Electromagnetic Waves and Color

PhysicsMs. Shaver

Color

•Color is the perceptual quality of light.

• The human eye

can distinguish almost ten million colors.

Types of Materials

Transparent light passes thru without scattering TranslucentLight passes thru diffusely (scatters in all directions)

Color comes to our eyes from objects due to:

• Emission• Reflection• Transmission• Interference• Dispersion• Scattering

Emission: the object itself is a source of light.

Reflection: certain

frequencies are

reflected from the object,

others are absorbed.

A particular material absorbs the light frequency that matches the frequency at which electrons in the atoms of that material vibrate.

• The energy of the frequency absorbed turns to heat.

Transmission: certain frequencies are transmitted through the object, others

are absorbed.

Scattering: the

reradiation of certain

frequencies of light, striking

small, suspended particles.

Interference: constructive and destructive interference.

Dispersion: the angular

separation of a light wave

during refraction.

Why do we see the colors of the rainbow?

Light and water paint the Rainbow in the sky

When raindrop A disperses light, only the red light exits at the correct angle to travel to the observer's eyes. The other colored beams exit at a lower angle, so the observer doesn't see them. The sunlight will hit all the surrounding raindrops in the same way, so they will all bounce red light onto the observer.

Raindrop B is much lower in the sky, so it doesn't bounce red light to the observer. At its height, the violet light exits at the correct angle to travel to the observer's eye. All the drops surrounding raindrop B bounce light in the same way. The raindrops in between A and B all bounce different colors of light to the observer, so the observer sees the full color spectrum.

Why is the sky blue?

Why the sky is blue

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.  When we look towards the sun at sunset, we see red and orange colors because the blue light has been scattered out and away from the line of sight.

Why is the ocean sometimes blue, gray or

green?

Ocean ColorThe red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light we see is composed of the shorter wavelength blues and violets.

microscopic marine algae, called phytoplankton, have the capacity to absorb light in the blue and red region of the spectrum owing to specific pigments like chlorophyll. Accordingly, as the concentration of phytoplankton increases in the water, the color of the water shifts toward the green part of the spectrum.

Fine mineral particles like sediment absorb light in the blue part of the spectrum, causing the water to turn brownish in case of massive sediment load.

Primary Colors of Light

http://photographycourse.net/wp-content/uploads/2008/03/rgb_illumination-300x225.jpg

Primary Colors of Light: Red, Green, Blue-combine to white

Secondary colors of Light:cyan, magenta, and yellow-

also combine to white.

• A complementary color is formed by subtracting a primary color from white light.

• Every secondary color is the complement of a primary color.

If a blue and yellow flashlight strike a white object at the same time, what color will the object

appear?

Blue + yellow = white since yellow light contains green and red.

If red is subtracted from white, what color remains?

Cyan

What color will a blue ball appear if a red light only

strikes it and why?

=>

Color of light is an additive process with respect to

frequency. Why?

• The primary colors when added together give white light.

Additive Color of Light Mixing Applications

• Movie film • Slide projector • Television and computer displays

Primary Colors of Pigment(Cyan, Yellow, Magenta combine

to give Black color pigment)

Notes

• The primary colors of pigment are the secondary colors of light and vice versa.

When magenta and cyan pigments are mixed what

color results?

Pigment is a subtractive color process. Why?

• Colors are formed by absorbing (taking away) certain frequencies from white light.

• The absence of a reflected light wave appears as black color.

Applications: painting, printing, etc.

Example: What makes a leaf green

• A green leaf reflects green light• A green leaf has chlorophyll that

absorbs red and blue light