Energy in EM wave

  • Thread starter Hydr0matic
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  • #1
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The reason the energy density of an EM wave is proportional only to the amplitude squared is because electromagnetic energy density U is:

U = (E2 + B2)/2

in units where c = μ0 = ε0 = 1

The average value of E2 is proportional to Emax2, it doesn't matter how fast E is varying, so the average energy density doesn't depend on ω.

Hurkyl

The electric field is also proportional to the acceleration of the charge. The larger the acceleration, the larger is the field.
-> http://electron9.phys.utk.edu/optics421/modules/m1/production.htm [Broken]

Hmmm.... If U ∝ E2, E ∝ a and a ∝ ω, how can Uavg not be dependent on ω ?
 
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Answers and Replies

  • #2
Integral
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I believe that the key word here is AVERAGE.
 
  • #3
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Why ? If Emax depends on ω, then so should Uavg.
 
  • #4
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Have I missunderstood something ? Will the amplitude of E increase when the oscillating charge accelerates faster ?
 

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