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Color and Light
Intro question…. How is light different than normal
waves??
What is light? Wave or Particle
Is light a wave? (ENERGY)
Yes
Is light a bunch of particles? (Matter)
Yes
Light is unique, it is what we call an
Electromagnetic wave
How is light like a particle (matter)?
Does not need a medium to travel through
Can travel through a vacuum
 high energy (intensity of light) does not
effect light the same way as normal waves
Energy associated w/ frequency rather than
amplitude
Light consists of Photons- massless bundles
of concentrated electromagnetic energy
Photoelectric effect
Ejection of electrons from certain metals when
exposed to certain frequencies of light
How is light like a wave?
Light can diffract (bend around stuff)
Cannot travel through polar filters
Can exhibit Doppler Effect (change freq. Depending
on motion of source)
Can interfere
(constructive or destructive)
(bend when travelling between diff. Media)
and refract
Has no mass
We refer to all of this as the dual nature of light
This means………. Light is special
Electromagnetic Waves
Light is the oscillation of electric and
magnetic fields
Shake an elctircally charged rod then you
will create an EM wave
Must always have same speed… otherwise
Electric Field and Mag. Field would
reinformce each other to infinity or destroy
each other
Many diff. Kinds of “light”
 A wide spectrum of types of light that we call
Electromagnetic Radiation
 These include…… infrared, radio, ultraviolet, gamma
rays, microwaves, x-rays, & visible light
 All exhibit same exact characteristics but vary b/c of
wavelength & frequency
 All types travel at the same speed
at The speed of light….300,000,000 m/s
 We can only ‘see’ the small portion that is
‘visible light’
 The rest is invisible to the human eye
Electromagnetic Spectrum
http://www.youtube.com/watch?v=i8ca
Gm9Fmh0&list=PL09E558656CA5DF76
&safe=active
Visible Light
 Wavelength range From about 700 nm to 400 nm
 1 nm= 1 x 10^-9 m
 Different colors have different wavelengths & frequencies
 Infinite amount of different colors
 ROYGBIV
Absence of Light??
Black or White??
White is combination of all colors of
light
Black is complete lack of light, all colors
have been taken away
Black would be the absence of Light!!
Transparent Materials
Glass- natural vibration frequency in the U-V range
Produces large amplitudes and energy is lost as heat
UV light cannot travel through glass
Visible light vibrates electrons w/ smaller amplitude
so less collisions and less transfer as heat. So light
will be reemitted as light
Time delay between absorbtions and reemissions causes
light to move more slowly through glass than through a
vacuum
Opaque Materials
 Most materials there is no reemission, and light Energy is
converted to Heat
 Vibrations of the electrons are not passed from atom to
atom through the bulk of the material; rather the electrons
vibrate for short periods of time and then reemit the energy
as a reflected light wave
 Metals are opaque- free electrons will vibrate easily and
reflects light…. This is why metals are shiny
Shadows
Shadows formed where light cannot reach
Sharp shadows- close light source
Blurry shadows- fuzzy on the outside, more dark
on the inside
Umbra- total Shadow
Penumbra- partial shadow… some light blocked
but other light fills in
Shadows
Polarization of Light
 Light waves are transverse
 Electrons vibrate and create a wave in the direction of
the vibration
 polarized
 Since the electrons vibrate in random directions normal
light is not polarized
 If light shines on a polarizing filter, only the light waves
in the direction of the polarization axis can get through
 If two filters overlap at right angles, no light can get
through
Dispersion
Dispersion--the breaking up of light into its
component colors when travelling through a prism
Why does it happen
different wavelengths (colors) of light travel through a
medium at different speeds, the amount of bending is
different for different wavelengths.
Violet (short ) is bent the most and red(long ) the least
short wavelengths travel more slowly (lower frequency)
through a medium than longer ones do
its colors can be separated (dispersed)
by this difference in behavior.
Prisms
Any transparent substance that can
separate colors
Red bent least, violet most
Recomposition
Opposite of dispersion
Combining of colors of light using a lens or
mirrors to form white light
Newton’s Disk exhibits recomposition
Series of mirrors
Newtons Disk
When spun fast enough all
the colors will turn white
Utililizes the principle of
persistence of vision
Human eye retains an image
for 1/30th of a second
Connection… wheels on tv
Fiber optic blinker
How we see things….Subtractive
Theory of Light
Keep taking away colors until you wind up w/ one
Objects absorb every color other than the color it
appears
However, most colors we see are various combinations of
colors
Ex. A blue shirt may reflect mostly blue, some purple,
maybe some green, depending on the shade it appers
What happens when light goes through filters
Objects we see act like light filters
Colors combine the same way that
pigments/paints do
Subtractive Theory of Light
Filters & Pigments
Why are objects different colors?
Is a certain object always going to be a certain
color no matter what??
Depends on what kind of light is hitting it
Additive theory of light
Add colors of light to each other until one
is made
Simple adding of different colors of light,
no filters involved
• Ex. TVs,
• projectors
Why does white light look white?
Additive v. Subtractive Color Mixing
Subtractive Primary Colors
• Cyan- reflects green & blue
• Yellow - reflects red & green
• Magenta – reflects red & blue
– So if you overlap a red filter w/ a blue filter you
will wind up with Magenta
Additive color mixing with
red, blue, and green
additive primary colors.
When different colored
spotlights overlap in a dark
room, additive mixing occurs. If
the commonly used additive
primary colors red, green, and
blue all overlap in effectively
equal mixture, white light is
produced at the center.
Additive color mixing is
conceptually simpler than the
subtractive color mixing you
get with paints and pigments
since you are just adding light
energy in different ranges of
the visible spectrum.
Additive and Subtractive Color Mixing Animations
http://www.physics-chemistry-interactive-flashanimation.com/optics_interactive/additive_color_model_mixing_synthesis.htm
http://www.physics-chemistry-interactive-flashanimation.com/optics_interactive/subtractive_color_model_mixing_synthesis.htm
• Art class color wheel??
Colors of Objects
http://www.physics-chemistry-interactive-flashanimation.com/optics_interactive/colours_of_objects.htm
Complementary Colors
• Two colors that will combine to make white
light
• Negative images
– Will show the original colors complement
– Red & cyan, blue & yellow, green & magenta