The hotter an object is the
more infrared radiation it
radiates in a given time.
Dark, matt surfaces are
good absorbers and good
emitters of infrared radiation.
Light, shiny surfaces are
poor absorbers and poor
emitters of infrared radiation.
Light, shiny surfaces are
good reflectors of infrared
radiation.
P1.1.2 Kinetic Theory
The kinetic particle theory explains
the properties of the different
states of matter. The particles in
solids, liquids and gases have
different amounts of energy. They
are arranged differently and move
in different ways.
Particles in a solid are close
together in a set pattern, particles in
a liquid are close together and
random and particles of a gas are
far apart and random.
The movement of particles in
different states of matters are: in
a solid, vibration about a fixed
position; in a liquid, movement
around each other; in a gas,
movement quickly in any direction.
P1.1.3 Energy Transfer By
Heating
The transfer of energy by
conduction, convection,
evaporation and
condensation involves
particles.
Heat energy can move through a
substance by conduction. Metals are
good conductors of heat but non-metals
and gases are usually poor conductors.
Poor conductors are called insulators.
The electrons in metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now charged metal
ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy
is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.
Liquids and gases are fluids and their
particles can move from place to place.
Convection occurs when particles with a lot of
heat energy in a liquid or gas move and take
the place of particles with less heat energy.
Liquids and gases expand when heated
because the particles move faster when at
higher temperatures. As a result, the particles
take up more volume because the gap
between particles widens, while the particles
themselves stay the same size. The liquid or
gas in hot areas is less dense than the liquid or
gas in cold areas, so it rises into the cold
areas. The denser cold liquid or gas falls into
the warm areas. In this way, convection
currents that transfer heat from place to place
are set up.
Evaporation and condensation
are changes of state: evaporation
involves a liquid changing to a
gas and condensation involves a
gas changing to a liquid.
The particles in a liquid have different energies. Some will have enough energy to
escape from the liquid and become a gas. The remaining particles in the liquid have a
lower average kinetic energy than before, so the liquid cools down as evaporation
happens.
The particles in a gas have different
energies. Some may not have enough
energy to remain as separate particles,
particularly if the gas is cooled down.
They come close together and bonds
form between them. Energy is released
when this happens.
The rate of condensation increases if the temperature of
the gas is decreased. The rate of evaporation increases
if the temperature of the liquid is increased. It is also
increased if the surface area of the liquid is increased or
air is moving over the surface of the liquid.
The rate at which an object transfers energy
by heating depends on surface area and
volume, the material from which the object is
made and the nature of the surface with which
the object is in contact.
The bigger the temperature difference between an object and its
surroundings, the faster the rate at which energy is transferred by heating.
Small animals like mice have a large surface area compared to their volume. They lose heat to their surroundings very quickly. Large animals like
elephants have a small surface area compared to their volume. They lose heat to their surroundings more slowly and may even have difficulty
avoiding overheating. Elephants have large ears with a large surface area compared to their volume. These allow heat to be transferred from the
elephant to its surroundings, helping to keep the animal cool. In general, similar animals have different ear sizes depending on the climate in which
they live. The arctic fox has much smaller ears than the fennec fox, which lives in the desert. The arctic fox must conserve its heat energy in the
cold climate, while the fennec fox must avoid overheating in the hot climate.
P1.1.4 Heating And Insulating Buildings
U-values measure how
effective a material is as an
insulator; the lower the U-value,
the better the material is as an
insulator.
Solar panels may contain water that is
heated by radiation from the Sun. This
water may then be used to heat buildings or
provide domestic hot water.
The specific heat capacity of a substance is the
amount of energy required to change the
temperature of one kilogram of the substance by one
degree Celsius; E=m×c×θ.
E is energy transferred in joules, m is mass in kilograms, θ is
temperature change in degrees Celsius and c is specific heat
capacity in J / kg °C.