metr 415/715 monday 2/4/2013. em radiation can be considered as particles as well as waves small...
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METR 415/715
Monday 2/4/2013
EM Radiation can be considered as particles as well as waves
• Small “packets” ot EM radiation that behave like particles
• Called “photons”
• E= Energy carried by photon• h= Planck’s constant = 6.626 X 10-34 J s• ν = Frequency
Photon’s are “indivisible”
• As text states on page 31 “very low intensity light deposits discrete packets of energy on a surface in a manner analogous to the occasional random splashes of fat raindrops on your windshield”
• If monochromatic radiation of wavelegth λ deposits F Watts per unit area on a surface, then this corresponds to F/hν photons per unit area per unit time
Flux (F)
• Flux is the rate at which radiation is incident on, or passes through a flat surface
• Expressed in units of Wm-2 for “broadband” radiation (radiation of many wavelengths)
• The flat surface may be oriented in any direction
• Monochromatic flux (Fλ) has units of Wm-2 per unit wavelength, Wm-2μm-1
Broadband Flux
• Encompasses a range of wavelengths. Defined as
Intensity
• Tells you in detail both the strength and the direction of various sources contributing to the incident flux on a surface
• Spherical coordinates are useful in describing intensity
• Coordinates are Φ (azimuth) and θ (elevation)
Solid angle
• Measured in steradians (sr)• Steradian – (ratio of area in a solid angle
compared to the area of a sphere of unit radius) 4π r2, where r=1
• In differential form, a steradian would be:
Reflection refraction scattering
Refraction of light in a raindrop
Scattering
Reflectivity of water
Absorption
• “Imaginary” part of the index of refraction• Gives you information on how much
absorption will take place
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