雪為什么是白色的？
[ 2006-11-20 16:18 ]
又到冬天了，漫天飛舞的雪花總能給人帶來無限的遐思。在欣賞這美妙雪景的同時,不知您有沒有想過: 雪為什么是白色的?
如果雪變成了紅色或是綠色,還能給您同樣的遐想嗎?
 One of the reasons that so many people love snow is
that it coats everything in a clean, "pure" white blanket. Snow wouldn't be snow
if it wasn't white. But why is snow white?
To understand where the whiteness comes from, we need to back up and look at
why different things have different colors in the first place. Visible light is
made up of many different frequencies of light. Our eyes detect different
frequencies as different colors. Different objects have different colors because
the atoms and molecules that make up the object have different vibration
frequencies. Basically, the electrons of the particle will vibrate a certain
amount in response to energy, depending on the frequency of the energy. In the
case of light energy, the molecules and atoms absorb a certain amount of light
energy depending on the frequency of the light, and then emit this absorbed
energy as heat.
A couple of different things can happen to the light frequencies that are not
absorbed. In some material, when a particle re-emits the photons, they continue
to pass through to the next particle. In this case, light travels all the way
through the material, so the material is clear. In most solid material, the
particles re-emit most of the unabsorbed photons out of the material, so no
light, or very little light, passes through and the object is opaque. The color
of an opaque object is just the combination of the light energy that the
object's particles did not absorb.
So, since snow is frozen water, why does it have a distinctive color? Ice is
not transparent; it's actually translucent. Snow is a whole bunch of individual
ice crystals arranged together. When a light photon enters a layer of snow, it
goes through an ice crystal on the top, which changes its direction slightly and
sends it on to a new ice crystal, which does the same thing. Basically, all the
crystals bounce the light all around so that it comes right back out of the snow
pile. It does the same thing to all the different light frequencies, so all
colors of light are bounced back out. The "color" of all the frequencies in the
visible spectrum combined in equal measure is white, so this is the color we see
in snow, while it is not the color we see in the individual ice crystals that
form snow.
vibration frequencies: 振幅
opaque：不透明的
photon：光子
（英語點津 Annabel 編輯） |
