3
Numerical Relationship between
 wavelength and photon energy
•Inverse relationship:  Smaller l means more energetic
–c = speed of light = 3.00 ´ 108 m/s
–h = Planck’s constant = 6.63 ´ 10-34 joule s
•Note:  Joule is a unit of energy        1 Joule/second = 1 Watt
•Energy of a single photon of 0.5 mm visible light?
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–Seems very small, but this is roughly the energy it takes to chemically modify a single molecule.
•Photons from a 100 W lightbulb  (assuming all 100W goes into light?)
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