1 / 10

Light and Color

Light and Color. light has both wave and particle characteristics l = wavelength; n = frequency c = speed of light = ln = 3.00 x 10 8 m/s visible: l ~400 nm (violet) - ~750 nm (red) energy in light comes in “packets” (particles?) called “photons”

dgirard
Télécharger la présentation

Light and Color

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Light and Color • light has both wave and particle characteristics • l = wavelength; n = frequency • c = speed of light = ln = 3.00 x 108 m/s • visible: l ~400 nm (violet) - ~750 nm (red) • energy in light comes in “packets” (particles?) called “photons” • Ephoton = hn = hc/l (h = Planck’s Constant) • different color = different l = different E per photon Light & Color

  2. Light & Color https://en.wikipedia.org/wiki/Visible_spectrum

  3. Light and Color (cont.) • white light = mixture of all different visible l’s of light (the whole rainbow) • all different kinds of photons, in roughly the same numbers, reach our eyes • monochromatic light = light of one wavelength (color) • atomic emission line, laser pointer light • most colored light is polychromatic: a mixture of different colors (l), but not ALL l’s in equal numbers. We see the “blended” (or sometimes just the most dominant) color Light & Color

  4. Photons can be absorbed or emitted • Emission of a photon: if energy is released by an atom AS a photon • PE of atom goes down; energy “turned into” a photon (creates one) • Absorption of a photon: an atom or molecule absorbs the energy of a photon and the photon “disappears” • PE goes up (at least initially) • “endothermic” Light & Color

  5. Recall: H atom emission (1st semester) Ephoton Light & Color

  6. Selective Absorption “Causes” Things to Appear Colored • If white light shines on (or through) a substance (or solution), and only certain kinds of photons (i.e., colors of light) are absorbed, the light that makes it to our eyes will be perceived as having a “color”! Light & Color

  7. Trichromatic Color Theory https://en.wikipedia.org/wiki/Cone_cell • (see sheet) • All colors can be thought of as different mixtures of three primary colors: R, G, B • our eyes have receptor molecules that are sensitive to the absorption of these three colors, basically • In equal amounts: • R + B = M (magenta) • B + G = C (cyan) • R + G = Y (yellow) (Seems odd!) • In different amounts, all different colors • Colors on Computer! Projection TV’s Light & Color

  8. Absorption Spectrum • Plot of Absorbance (Abs) vs. Wavelength • The larger the “absorbance”, the greater the relative number of photons (of that wavelength) being absorbed by the sample. • If primarily R is being absorbed, G and B are transmitted (or reflected), and we see B + G = C • If primarily G is being absorbed, R and B are transmitted and we see R + B = M • If primarily B is being absorbed, R and G are transmitted, and we see R + G = ____ • See handout with spectra Light & Color

  9. Light & Color

  10. Absorption at the Molecular Level • Absorption of one photon of visible light corresponds to the excitation of one electron from a lower energy orbital to a higher energy one • The bigger the DE (energy difference or gap) between the orbitals, the greater the Ephoton absorbed • Different gaps yield different colors absorbed, and thus different colors perceived • Changing the DE in a metal complex (or other “dye” molecule) will change the color of the complex (or dye) Light & Color

More Related