衢这个字粤语怎样读?:已知天空是蓝色的，请推导出“阿伏加德罗常数”?

看看这里面。据说是爱因斯坦干的：

Original by Philip Gibbs May 1997.

Why is the sky blue?
A clear cloudless day-time sky is blue because molecules in the air scatter
blue light from the sun more than they scatter red light. When we look
towards the sun at sunset, we see red and orange colours because the blue
light has been scattered out and away from the line of sight.

The white light from the sun is a mixture of all colours of the rainbow.
This was demonstrated by Isaac Newton, who used a prism to separate the
different colours and so form a spectrum. The colours of light are
distinguished by their different wavelengths. The visible part of the
spectrum ranges from red light with a wavelength of about 720 nm, to violet
with a wavelength of about 380 nm, with orange, yellow, green, blue and
indigo between. The three different types of colour receptors in the retina
of the human eye respond most strongly to red, green and blue wavelengths,
giving us our colour vision.

Tyndall Effect
The first steps towards correctly explaining the colour of the sky were
taken by John Tyndall in 1859. He discovered that when light passes through
a clear fluid holding small particles in suspension, the shorter blue
wavelengths are scattered more strongly than the red. This can be
demonstrated by shining a beam of white light through a tank of water with a
little milk or soap mixed in. From the side, the beam can be seen by the
blue light it scatters; but the light seen directly from the end is reddened
after it has passed through the tank. The scattered light can also be shown
to be polarised using a filter of polarised light, just as the sky appears a
deeper blue through polaroid sun glasses.

This is most correctly called the Tyndall effect, but it is more commonly
known to physicists as Rayleigh scattering--after Lord Rayleigh, who studied
it in more detail a few years later. He showed that the amount of light
scattered is inversely proportional to the fourth power of wavelength for
sufficiently small particles. It follows that blue light is scattered more
than red light by a factor of (700/400)^4 ≈ 10.

Dust or Molecules?
Tyndall and Rayleigh thought that the blue colour of the sky must be due to
small particles of dust and droplets of water vapour in the atmosphere.
Even today, people sometimes incorrectly say that this is the case. Later
scientists realised that if this were true, there would be more variation of
sky colour with humidity or haze conditions than was actually observed, so
they supposed correctly that the molecules of oxygen and nitrogen in the air
are sufficient to account for the scattering. The case was finally settled
by Einstein in 1911, who calculated the detailed formula for the scattering
of light from molecules; and this was found to be in agreement with
experiment. He was even able to use the calculation as a further
verification of Avogadro's number when compared with observation. The
molecules are able to scatter light because the electromagnetic field of the
light waves induces electric dipole moments in the molecules.

Why not violet?
If shorter wavelengths are scattered most strongly, then there is a puzzle
as to why the sky does not appear violet, the colour with the shortest
visible wavelength. The spectrum of light emission from the sun is not
constant at all wavelengths, and additionally is absorbed by the high
atmosphere, so there is less violet in the light. Our eyes are also less
sensitive to violet. That's part of the answer; yet a rainbow shows that
there remains a significant amount of visible light coloured indigo and
violet beyond the blue. The rest of the answer to this puzzle lies in the
way our vision works. We have three types of colour receptors, or cones, in
our retina. They are called red, blue and green because they respond most
strongly to light at those wavelengths. As they are stimulated in different
proportions, our visual system constructs the colours we see.

When we look up at the sky, the red cones respond to the small amount of
scattered red light, but also less strongly to orange and yellow
wavelengths. The green cones respond to yellow and the more strongly-
scattered green and green-blue wavelengths. The blue cones are stimulated
by colours near blue wavelengths which are very strongly scattered. If
there were no indigo and violet in the spectrum, the sky would appear blue
with a slight green tinge. However, the most strongly scattered indigo and
violet wavelengths stimulate the red cones slightly as well as the blue,
which is why these colours appear blue with an added red tinge. The net
effect is that the red and green cones are stimulated about equally by the
light from the sky, while the blue is stimulated more strongly. This
combination accounts for the pale sky blue colour. It may not be a
coincidence that our vision is adjusted to see the sky as a pure hue. We
have evolved to fit in with our environment; and the ability to separate
natural colours most clearly is probably a survival advantage.

Sunsets
When the air is clear the sunset will appear yellow, because the light from
the sun has passed a long distance through air and some of the blue light
has been scattered away. If the air is polluted with small particles,
natural or otherwise, the sunset will be more red. Sunsets over the sea may
also be orange, due to salt particles in the air, which are effective
Tyndall scatterers. The sky around the sun is seen reddened, as well as the
light coming directly from the sun. This is because all light is scattered
relatively well through small angles--but blue light is then more likely to
be scattered twice or more over the greater distances, leaving
the yellow, red and orange colours.

Blue Haze and Blue Moon
Clouds and dust haze appear white because they consist of particles larger
than the wavelengths of light, which scatter all wavelengths equally (Mie
scattering). But sometimes there might be other particles in the air that
are much smaller. Some mountainous regions are famous for their blue haze.
Aerosols of terpenes from the vegetation react with ozone in the atmosphere
to form small particles about 200 nm across, and these particles scatter the
blue light. A forest fire or volcanic eruption may occasionally fill the
atmosphere with fine particles of 500-800 nm across, being the right size to
scatter red light. This gives the opposite to the usual Tyndall effect, and
may cause the moon to have a blue tinge since the red light has been
scattered out. This is a very rare phenomenon--occurring literally once in
a blue moon.

Opalescence
The Tyndall effect is responsible for some other blue coloration's in
nature: such as blue eyes, the opalescence of some gem stones, and the
colour in the blue jay's wing. The colours can vary according to the size
of the scattering particles. When a fluid is near its critical temperature
and pressure, tiny density fluctuations are responsible for a blue
coloration known as critical opalescence. People have also copied these
natural effects by making ornamental glasses impregnated with particles, to
give the glass a blue sheen. But not all blue colouring in nature is caused
by scattering. Light under the sea is blue because water absorbs longer
wavelength of light through distances over about 20 metres. When viewed
from the beach, the sea is also blue because it reflects the sky, of
course. Some birds and butterflies get their blue colorations by
diffraction effects.

Why is the Mars sky red?
Images sent back from the Viking Mars landers in 1977 and from Pathfinder in
1997 showed a red sky seen from the Martian surface. This was due to red
iron-rich dusts thrown up in the dust storms occurring from time to time on
Mars. The colour of the Mars sky will change according to weather
conditions. It should be blue when there have been no recent storms, but it
will be darker than the earth's daytime sky because of Mars' thinner
atmosphere.

空气中颗粒的大小（考虑它对不同频率光的散射）
蓝色光波长
空气密度
平均分子量29

只想到这么多，不知道具体怎么算

挺深的 还是不是知道了