Basics of Radiation Physics
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Transcript of Basics of Radiation Physics
Basics of Radiation Physics
How Heat Can Travel Through the Vacuum of Space
How Radiation Affects Heat Here on Earth
EM Spectrum
Wavelength vs. Frequency
λν = cLambda*nu = C
wavelength*frequency = speed of light
C = 3.00 x 108 m/s (in a vacuum)
Example 1
λν = cFrequency of green light?
Wavelength 500 nm = 5 x 10-7 mν = c/ λ = (3x108 m/s)/(5 x 10-7 m)
= 6 x1014 s-1 1 s-1 = 1/(2π) Hertz (cycles/sec)
ω = 3800 GHz
Example 2
λν = cWavelength of FM radio waves?
Frequency 103 MHz1 s-1 = 1/(2π) Hertz
λ = c/ν = (3x108 m/s)/(1.6x107 s-1)= 18.3 meters (!)
Planck Relation
E = hνE = energy of one photon
h = Planck Constant= 6.63 x 10-34 J s Can also write:
E = hc/λ
Example: Energy of Green Photons
E = hc/λ
E = (6.6 x 10-34 J s)(3 x108 m/s)500 x 10-9 m
= 4.0 x 10-9 J/photon x 6.02 x 1023 photons/mole
= 2.4 x 105 J = 240 J/mole
Compare to Carbon Fixation
CO2 + H2O -> Glucose G = +120 kJ/mole
Light has energy of ~200 kJ/mole
Can visible light provide enough energy to fix carbon?
Stefan-Boltzmann Law
Black Cadillac vs. White Cadillac
Energy from Sun to Earth
Solar Angle
Solar Angle
Effect of Solar Angle on Radiation at the Surface of the Earth
Comparative Latitudes of 4 US Cities• Fairbanks, AK• Ithaca, NY• Madison, WI• Honolulu, HI
Sunlight Flux, cal/cm2/day
Local Solar Angle Effects