🚀 go-pugleaf

Sorry I can't quote the original poster's message---seems like I
pressed the wrong button this weekend...

Anyway, the question was why E and B fields are in phase in an EM wave
(in free space, away from charges, etc.)

The relevent Maxwell eqs. are:

	curl E + d/dt B = 0

	curl B - d/dt E = 0

in natural units (c=1).

From these we see that the _space derivative_ of B is equal to the
_time derivative_ of E (not E itself, if I recall the posted question
correctly).

Given that E & B are plane waves:

	E = E_0 exp{ i w (t - z) } x^
	B = B_0 exp{ i w (t - z) } y^

say, for a plane wave moving in the z^ direction, substitution into 
Maxwell's eqs. gives 

	E/B = 1  (really E/B = c, putting c back in)

So that B must follow E and vice versa.

--Jim


--
<>--------------------------------------------------------------------<>
      James E. Hetrick            Institute for Theoretical Physics
     hetrick@phys.uva.nl               University of Amsterdam