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Light Fundamentals

Light Fundamentals. By: Rebecca Trout. Facts of Light. Facts of Light. http://4.bp.blogspot.com/_N3bO7M2BWPE/TQ9CMqxwW-I/AAAAAAAAxH0/-aOWEEzjrWw/s1600/spotlight.jpg. Light. Light is the range of frequencies that stimulates the retina of the eye.

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Light Fundamentals

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  1. Light Fundamentals By: Rebecca Trout

  2. Facts of Light Facts of Light http://4.bp.blogspot.com/_N3bO7M2BWPE/TQ9CMqxwW-I/AAAAAAAAxH0/-aOWEEzjrWw/s1600/spotlight.jpg

  3. Light • Light is the range of frequencies that stimulates the retina of the eye. http://farm3.static.flickr.com/2238/2218806734_2c6ba01430.jpg

  4. Light waves • Wavelengths from about 400 nm (4.00 x 10-7 m) to 700 nm (7.00 x 10-7 m) http://www.lightshow.cc/explorer/Images/Lightwaves/light_waves_008.jpg

  5. Colors of light • Shortest wavelengths are seen as violet light. • As wavelengths increase the colors gradually changer to indigo, blue, green, yellow, orange, and red. http://www.windows2universe.org/physical_science/magnetism/images/visible_spectrum_waves_big.jpg

  6. Ray Model The straight-line path of light has led to the ray model. A ray is a straight line that represents the path of a narrow beam of light. The use of ray diagrams is called ray optics or geometric optics

  7. The Speed of Light

  8. Ole Roemer (1644-1710) • First to determine that light does travel with a measurable speed. • Between 1668 and 1674 he made 70 careful measurements of the 42.5- orbital period of Io, one of the moons of Jupiter. http://www.saburchill.com/HOS/astronomy/images/211050002.jpg

  9. Ole Roemer cont. • 1676 – calculated that light took 22 minutes to cross the diameter of Earth’s orbit. • Successfully proved Galileo’s theory that light moved at a finite speed. • Roemer’s value of 22 minutes gives light a speed of abut 220 million meters per second.

  10. Albert A. Michelson (1852-1931) • Between 1880 and the 1920’s: developed Earth based techniques to measure the speed of light. • 1926- time required for light to make a round-trip between 2 California mountains 35 km apart. Best result: 2.997996 +/- 0.00004 x 108 m/s • 1st American to win Science Nobel Prize.

  11. Speed of Light defined • 1960’s development of the laser • New methods of measuring the speed of light. • Speed o a wave is equal to the product of its frequency and wavelength.

  12. Vacuum • Speed of light in a vacuum is such an important and universal value it has its own special symbol, c. • Committee defined the speed of light in a vacuum to be exactly c=299792458 m/s. • Use (3.00 x 108 m/s) for calculations

  13. Sources of Light http://www.siemens.com/press/en/presspicture/?press=/en/presspicture/2008/corporate_communication/media_summit_2008/soaxx200803-04.htm

  14. Difference between a luminous body and an illuminated body. • A luminous body emits light waves. • An illuminated body simply reflects light waves produced by an outside source. http://www.luminous-landscape.com/tutorials/lunar-eclipse.shtml http://urbanext.illinois.edu/kalani/01.cfm

  15. Examples • The sun is luminous. • The moon is illuminated. • A common lamp is luminous because the electrical energy heats a thin tungsten wire in the bulb and causes it to glow. • A bicycle reflector is illuminated because it is designed to reflect automobile headlights.

  16. Luminous flux • The rate at which visible light is emitted from a source is called the luminous flux, P. • The unit of luminous flux is the lumen, lm. • A typical 100-watt incandescent light bulb emits approximately 1750 lm.

  17. Luminous flux cont. • The illumination of a surface is called the illuminance, E, and is the rate at which light falls on a surface. • Illuminance is measured in lumens per square meter, lm/ m2, or lux, lx.

  18. An inverse- square relationship

  19. Luminous intensity • Some light sources are specified in candela, cd, or candle power. • The luminous intensity of a point source is the luminous flux that falls on 1m2 of a sphere 1m in radius. Thus, luminous intensity is luminous flux divided by 4

  20. How to illustrate a surface • Use brighter bulbs, it increases luminous flux. • Move surface closer to bulb, decreasing the distance. • Illuminance: E= P/(4πd²)

  21. Works Cited • Zitzewitz, Paul W. Physics Principles and Problems. 2002 ed. New York: Glencoe, • 2002. Print.

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