Light FundamentalsLight Fundamentals

By: Rebecca TroutBy: Rebecca Trout

Facts of Light

Facts of Light

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LightLight

Light is the range of frequencies Light is the range of frequencies that stimulates the retina of the that stimulates the retina of the eye.eye.

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Light wavesLight waves Wavelengths from about 400 nm Wavelengths from about 400 nm

(4.00 x 10(4.00 x 10-7-7 m) to 700 nm (7.00 x m) to 700 nm (7.00 x 1010-7-7 m) m)

http://www.lightshow.cc/explorer/Images/Lightwaves/light_waves_008.jpg

Colors of lightColors of light

Shortest wavelengths are seen Shortest wavelengths are seen as violet light.as violet light.

As wavelengths increase the As wavelengths increase the colors gradually changer to colors gradually changer to indigo, blue, green, yellow, indigo, blue, green, yellow, orange, and red.orange, and red.

http://www.windows2universe.org/physical_science/magnetism/images/visible_spectrum_waves_big.jpg

Ray ModelRay Model

The straight-line path of light has The straight-line path of light has led to the ray model.led to the ray model.

A ray is a straight line that A ray is a straight line that represents the path of a narrow represents the path of a narrow beam of light.beam of light.

The use of ray diagrams is called The use of ray diagrams is called ray optics or geometric opticsray optics or geometric optics

The Speed of Light

Ole Roemer (1644-1710)Ole Roemer (1644-1710)

First to determine that light does First to determine that light does travel with a measurable speed.travel with a measurable speed.

Between 1668 and 1674 he Between 1668 and 1674 he made 70 careful measurements made 70 careful measurements of the 42.5- orbital period of Io, of the 42.5- orbital period of Io, one of the moons of Jupiter.one of the moons of Jupiter.

http://www.saburchill.com/HOS/astronomy/images/211050002.jpg

Ole Roemer cont.Ole Roemer cont.

1676 – calculated that light took 1676 – calculated that light took 22 minutes to cross the 22 minutes to cross the diameter of Earth’s orbit.diameter of Earth’s orbit.

Successfully proved Galileo’s Successfully proved Galileo’s theory that light moved at a finite theory that light moved at a finite speed.speed.

Roemer’s value of 22 minutes Roemer’s value of 22 minutes gives light a speed of abut 220 gives light a speed of abut 220 million meters per second.million meters per second.

Albert A. Michelson (1852-Albert A. Michelson (1852-1931)1931) Between 1880 and the 1920’s: Between 1880 and the 1920’s:

developed Earth based techniques developed Earth based techniques to measure the speed of light.to measure the speed of light.

1926- time required for light to make 1926- time required for light to make a round-trip between 2 California a round-trip between 2 California mountains 35 km apart. Best result: mountains 35 km apart. Best result: 2.997996 +/- 0.00004 x 102.997996 +/- 0.00004 x 1088 m/s m/s

1st American to win Science Nobel 1st American to win Science Nobel Prize.Prize.

Speed of Light definedSpeed of Light defined

1960’s development of the laser1960’s development of the laser New methods of measuring the New methods of measuring the

speed of light.speed of light. Speed o a wave is equal to the Speed o a wave is equal to the

product of its frequency and product of its frequency and wavelength.wavelength.

VacuumVacuum

Speed of light in a vacuum is Speed of light in a vacuum is such an important and universal such an important and universal value it has its own special value it has its own special symbol, symbol, c.c.

Committee defined the speed of Committee defined the speed of light in a vacuum to be exactly light in a vacuum to be exactly cc=299792458 m/s. =299792458 m/s.

Use (3.00 x 10Use (3.00 x 108 8 m/s) for m/s) for calculations calculations

Sources of Light

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

Difference between a luminous Difference between a luminous body and an illuminated body.body and an illuminated body.

A A luminousluminous body emits light body emits light waves.waves.

http://www.luminous-landscape.com/tutorials/lunar-eclipse.shtml

http://urbanext.illinois.edu/kalani/01.cfm

AnAn illuminated illuminated body simply reflects body simply reflects light waves produced by an outside light waves produced by an outside source.source.

ExamplesExamples

The sun isThe sun is luminous luminous.. The moon isThe moon is illuminated illuminated.. A common lamp is A common lamp is luminousluminous

because the electrical energy because the electrical energy heats a thin tungsten wire in the heats a thin tungsten wire in the bulb and causes it to glow.bulb and causes it to glow.

A bicycle reflector is A bicycle reflector is illuminatedilluminated because it is designed to reflect because it is designed to reflect automobile headlights. automobile headlights.

Luminous fluxLuminous flux

The rate at which visible light is The rate at which visible light is emitted from a source is called emitted from a source is called the the luminous fluxluminous flux, , P.P.

The unit of luminous flux is the The unit of luminous flux is the lumen, lumen, lm.lm.

A typical 100-watt incandescent A typical 100-watt incandescent light bulb emits approximately light bulb emits approximately 1750 lm. 1750 lm.

Luminous flux cont.Luminous flux cont.

The illumination of a surface is The illumination of a surface is called the called the illuminanceilluminance, , E, E, and and is the rate at which light falls on is the rate at which light falls on a surface.a surface.

Illuminance is measured in Illuminance is measured in lumens per square meter, lm/ lumens per square meter, lm/ mm22, or , or luxlux, lx., lx.

An inverse- square An inverse- square relationshiprelationship

Luminous intensityLuminous intensity

Some light sources are specified Some light sources are specified in in candelacandela, cd, or candle power., cd, or candle power.

The luminous intensity of a point The luminous intensity of a point source is the luminous flux that source is the luminous flux that falls on 1mfalls on 1m22 of a sphere 1m in of a sphere 1m in radius. Thus, luminous intensity radius. Thus, luminous intensity is luminous flux divided by 4is luminous flux divided by 4

How to illustrate a surfaceHow to illustrate a surface

Use brighter bulbs, it increases Use brighter bulbs, it increases luminous flux.luminous flux.

Move surface closer to bulb, Move surface closer to bulb, decreasing the distance.decreasing the distance.

Illuminance: E= P/(4πd²) Illuminance: E= P/(4πd²)

Works Cited

Zitzewitz, Paul W. Physics Zitzewitz, Paul W. Physics Principles and Problems. 2002 Principles and Problems. 2002 ed. New York: Glencoe, ed. New York: Glencoe,

2002. Print.2002. Print.