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