PHYSICS 232 – CHAPTER 32 ELECTROMAGNETIC WAVES For a by ves88494

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									PHYSICS 232 – CHAPTER 32: ELECTROMAGNETIC WAVES

For a plane wave in vacuum,
                                                 1
                           E = cB      ,   c=√
                                                  o µo

E ⊥ B ⊥ (direction of propagation).

Sinusoidal plane wave traveling in the +x direction,
             E = Emax sin(ωt − kx),        B = Bmax sin(ωt − kx),
Poynting vector: Energy flow rate (power per unit area),
                                       1
                                 S=       E×B
                                       µo
Intensity (time average of Poynting vector)

               Emax Bmax   Emax 2   1                  o    2       1     2
        I= S =           =        =                        Emax =     o cEmax
                 2µo       2µo c    2                µo             2

Electromagnetic waves also carry momentum. The rate of transfer of momentum
per unit cross-section area is
                               1 dp  S  EB
                                    = =
                               A dt  c  µo c
Radiation pressure:
                      prad = I/c    (absorbing surface)

                      prad = 2I/c     (reflecting surface)

								
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