LightLightLightLight Chapter 28

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.

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.

Electromagnetic Spectrum 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

Color Spectrum (from longest to shortest wavelengths) Color Spectrum (from longest to shortest wavelengths) ROYGBIV 1. Red 1. Red 2. Orange 2. Orange 3. Yellow 3. Yellow 4. Green 4. Green 5. Blue 5. Blue 6. Indigo 6. Indigo 7. Violet 7. Violet

The speed of light is a set value C = 300,000,000 m/s = 3.00 x 10 8 m/s = 300,000 km/s = 186,000 mi./s

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.

Olaf Roemer was the second to try Used time it took Jupiter’s moon Io to eclipse Jupiter. Recorded the time it took Io to emerge from behind Jupiter. As the Earth moved further and further away from Jupiter, the longer it took.

First American Nobel prize winner: Albert Michelson For his measurement of the speed of light Results were within.001 % of currently accepted speed of light

Michelson’s Technique Technique was to use two mountain peaks in California 35 km apart, then time how long it took light to bounce back. Used an interferometer for timing device

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 intensity of light Determined by the inverse square lawDetermined by the inverse square law E = P  4  d 2 E = illuminationE = illumination P = luminous fluxP = luminous flux d = distance from light sourced = distance from light source

Transparent Objects Allow light to pass through them undisturbed.Allow light to pass through them undisturbed. No trouble identifying objects behind transparent objects.No trouble identifying objects behind transparent objects. Examples: glass, transparencies, clear liquidsExamples: glass, transparencies, clear liquids

Translucent Objects Light can pass through, but not clearly.Light can pass through, but not clearly. Reflect some light, but also allow some light to pass through (transmit)Reflect some light, but also allow some light to pass through (transmit) Examples: tissue paper, lampshades, frosted light bulbs...Examples: tissue paper, lampshades, frosted light bulbs...

Opaque Objects Materials which do not allow light to pass through.Materials which do not allow light to pass through. Only reflect light.Only reflect light. Examples: bricks, doors, people...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...

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

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

Primary Pigments These are opaque and luminous magentacyan YellowCompose 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.

We can only see reflected colors

ALL OTHER COLORS ARE ABSORBED

SEEING THE LIGHT!!

BEHAVIOR OF LIGHT: REFRACTION

BEHAVIOR OF LIGHT: REFLECTION

INCIDENT RAY REFLECTED RAY NORMAL LAW OF REFLECTION

DIFFRACTION: Bending of light through a narrow slit

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.

Optical Systems Use: –Lenses –Mirrors –Prisms –Monochromatic substances –Lasers

LASER L ight A mplification by S timulated E mission of R adiation