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LightThe Nature and Colors of Light
The Electromagnetic Spectrum
Light waves are electromagnetic wavesLight waves consist of periodically changing electric
and magnetic fieldsProduced by accelerating charged particles
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
https://classconnection.s3.amazonaws.com/255/flashcards/4013255/jpg/electromagneticspectrum-141B490BAC872789434.jpg
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
Reflection
Wave changes direction upon hitting a
reflecting surface
0ri
R
N
I
R= reflecting rayr= angle of reflectionI= incident rayi= angle of incidenceN= normal
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
Refraction
Wave changes direction upon
entering a medium of different density
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
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
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?
https://upload.wikimedia.org/wikipedia/commons/8/85/Refraction_photo.png
http://sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/light-and-sight/sci-media/video/refraction/668954-1-eng-NZ/Refraction.jpg
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
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
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
the science of color
ROYGBIV
Basic Color Principles
Color dimensions
vary
Color dimensions
vary
Additive Primary Colors
These three colors can approximate, through
selective mixture, all of the other colors.
BLUE
RED GREENW
Secondary Colors
Each is placed between the two primaries that are mixed to produce itM C
Y
Primary & Secondary Colors
Red Blue Magenta
Primary & Secondary Colors
Red Green Yellow
Primary & Secondary Colors
Green Blue Cyan
SCATTERING OF LIGHTColors and the colors of the atmosphere
Scattering of Light• The absorption and re-
radiation of light in a variety of directions is called scattering
• Scattering of light depends on λ
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
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
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