The nature of light
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Transcript of The nature of light
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LightThe Nature and Colors of Light
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The Electromagnetic Spectrum
Light waves are electromagnetic wavesLight waves consist of periodically changing electric
and magnetic fieldsProduced by accelerating charged particles
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The Electromagnetic Spectrum
The complete range of frequencies and wavelengths of EM waves
Visible light is only a small portion of the spectrumVarious kinds are classified according to the
methods by which they are generated or received
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https://classconnection.s3.amazonaws.com/255/flashcards/4013255/jpg/electromagneticspectrum-141B490BAC872789434.jpg
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Speed of Light
c represents the speed of light
c = 3.00x108 m/s
The speed of light in a material is always less than c
v=fλ applies to light waves
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Reflection
Wave changes direction upon hitting a
reflecting surface
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0ri
R
N
I
R= reflecting rayr= angle of reflectionI= incident rayi= angle of incidenceN= normal
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Law of Reflection
θi= θr
States that waves are reflected from the boundary of the medium at the same angle at
which they strike it
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Refraction
Wave changes direction upon
entering a medium of different density
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Absolute index of Refraction
n is the ratio of the speed of light in a vacuum, c, to the speed of light in a material medium, v
n=c/v
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http://sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/light-and-sight/sci-media/images/refraction-of-light-in-water/685295-1-eng-NZ/Refraction-of-light-in-water.jpg
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Example
If a ray of light enters the glass-air boundary and if the n for glass is 1.52 and n for air is 1.0003, a) what will be the path of light? Create a diagram and label the media; b) in which medium will the light ray travel faster?
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https://upload.wikimedia.org/wikipedia/commons/8/85/Refraction_photo.png
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http://sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/light-and-sight/sci-media/video/refraction/668954-1-eng-NZ/Refraction.jpg
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Dispersion
Speed of light in a material in different substances is
different for different wavelengths
The index of refraction of a
material depends on wavelength
The dependence of wave speed and index of refraction
on wavelength is called dispersion
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In most material, n inc with decreasing wavelength and inc f
Light of longer wavelength has greater v than light of shorter wavelength
In the visible light in a prism, violet light is deviated most and red light is deviated least
Light spreads out and it is said to be dispersed into a spectrum
Dispersion
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DispersionThe amount of
dispersion depends on the difference between the
refractive indexes for violet light and for red
lighthttp://bolvan.ph.utexas.edu/~vadim/Classes/2014f/Prism1.jpg
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the science of color
ROYGBIV
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Basic Color Principles
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Color dimensions
vary
Color dimensions
vary
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Additive Primary Colors
These three colors can approximate, through
selective mixture, all of the other colors.
BLUE
RED GREENW
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Secondary Colors
Each is placed between the two primaries that are mixed to produce itM C
Y
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Primary & Secondary Colors
Red Blue Magenta
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Primary & Secondary Colors
Red Green Yellow
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Primary & Secondary Colors
Green Blue Cyan
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SCATTERING OF LIGHTColors and the colors of the atmosphere
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Scattering of Light• The absorption and re-
radiation of light in a variety of directions is called scattering
• Scattering of light depends on λ
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Scattering of Light: Why the sky is blueThe intensity of light scattered from air molecules is inversely proportional to the fourth power of the λ
Intensity ratio for the 2 ends of the spectrum: (700nm/400nm)4= 9.4
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Scattering of Light: Why the sky is white
Clouds contain high concentration of water droplets
Light of all wavelengths are scattered out of the cloud, so the cloud looks white
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Scattering of Light: Why sunsets are red?
Light has to travel longer distance
A substantial fraction of the blue light is removed by scattering: W-B= Y or R