Transcript light1
Color and Light Intro question…. How is light different than normal waves?? What is light? Wave or Particle Is light a wave? (ENERGY) Yes Is light a bunch of particles? (Matter) Yes Light is unique, it is what we call an Electromagnetic wave How is light like a particle (matter)? Does not need a medium to travel through Can travel through a vacuum high energy (intensity of light) does not effect light the same way as normal waves Energy associated w/ frequency rather than amplitude Light consists of Photons- massless bundles of concentrated electromagnetic energy Photoelectric effect Ejection of electrons from certain metals when exposed to certain frequencies of light How is light like a wave? Light can diffract (bend around stuff) Cannot travel through polar filters Can exhibit Doppler Effect (change freq. Depending on motion of source) Can interfere (constructive or destructive) (bend when travelling between diff. Media) and refract Has no mass We refer to all of this as the dual nature of light This means………. Light is special Electromagnetic Waves Light is the oscillation of electric and magnetic fields Shake an elctircally charged rod then you will create an EM wave Must always have same speed… otherwise Electric Field and Mag. Field would reinformce each other to infinity or destroy each other Many diff. Kinds of “light” A wide spectrum of types of light that we call Electromagnetic Radiation These include…… infrared, radio, ultraviolet, gamma rays, microwaves, x-rays, & visible light All exhibit same exact characteristics but vary b/c of wavelength & frequency All types travel at the same speed at The speed of light….300,000,000 m/s We can only ‘see’ the small portion that is ‘visible light’ The rest is invisible to the human eye Electromagnetic Spectrum http://www.youtube.com/watch?v=i8ca Gm9Fmh0&list=PL09E558656CA5DF76 &safe=active Visible Light Wavelength range From about 700 nm to 400 nm 1 nm= 1 x 10^-9 m Different colors have different wavelengths & frequencies Infinite amount of different colors ROYGBIV Absence of Light?? Black or White?? White is combination of all colors of light Black is complete lack of light, all colors have been taken away Black would be the absence of Light!! Transparent Materials Glass- natural vibration frequency in the U-V range Produces large amplitudes and energy is lost as heat UV light cannot travel through glass Visible light vibrates electrons w/ smaller amplitude so less collisions and less transfer as heat. So light will be reemitted as light Time delay between absorbtions and reemissions causes light to move more slowly through glass than through a vacuum Opaque Materials Most materials there is no reemission, and light Energy is converted to Heat Vibrations of the electrons are not passed from atom to atom through the bulk of the material; rather the electrons vibrate for short periods of time and then reemit the energy as a reflected light wave Metals are opaque- free electrons will vibrate easily and reflects light…. This is why metals are shiny Shadows Shadows formed where light cannot reach Sharp shadows- close light source Blurry shadows- fuzzy on the outside, more dark on the inside Umbra- total Shadow Penumbra- partial shadow… some light blocked but other light fills in Shadows Polarization of Light Light waves are transverse Electrons vibrate and create a wave in the direction of the vibration polarized Since the electrons vibrate in random directions normal light is not polarized If light shines on a polarizing filter, only the light waves in the direction of the polarization axis can get through If two filters overlap at right angles, no light can get through Dispersion Dispersion--the breaking up of light into its component colors when travelling through a prism Why does it happen different wavelengths (colors) of light travel through a medium at different speeds, the amount of bending is different for different wavelengths. Violet (short ) is bent the most and red(long ) the least short wavelengths travel more slowly (lower frequency) through a medium than longer ones do its colors can be separated (dispersed) by this difference in behavior. Prisms Any transparent substance that can separate colors Red bent least, violet most Recomposition Opposite of dispersion Combining of colors of light using a lens or mirrors to form white light Newton’s Disk exhibits recomposition Series of mirrors Newtons Disk When spun fast enough all the colors will turn white Utililizes the principle of persistence of vision Human eye retains an image for 1/30th of a second Connection… wheels on tv Fiber optic blinker How we see things….Subtractive Theory of Light Keep taking away colors until you wind up w/ one Objects absorb every color other than the color it appears However, most colors we see are various combinations of colors Ex. A blue shirt may reflect mostly blue, some purple, maybe some green, depending on the shade it appers What happens when light goes through filters Objects we see act like light filters Colors combine the same way that pigments/paints do Subtractive Theory of Light Filters & Pigments Why are objects different colors? Is a certain object always going to be a certain color no matter what?? Depends on what kind of light is hitting it Additive theory of light Add colors of light to each other until one is made Simple adding of different colors of light, no filters involved • Ex. TVs, • projectors Why does white light look white? Additive v. Subtractive Color Mixing Subtractive Primary Colors • Cyan- reflects green & blue • Yellow - reflects red & green • Magenta – reflects red & blue – So if you overlap a red filter w/ a blue filter you will wind up with Magenta Additive color mixing with red, blue, and green additive primary colors. When different colored spotlights overlap in a dark room, additive mixing occurs. If the commonly used additive primary colors red, green, and blue all overlap in effectively equal mixture, white light is produced at the center. Additive color mixing is conceptually simpler than the subtractive color mixing you get with paints and pigments since you are just adding light energy in different ranges of the visible spectrum. Additive and Subtractive Color Mixing Animations http://www.physics-chemistry-interactive-flashanimation.com/optics_interactive/additive_color_model_mixing_synthesis.htm http://www.physics-chemistry-interactive-flashanimation.com/optics_interactive/subtractive_color_model_mixing_synthesis.htm • Art class color wheel?? Colors of Objects http://www.physics-chemistry-interactive-flashanimation.com/optics_interactive/colours_of_objects.htm Complementary Colors • Two colors that will combine to make white light • Negative images – Will show the original colors complement – Red & cyan, blue & yellow, green & magenta