Making Waves
A vibrating source creates waves.
A vibrating
electrically
charged rod will
create a set of
electromagnetic
waves.
Making Electromagnetic Waves
Actually, any device
that runs on alternating
current can generate
an electromagnetic
wave.
As the electrons in this antenna move
back and forth, they generate ripples in
the electric and magnetic fields.
Electromagnetic Waves
All electromagnetic waves move through
space at the speed of light.
In a vacuum that is 3.0 x 108 m/s.
Electromagnetic Spectrum
Velocity = Frequency x Wavelength
Frequency and wavelength are inversely
proportional to each other.
If an E-M wave's frequency increases,
its wavelength must decrease by the
same amount.
Electromagnetic Spectrum
E-M waves are classified and ranked
according to their frequency and wavelength.
Selectivity in Nature
Substances can either reflect, absorb, or
transmit E-M waves that fall upon them.
In this example, the glass is opaque to infrared
and ultraviolet light, but for visible light it is
transparent.
Selectivity in Nature
“White” light is
actually a mixture of
all the frequencies of
visible light.
The glass selectively bends the different
frequencies through different angles,
causing the those frequencies or “colors” to
separate from each other.
Selectivity in Nature
Some substances
reflect all the visible
frequencies of light
that fall upon them.
Other substances absorb
all those frequencies. The
absence of reflected light
makes them appear dark.
Selectivity in Nature
Some substances are even more selective.
This surface absorbs
all frequencies except
for red, which it
reflects to our eyes.
This surface looks
blue because blue is
the only frequency
of light it reflects.
Selectivity in Nature
Even “transparent” objects can be more selective.
A blue filter
transmits blue light
only. The other
frequencies are
absorbed.
A less than perfect filter will let small
amounts of the colors it is supposed to
absorb pass on through.
What is “white”?
We know that all the frequencies (colors) of
visible light make “white” when mixed together.
When light falls upon a
rough, textured
surface, it is scattered
in many directions,
mixing the colors well.
This is especially true for grainy crystalline
substances like snow, sugar, and salt.
This is why they look white.
What is “white”?
Actually, you don't need all of the colors to
make white light. Only red, green, and blue
are necessary.
The Primary Colors of Light
That is because the retina of the human eye has
receptors for 3 specific wavelengths (colors) of light.
They are:
red, green,
and blue.
These are called the additive
primary colors.
The Primary Colors of Light
The Science of Color Mixing
Where red and green
spotlights overlap,
the colors combine to
create yellow.
But when red and
green filters overlap,
we get darkness.
Why is this so?
The Science of Color Mixing
No matter whether it's yellow light
or the combination of red and green light,
the same red & green receptors are
stimulated in the retina of the eye.
Either way, it's going to look yellow.
The Science of Color Mixing
The red filter only lets red light through.
The green filter would let green light through
but the red filter already absorbed it.
There is no light that can pass through both
filters to reach the eye.
Subtractive Color Mixing
When you mix paints you think you are
adding colors. What you are really doing is
taking away light.
The pigments in
paints and inks act
like filters that
selectively absorb
certain wavelengths
(colors) of light.
Subtractive Color Mixing
Mix enough paint or stack enough filters and
eventually you will filter out all the light.
The filters shown
here represent the
three primary colors
used in the printing
process: cyan,
magenta, and
yellow.
Primary Colors of Pigments
Notice that the
secondary
colors for
pigments are
identical to the
primary colors
for light.
Rendering Color in Computer Software
The computer sends an RGB signal to the monitor
but must translate it into a CMYK signal for the
printer.
Why Is The Sky Blue?
Molecules in the
atmosphere do a
better job of
scattering blue light
than colors at the
other end of the
spectrum. The light
blue color shows up
well against the
blackness of space.
Thin-film Interference
Another way to filter out colors of light is to
reflect light off from a thin film.
Thin-film Interference
Here, light reflects off from a thin film of oil
on top of water.
Thin-film Interference
Here is the same phenomenon as seen in
soap bubbles.
Different colors
get filtered out
in different
places
according to
how the
thickness of the
soap bubble's
wall will vary.