Light from the Sun
Physics 10
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Additive Primary Colors
⇒ The sun emits light of all frequencies.
⇒ However, the sun is brightest in the yellow-green
part of the spectrum.
⇒ Our eyes have evolved to be most sensitive in
this range of frequencies.
Additive Primary Colors
⇒ Red, green, and blue are called the additive
primary colors.
red + blue = magenta
red + green = yellow
⇒ Our eyes have three types of cones that detect
light of low (red), medium (green), and high (blue)
⇒ If all three types of cones are stimulated equally,
we perceive white light.
blue + green = cyan
⇒ Varying amounts of each can be added together
to form any other color.
Exercise 20
Exercise 20
Complete the following equations:
Using the figure to
the left, complete
the following
Yellow light + blue light = _______ light.
Green light + _______ light = white light.
Magenta + yellow + cyan = ________ light.
Exercise 13
Supposed two flashlight beams are shown on a white
screen, one beam through a pane of blue glass and
the other through a pane of yellow glass. What
color appears on the screen where the two beams
overlap? Suppose, instead, that the two panes of
glass are placed in the beam of the single flashlight.
What then?
⇒ The overlapping blue and yellow beams will
produce white light. When the two panes of
glass are overlapped and placed in front of a
single flashlight, however, little or no light will
be transmitted.
Yellow light + blue light = _______ light.
Green light + _______ light = white light.
Magenta + yellow + cyan = ________ light.
⇒ Yellow light + blue light = white light.
Green light + magenta light = white light.
Magenta + yellow + cyan = white light.
Subtractive Primary Colors
⇒ Mixing colored pigments in paints and dyes is entirely
different than mixing colors.
⇒ The colors, magenta,
cyan, and yellow are called
the subtractive primary
⇒ All color photographs in
books are the result of
magenta, cyan, and yellow
⇒ The rules of color subtraction are different from the rules
of light addition.
Exercise 40
You're explaining to a youngster at the seashore
why the water is cyan colored. The youngster
points to the whitecaps of overturning waves and
asked why they are white. What is your answer?
⇒ The water is broken up into a multitude
of different size droplets when the wave
breaks, and like the droplets in clouds
overhead, light of many visible frequencies
is scattered to produce the white color.