Color Color is light's version of pitch i.e. its how the eye perceives the frequency of the electromagnetic radiation between 4.3 x 1014 Hz and 6.7 x 1014 Hz When a stove element is turned on high we notice that it starts to glow "red" hot The radiation from the stove is such that the cells in the retina are stimulated. Objects that glow "white" hot give off radiation over the whole visible spectrum.

If white light is passed through a prism the colors of the visible spectrum are observed. This process is called dispersion.

Chromatic Aberration Since each color has a different wavelength, they are refracted different amounts. The indices of refraction quoted earlier were actually averages for all the colors.

Depends on the combined effect of all its emitted wavelengths. The color of a source of light Depends on the combined effect of all its emitted wavelengths.

Depends on the color of light it reflects. The color of an illuminated object Depends on the color of light it reflects. IT IS IMPORTANT TO NOTE THAT, FOR ANY GIVEN OBJECT, THIS IS NOTALWAYS THE SAME.

Depends on the color of light it transmits The color of a transparent object Depends on the color of light it transmits Filters selectively absorb and transmit different colors.

ROYGBIV Newton formally called the seven colors of the rainbow ELEMENTARY COLORS Newton formally called the seven colors of the rainbow the elementary colors. ROYGBIV

The three elementary colors that produce white light when PRIMARY COLORS The three elementary colors that produce white light when combined are called the primary colors RED, GREEN, and BLUE.

COMPLIMENTARY COLORS Any two colors that combine to produce white are complimentary. YELLOW & BLUE = WHITE CYAN & RED = WHITE MAGENTA & GREEN = WHITE http://www.cbu.edu/~jvarrian/applets/color1/colors_g.htm

PRIMARY PIGMENTS Mixing paints or pigments is a subtractive process opposite to mixing colors. The primary pigments mixed in equal quantities produce black. The primary pigments are YELLOW, CYAN, and MAGENTA.

COLOR VISION The Young- Hemholtz Theory of color vision suggests that the retina has three different types of cone shaped cells on the retina, each sensitive to one of the primary colors. 1821 - 1894 When light enters the eye these cones will be stimulated depending on the color of the light. e.g. a banana would stimulate only the red and green cones.

COLOR BLINDNESS An eye disorder, usually inherited, caused by a disproportionate number of one or more of the color sensitive cone cells. Most common is red-green. e.g. a banana should stimulate the red and green cones equally but a person lacking in green cones would perceive the banana as slightly orange since the brain receives more red stimulus than green.

COLOR TELEVISION Three "electron" guns shoot electrons at a Phosphorescent screen that has hundreds of rows of red, green, and blue filters http://www.colorado.edu/physics/2000/index.pl

http://www.colorado.edu/physics/2000/index.pl

RAINBOWS Rainbows are usually created in the eastern sky after an afternoon thunder shower. White light from the sun enters the raindrops and disperses, partially reflects on the opposite side and is redirected towards the ground where an observer views the rainbow that forms a semi-circle. Because of the path the light takes as it refracts in the raindrop, all observers see the rainbow in a slightly different place in the sky. Sometimes light entering the bottom of the raindrop can reflect internally twice and produce a secondary rainbow that is higher in the sky and much less intense.

http://online. cctt. org/physicslab/content/applets/rainbow/rainbo_z http://online.cctt.org/physicslab/content/applets/rainbow/rainbo_z.htm http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=61

COLOR OF THE SKY AND OTHER RELATED STUFF When the white light from the sun passes through the atmosphere, the colors are scattered (diffracted) by dust, water, etc. The red light, being the longest wavelength, is scattered the least and the blue is scattered the most. The sky takes on a blue color while the sun appears yellow.

At sunset the light has to pass through more atmosphere because of the angle more of the green is scattered and the sun appears orange or reddish orange depending on the humidity, dust, smoke, of the air http://space.about.com/od/astronomynews/a/bluemoon.htm

Clouds scatter most of the light that passes through making them appear white if viewed from above or below if they are very thin grey if they are medium thickness black if they are thunder cloud thick

SPECTROSCOPY The science of studying the spectrum produced by light sources A device for doing this is called a spectroscope. Light is passed through a narrow opening and the light diffracts, each color a different amount due to the different wavelengths

Emission Spectra produced by luminous sources a. continuous spectra produced by incandescent solids, liquids and gases under high pressure b. bright-line spectra produced by gases under low pressure The bright-line spectrum produced by each gas is unique

Absorption Spectra

Note that the absorption spectrum is like a negative of the emission spectrum for each element Emission Spectra Absorption Spectra

Fraunhofer Lines (Solar Spectrum) The chemical composition of the Sun can be determined By analysing the Sun’s Absorption Spectrum. The lines were discovered by Joseph Fraunhofer in 1814

Doppler Effect for Light Since light is a wave like sound, the frequency will shift if the source and observer move relative to each other. If the source is moving away, the light is shifted towards the low frequency end of the spectrum i.e. Red-Shifted If the source is moving towards, the light is shifted towards the high frequency i.e. Blue-Shifted

Big Bang Theory In 1924, Edwin Hubble discovers a galaxy outside Milky Way Also noted that light from distant galaxy was Red-Shifted which means that galaxy is moving away. Further discoveries, showed that more distant galaxies are even more Red-Shifted i.e. they are moving faster. http://video.google.com/videosearch?q=Doppler%20effect&rls=com.microsoft:en-us&oe=UTF-8&startIndex=&startPage=1&um=1&ie=UTF-8&sa=N&hl=en&tab=wv#

The further away the galaxy is the further back in time we are looking The Big Bang is the results of these observations. In 1927 George LeMaitre proposed that the Universe expanded from a single point. Current estimates have the Universe at 13.7 Billion years