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Unformatted text preview: Carry Energy Intensity
Intensity = Average energy delivered per unit time, per unit area I≡ Length = c dt
dt Area = A
Area 1 dU
A dt dU = u ⋅ volume = u Acdt I =c u Sunlight on Earth:
I ~ 1000J/s/m2
~ 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
dE 2 p dp
dt 2m dt
m dt dE
Radiation pressure = vF
v→c IA = cF
cA pressure Preflight 4 60
0 But then again, what are we keeping constant here? WHAT...
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This document was uploaded on 02/13/2014.
- Spring '14