transferred by
radiation through infrared waves. The
hotter something is, the more infrared
radiation it emits.
Radiation can even pass through the vacuum of space, which is why
vacuum flasks are useful. The vacuums in vacuum flasks have no
particles, which prevents heat from leaving it via conduction or
convection. The silvery surface on it however also prevent heat loss
via radiation.
Black, matt surfaces are good absorbers and emitters of radiation.; shiny, silvery
surfaces are not (because they are good reflectors)
Sankey Diagrams
Efficiency
Useful Energy Out / Total Energy In
Width of arrows = how many joules
The width of the leaving arrows must add up
to the total square length.