Transcript Light
Light 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. Different wavelengths of light have different colors. • Violet light has a wavelength of about 400 nm • Red light has a wavelength of about 700 nm 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) ROYGBIV 1. Red 5. Blue 2. Orange 6. Indigo 3. Yellow 7. Violet 4. Green The speed of light is a set value C = 300,000,000 m/s 8 = 3.00 x 10 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 law • E=P 2 4d • E = illumination • P = luminous flux • d = distance from light source 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... 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 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 • 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. We can only see reflected colors ALL OTHER COLORS ARE ABSORBED SEEING THE LIGHT!! BEHAVIOR OF LIGHT: REFRACTION BEHAVIOR OF LIGHT: REFLECTION LAW OF REFLECTION NORMAL INCIDENT RAY REFLECTED RAY 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 • • • • • Light Amplification by Stimulated Emission of Radiation