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Light & Color

Light is an electromagnetic wave

• Electric field waves perpendicular to Magnetic field waves.

• Both are perpendicular to direction wave is traveling.

• This makes it a transverse wave.

Electromagnetic Spectrum (longest wavelength to shortest wavelength)

1. Radio and TV 2. Microwaves 3. Infrared 4. Visible

5. Ultraviolet 6. X-rays 7. Gamma Rays

• Violet light has a wavelength of about 400 nm• Red light has a wavelength of about 700 nm

Different wavelengths of light have different colors.

Color Spectrum (from longest to shortest wavelengths)

ROYGBIV 1. Red

2. Orange

3. Yellow

4. Green

5. Blue

6. Indigo (Now

a Goner!)

7. Violet

Galileo was first to try to measure speed of light.

• Before Galileo, everyone thought light had no speed

• Galileo first to hypothesize light had a finite speed

• Used lanterns with shutters as first experiment.

• Decided light was too fast to measure.

Speed of light, wavelength of light, frequency of light relationship

c = f• c = speed of light (m/s)• = wavelength of light (m)• f = frequency of light (Hz)

The speed of light is a set value

C = 300,000,000 m/s = 3.00 x 108 m/s = 300,000 km/s = 186,000 mi./s

Transparent Objects• Allow light to pass through them

undisturbed.• No trouble identifying objects

behind transparent objects.• Examples: glass, transparencies,

clear liquids

Translucent Objects• Light can pass through, but not

clearly.• Reflect some light, but also allow

some light to pass through (transmit)

• Examples: tissue paper, lampshades, frosted light bulbs...

Opaque Objects

• Materials which do not allow light to pass through.

• Only reflect light.• Examples: bricks, doors,

people...

Luminous

• Objects which create light are said to be Luminous

• Examples: Sun, stars, light bulbs

ILLUMINATED

• Objects which reflect light• These objects do not create their own light• examples: Moon, planets, desk, whiteboard,

people...

Color of Light

Making Colors by Addition of Light

Primary Light Colors

• Three colors:• Red, blue, green• Combinations of any of these two produce

secondary colors, all three colors added together make white light

• These are illumines and create their own light

Light Color addition

Red + Blue = Magenta

Blue + Green = Cyan

Green + Red = Yellow

Venn Diagram of Color

Light color addition (cont.)

• Color monitors and TV screens use this principle

• By varying the intensity of the three colors, any pixel can have any color possible.

Making Colors by Subtraction

Pigments

Primary Pigments

• These are opaque and luminous• Compose of magenta, cyan, and

Yellow• Absorb and reflect light rather

then illuminate it.• Mixtures of paints from these

primary color pigments can produce any color imaginable.

Venn Diagram of Pigment

WHAT WE SEE?Reflected v. Absorbed

We can only see reflected colors

ALL OTHER COLORS ARE ABSORBED

BEHAVIOR OF LIGHT:

REFRACTION

BEHAVIOR OF LIGHT:

REFLECTION

GIVING LIGHT DIRECTION:

POLARIZATION

Polarization of Light• Unpolarized light vibrates in all directions

in the xyz plane.• In this illustration the electric field (E) is

vibrating on the y-axis, and the Magnetic field (B) is vibrating on the z-axis. The wave is traveling along the x-axis.

Polarization (cont.)

• Polarizers are made of long strands of molecules that are all aligned parallel to each other.

• Look at blue in the illustration.

Polarizers will only allow light that is vibrating parallel to the direction the

polarizer is ligned up. Polarizers will not allow light to pass through if it is vibrating

perpendicular to it.