Basics of Radiation Physics How Heat Can Travel Through the Vacuum of Space How Radiation Affects Heat Here on Earth
Wavelength vs. Frequency λν = c Lambda*nu = C wavelength*frequency = speed of light C = 3.00 x 108 m/s (in a vacuum)
Example 1 λν = c Frequency of green light? Wavelength 500 nm = 5 x 10-7 m ν = c/ λ= (3x108 m/s)/(5 x 10-7m) = 6 x1014 s-1 1 s-1 = 1/(2π) Hertz (cycles/sec) ω = 3800 GHz
Example 2 λν= c Wavelength of FM radio waves? Frequency 103 MHz 1 s-1 = 1/(2π) Hertz λ = c/ν = (3x108 m/s)/(1.6x107 s-1) = 18.3 meters (!)
Planck Relation E = hν E = 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?
Comparative Latitudes of 4 US Cities • Fairbanks, AK • Ithaca, NY • Madison, WI • Honolulu, HI