Answer 1:
Yes, the heat of an object affects the amount of
energy (heat, sunlight) that it can absorb. At
some level of energy input, an object will reach
an equilibrium temperature. At this point, the
object is giving off exactly as much energy as it
is absorbing. Beyond this point, the object's
temperature will not rise: the only energy
absorbed is exactly what is needed to maintain
this equilibrium temperature (and thus replace
the
energy that the object is loosing to the
environment). Energy input beyond this will be
not
being absorbed. Think of a hot stove burner: if
you put it on "high", it will continue to heat up
(absorb energy) until it reaches a maximum
temperature. This maximum temperature is
determined by the material that the stove burner
is made of. Some materials don't absorb much
energy and don't heat up much; others absorb a
lot
of energy and heat up quite a bit. Once the stove
burner reaches its equilibrium temperature, it
will not heat up any more, no matter how much
energy you add. So a cold stove burner will
absorb
a lot of energy but a hot stove burner will
absorb
much less because it's closer to its equilibrium
temperature. At its equilibrium temperature, the
stove burner is giving off exactly as much energy
as it is absorbing, so to maintain this
equilibrium temperature, it does absorb energy,
but not as much as at lower temperatures. If the
stove burner was perfectly insulated, it would
not
absorb any energy at all, because it wouldn't be
loosing energy to the environment.
It's
impossible
to perfectly insulate anything, and for a stove
burner, the whole point is to transfer the heat
to
a cooking pot, so you would never want to
insulate
it anyway. But a solar water heater cell you
would
want to insulate, because you want to transfer
the
heat of sunlight to water running through the
cell
and not to the environment. Like a stove, solar
water heater cells will absorb the energy in
sunlight until they reach an equilibrium
temperature, but this temperature is not fixed.
Why? Because the solar water heater cell still
looses some energy to the environment, and this
amount of energy is determined by temperature
difference between the solar water cell and the
air outside it. So solar water heater cells can
reach some characteristic temperature ABOVE THEIR
SURROUNDINGS, and then will not heat up any more.
This is their equilibrium temperature. If the
maximum temperature increase of a solar water
cell
is 100 degrees Fahrenheit, and the outside
temperature is 40 degrees Fahrenheit, then the
inside of the solar water cell will reach 140 F
at
its equilibrium temperature and will not heat up
any more, no matter how much sunlight is hitting
it. If the outside temperature is 100 F, then the
inside temperature of the SAME solar water cell
will reach 200 F.
So solar water cells work best
in sunny, warm environments, not just sunny
environments.
And yes, the equilibrium
temperature of an object is partly determined by
its color. Think of two cars sitting in the sun
with their windows closed. If one car has black
paint and the other car has white paint, the
inside of the black car will heat up faster,
since
black colors absorb the most sunlight and white
colors absorb the least, AND the equilibrium
temperature inside the black car will actually be
higher than the equilibrium temperature inside
the
white car. Why do black colors absorb the most
sunlight? When it comes to color, light is either
being reflected or absorbed. Black things look
black because they reflect almost 0% of visible
light, which means they absorb almost all of the
sunlight that hits them. White things look white
because they reflect almost 100% of visible
light,
so they absorb very little sunlight that hits
them. |