Week 8: Light and
Color Vision
Facts you may need for the Quiz:
The difference between atomic and thermal
emission.
What a phonton is.
The entropy associated with light.
The spectral response of cones and rods.
How we sense color.
Concept-tests:
8.1 Energy absorbed and emitted by Earth.
8.2 Entropy of energy absorbed and emitted by Earth.
8.3 Additive vs Subtractive color
8.4 The color of shadows
Answers to
Concept Tests
Demos:
NEON LAMP-an example of atomic emission. The lamp emitted red
phontons, which correspond to a specific atomic
transition of electrons in neon atoms. This same
atomic transition is responsible for the red of a
standard helium-neon laser.
INCANDESCENT LIGHT--an example of thermal emission. A current
is sent through a piece of tungsten wire. As the
current is increased the temperature of the wire
increases and the light goes from red to yellow to
white as the temperature increases.
PLASMA BALL AND FLOURESCENT LIGHT--little purple arcs of light
could be seen in the plasma ball, due to thermal
emission. The plasma ball also emitted
electromagnetic waves and excited the atoms in
a flourescent light which I held near the plasma
ball. The gas in the flourescent bulb emits light
due to atomic transitions (most of it is the U.V.),
this light is aborbed by the powder and readmited
in the visible frequencies.
COLOR MIXING PROJECTORS--3 seperate projectors: one producing
red light, one green, and one blue, where shown on a
screen. These are the additive primary colors.
Where all three overlap, we see white (r+g+b=W)--
where red and green over lap we see yellow (r+g=Y), etc.
Colored Filters--These are the primary subtractive colors. The "yellow" filter
absorbs blue. so White-blue = Red + green = yellow.
Links: