Answer 1:
When light hits an object, a few things can
happen. Light can partially or wholly reflect,
transmit, or absorb. The difference between
transmit and absorb is that in transmission, light
passes through and is not changed when it comes
out the other side of the object, whereas
absorption is what gives objects the color we
see. This means objects absorb some light and
reflect the colors we see, or said another way,
the colors not absorbed are what we see.
Your question is related to transmission. Light
has wavelike character. Green light has a
wavelength of 510 nm (nanometers), and orange is
about 590 nm. The speed at which a particular
wavelength (color) of light transmits through an
object will depend on the nature of the atoms in
the object. To explain this, we need to invoke
some physics and chemistry. Atoms have electrons.
If we imagine the electrons as attached to the
atoms with springs, they have the ability to
vibrate with a frequency unique to the system.
This means that for different atoms and different
arrangements of atoms, there will be a different
natural frequency for the electrons to vibrate.
When light with the same frequency hits the
material, the electrons will vibrate in resonance,
and the vibration leads to heat generation. In
this case where the light and material have the
same frequency, the light has been converted to
heat energy in the material, meaning light of the
frequency that was absorbed will not be
transmitted or reflected. On the other hand,
transmission and reflection occur when the
frequency of light does not match the frequency of
the normal vibration of the electrons. In these
cases, light hitting the material will lead to
vibrations in the electrons, but these vibrations
will be brief and light will be reemitted on the
same side the light entered (reflection) or
reemitted on the opposite side (transmission).
Light in a vacuum travels at about 300,000,000
meters per second, which we call c, the speed
of light. When light hits a material, if the
frequency of the light does not match the
frequency of the material, the light will
propagate in the empty space between the atoms at
speed c. However, it will eventually interact with
an atom in its path, and the wave will set some
electrons into vibrational motion, thereby losing
some energy. Now the wave is not operating at the
original frequency, and as discussed earlier, will
be reemitted because the frequency of the wave and
the vibrations in the material are not the same.
Additionally, this will also slow the speed at
which the light is traveling. To answer your
question about green vs. orange, it depends on how
the atoms are arranged in the material, but can be
easily manipulated by utilizing concepts such as
polarization. One interesting example is of
PLZT flash goggles, whereby the light
transmitted is controlled by applying a voltage
and tuning the polarization. This manipulation is
possible due to the nature of light, more
accurately referred to as a type of
electromagnetic radiation, where the complex
electronic and magnetic effects can be
manipulated to create technologies such as the
PLZT flash goggles.
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Answer 2:
The maximum speed of light is
~3.0x108 m/s in a vacuum (completely
empty space). Its speed slows when light passes
through a denser medium. The ratio between the
speed of light in a medium (v) and in
vacuum (c) is called the refractive index
(n), where n = c/v. Thus the refractive
index of vacuum is 1.0 and all other media is
greater than 1.0 – for example, air is 1.0003,
water is 1.33, most glass is ~1.5 and lead is 2.6.
Denser structures lead to higher refractive
indexes: diamond (carbon) has a refractive index
of 2.42 but silicon and germanium, which have a
similar structure but are denser, have 3.48 and
4.05, respectively.
Regardless of color, all light has the same
speed so it should slow down at the same rate
(called refraction) when it enters the medium.
However, the refractive index of a material can
also depend on the wavelength (color) of the
light. Most materials have very similar refractive
indexes for visible light, so we don’t notice any
color splitting as light passes through glass or
plastic. Glass prisms are designed to have
different refractive indexes at different
wavelengths in order to split light into colored
bands (called dispersion). For example, violet
light might experience n=1.53 in a prism, while
red light experiences n=1.51 – this small
difference in speed as the light passes through
the prism allows the colors become displaced in
space to form a rainbow.
For more information, check out these sites:
refraction
dispersion
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