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 = X 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 (F λ ) has units of Wm -2 per unit wavelength, Wm -2 μm -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 r 2, 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