Week 6
Explain in the hierarchy of
colors in relation to the energy
of visible light
What is light?
commonly refers to
electromagnetic radiation
that can be detected by the
human eye
How does light travel?
•Light is made up of
bunches of energy called
photons.
•Light travels in waves.
DUAL
PROPERTY OF
LIGHT:
•Light as WAVE
•Light as
PARTICLE
Light as a wave
• A wave has a wavelength, a speed and a
frequency.
• All light travels same speed (in vacuum)
• The energy goes up as frequency goes up
• Color depends on frequency
• Wavelength gets shorter as frequency
goes up
Light as particle
• A photon is like a particle, but it has no
mass
• Think of a photon as a grain of sand.
• We see so many photons at the same time
it’s like seeing all the sand on a beach; we
don’t notice the single grains
• When light hits film in a film camera, it acts
like photons.
Colors of light
• Light is made up of wavelengths of light,
and each wavelength is a particular color.
Different materials
respond differently
when struck by light:
1. Opaque- (Solid)
•Does not let light pass
through.
Materials that light hits can
be:
2. Translucent- (Not
clear)
•Lets some light pass
through.
Materials that light hits can
be:
3. Transparent-
(See-through)
•Lets light pass
through.
Visible Light
RANGE OF WAVELENGHT,
FREQUENCY AND ENERGY OF LIGHT
White Light
•Sunlight is white
light.
•White light = every
color of light
PRISM
•A prism
REFRACTS
white light
into all its
colors!
What
color
light is
refracted
the
most?
Visible Spectrum
•Visible Spectrum = the colors
that you can see.
•All the colors of the rainbow
Visible Spectrum
Red (longest wavelength)
Orange
Yellow
Green
Blue
Indigo
Violet (shortest wavelength)
Addition of Colors
Subtraction of Colors
Wave Properties of Light
Reflection
Refraction
Diffraction
Interference
A. Reflection
Normal
Reflection
incident beam reflected beam
⬥ when a wave
strikes an object
and bounces off
A. Reflection
Law of
Reflection
⬥ the angle of
incidence
equals the
angle of
reflection
B. Refraction
Refraction SLOWER
⬥ bending of waves when
passing from one medium to
another
⬥ caused by a change in speed
FASTER
•slower (more dense) ⇒ light
bends toward the normal
•faster (less dense) ⇒ light
bends away from the normal
B. Refraction
Refraction depends
on…
⬥ speed of light in the
medium
⬥ wavelength of
the light - shorter
wavelengths (blue)
bend more
B. Refraction
Example:
View explanation.
C. Diffraction
Diffraction
⬥ bending of waves
around a barrier
⬥ longer wavelengths
(red) bend more -
opposite of
refraction
D. Interference
Interference
⬥ constructive ⇒ brighter light
⬥ destructive ⇒ dimmer light
Reflection and color
• Why does a green wall look green in
the sunshine?
• A green wall reflects only green light; it
absorbs all the other colors.
• Why does it look different when it’s in
the shade?
• Well, in the dark, it’s black. No light
reflects off it.
Absorption and color
• Why is a black car hotter than a white car in
the summer?
• Remember light is energy. Heat is another
form of energy.
• A white car reflects all wavelengths of light.
• A black car absorbs all wavelengths of light,
absorbing the energy and turning it to heat.
Light transmission
• Transparent materials transmit light, like
windows.
• Remember all light has same speed in vacuum
• Different frequencies have different speeds in
transparent materials – that causes a prism to
separate the colors.
• Colored glass or plastic only transmits the color
that it is; it absorbs or reflects the other colors.
Colorblindness
•Some people have trouble
telling the difference between
colors.
•Their rods and cones do not
detect differences.
The last test is the easiest to
use.
• A person with normal color
vision will see a “5” in the dot
pattern.
• A person with Red/Green color
blindness (the most common)
will see a “2” revealed in the
dots.
Sometimes your eyes get
tired!
•Your rods & cones get used to
what they see and it takes
them some time to go back to
normal.
Which guy is the tallest?
Are these bricks in straight
rows?
Look at the center and move closer
to the screen!
Are the long lines parallel?
Look at the center & move your
head.
Are the purple lines parallel?
Curved or straight?
