# Lect23

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Unformatted text preview: Carry Energy Intensity Intensity = Average energy delivered per unit time, per unit area I≡ Length = c dt Length dt Area = A Area 1 dU A dt dU = u ⋅ volume = u Acdt I =c u Sunlight on Earth: I ~ 1000J/s/m2 1000J/s/m ~ 1 kW/m2 kW/m Waves Carry Energy Comment on Poynting Vector Comment on Poynting Vector Just another way to keep track of all this ­ Its magnitude is equal to I – Its direction is the direction of propagation of the wave Light has Momentum! If it has energy and its moving, then it also has momentum: Analogy from mechanics: For E&M waves: p2 E= 2m dE 2 p dp mv dp = = dt 2m dt m dt dE dU → = IA dt dt I P= c Radiation pressure = vF v→c IA = cF IF = cA pressure Preflight 4 60 50 40 30 20 10 0 But then again, what are we keeping constant here? WHAT...
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## This document was uploaded on 02/13/2014.

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