Section 18.3 Behavior of Light

Transcription

1 Light and Materials When light hits an object it can be Section 18.3 Behavior of Light Light and Materials Objects can be classified as Transparent Translucent Opaque Transparent, Translucent, Opaque Transparent = Examples: translucent = Examples: Opaque = Examples: Reflection Remember the Law of Reflection Regular reflection = Parallel rays reflect picture Diffuse reflection = Parallel rays picture Refraction Light changes as it enters a new medium If light enters a new medium at an angle, A mirage occurs when light travels through air at Demonstration Describe what happens with the plastic on the window and the slide

2 Polarized Light A polarizing filter will only allow light in Two polarizing filters will block all light Figure 20 page 548 in textbook Polarized Light Polarized glasses are used block Glare is usually Sunglasses are Also used in Why is the sky blue? Small particles in the atmosphere Longer wavelength colors In space, the sun appears Why does the sun look yellow to us? When the blue light is scattered, Why are sunsets and sunrises red/orange? Sunlight travels through Much of the is scattered Longer wavelength Describe the demonstration of the effect of scattering on sunlight

3 Section 18.4 Color What is color? We perceive different of light as different colors The color an object appears depends upon the Colors of and colors of behave differently when mixed We have that detect colors Light Colors White light is made up of White light can be broken up into its colors by The color spectrum can be into white light by a Rainbow can also cause dispersion of light into colors Light Colors You can also change the color of light by A color filter allows some frequencies (colors) of light to but others Demonstration of color filters Diffraction Grating Another way to Different of light diffract at different angles Long waves (red) diffracts at a than short waves (violet) The Color of Objects The color of an object depends on This depends on two things Ex. Figure 24 page 552 in your textbook Mixing Light Colors White light is made up of three primary colors of light are When combined in equal amounts they give Secondary Colors When 2 primary colors are mixed in equal amounts, you get Describe the demonstration of secondary colors of light using filters and overhead

4 Mixing Light Colors Figure 25 page 552 in your textbook Light Colors Now that we know about primary and secondary colors of light, let s revisit the color filters Describe what happens when 2 filters are used together Green + Blue = magenta + red = Red + Green = magenta + green = Blue + Red = magenta + blue = Yellow + Red = cyan + red = Yellow + Green = cyan + green = Yellow + Blue = cyan + blue = Pigments Pigments are materials that are used to Pigments are sometimes called The three primary colors of pigments are Mixing Pigments When all 3 are mixed in equal amounts the result is Mixing Pigments When 2 primary pigments are mixed you get secondary colors of pigments Describe the demonstration of mixing colors of pigments Mixing Pigment Colors Figure 26 page 553 in your textbook Complementary Colors Complementary colors are The pairs of complementary colors are Notice that the pairs are light and pigment. What changes is Complementary Colors What happens when complementary colors are mixed? You will have For light you will get For pigment you will get

5 Section 18.5 Sources of Light How Light Is Produced An object that light is said to be Besides the sun, other sources of light are Incandescent Light Bulbs Most of the light bulbs are probably this type Electric current is The filament Filled with gas to prevent Very actually better at producing than light Fluorescent Light Bulbs Glass tube filled with Glass is coated with located on each end causes mercury to send into phosphor Phosphor absorbs UV and sends out Most of the energy is given off Light produced is Fluorescent Vs. Incandescent Fluorescent bulbs are 18 Watt bulb replaces a Watt is a term not a term Fluorescent bulbs do not as incandescent bulbs Incandescent bulbs produce of visible light and fluorescent bulbs do not Fluorescent bulbs cost than incandescent bulbs Potential problem with fluorescent bulbs and Neon Light Neon lights are actually made Each gas produces is passed through a gas or mixture of gases Gas atoms become excited and Describe demo of Spectrum Tubes

6 Laser Light LASER = Laser light is Coherent light is made up of In coherent light all of the waves Does not from source stays as a Laser Light Vs. Flashlight Laser produces coherent light Flashlight produces incoherent light Sodium Vapor Light Produce light in a way similar to Sodium atoms become excited and Often used in Light produced is in color Demo of sodium chloride in burner flame Sodium Vapor Lamps Figure 29 from textbook page 562 What color does the green truck appear under the orange street light? Tungsten-Halogen Lights Very similar to More Very high More Filled with halogen gas such as Bulb is made with instead of regular glass to withstand higher temps Other Sources of Light vapor lamps lights and lights LED Fireworks Diff. diff colors Demo of different colors chemicals Other Sources of Light Bioluminescence = Chemiluminescence = Demo of light-producing chemical reaction