Chapter 16 – Light What type of wave is light? (last chapter)

ELECTROMAGNETIC SPECTRUM Contains only transverse waves All forms of light are included EM spectrum usually shown from low frequency to high frequency –this also means that the wavelength goes from long to short on the same scale No medium is required for these waves to travel

Radio wave Micro wave Infrared (IR) Visible ROYGBIV Ultraviolet (UV) X-waveGamma wave Commun ication (radio, cell phone, satellite) Commun ication Heat food Remote control Thermal imaging What we see “black light” Sun X-rayLarge stars Nuclear reaction EM Spectrum

“KINDA NEW” EQUATION c =  c : speed of light (3x10 8 m/s) : wavelength (m) : frequency (Hz)

Types of Materials Opaque: –material absorbs/reflects all of the light –no light gets through (ex. Brick) Translucent: –material absorbs/reflects some of the light –most light gets through (ex.lamp shade) Transparent: –material absorbs/reflects none of the light –all light passes through (ex. glass)

Confusing Vocabulary Luminous: an object that emits light Illuminated: an object that reflects light Luminous flux [  ]: the rate at which light is emitted Lumens (lm): the unit for luminous flux Illuminance [E]: the amount of light incident on a surface Lux (lx): the unit for illuminance

Illuminance Equation  E = 4  r 2 where: E is illuminance (lux)  is luminous flux (lumens) r is the distance from the source (meters)

Producing Light Incandescent –A piece of metal in a closed space is heated by electricity –Filament (glowing metal) made of tungsten Fluorescent –An electric current is sent through a gas (mercury and argon) in a closed space –Similar to lightning All artificial producers of light follow one of these two methods. The only exception is a laser.

COLORS & PIGMENTS OF LIGHT Additive color process – all three colors of light have the correct intensities, they appear white. Primary colors:. –red –green –blue Primary Pigments – absorbs only one primary color and reflects two from white light. –yellow (absorbs blue, reflects red and green) Secondary pigments – absorbs two primary colors and reflects one (red, green., and blue)

Polarization Light is a transverse wave that oscillates in more than one direction Polarization is when light is forced to choose one particular direction of oscillation (light coming off of a road is reflected and becomes polarized). Ex. – polarized sunglasses – keeps the glare off Types: –Vertical and horizontal (most common) –Clockwise and counterclockwise

Ch 16 Homework lux x10 8 m Watts lm ,000 km x10 -7 m 62. Vertically m m 68. light takes 5  s, while sound takes 4.7 s