Re: Do the peeks of an EM wave move forward or only up and down?


Tom Roberts wrote:
guskz@xxxxxxxxxxx wrote:
> If say the peeks of an EM wave are mountains:
> 1. Do these mountains move forward with time and remain the same
> distance apart (= frequency)?

For an infinite plane wave, yes.
But their distance apart is their
wavelength, not frequency. wavelength = c/frequency.

Such a wave traveling along the z axis is described mathematically:
I used to and prefer to use x as a horizontal traveling axis and y as
the vertical axis for the wave...


Ez = Bz = Ey = Bx = 0
Ex = E0 sin(w t - (w/c) z)
By = B0 cos(w t - (w/c) z)
w = 2 pi f, where f is the frequency of the wave.
Is w the angular velocity and how come the amplitude is not in the
equation, meaning w = 2pi A F

There is a relationship between E0 and B0 you can look
up; both are constant.

Since the peaks of cos(x) occur when x=2 n pi (n an integer), the wave
Ok, but the peaks travel all along the z axis, meaning at any variable
value along the z axis, correct?

is traveling in the +z direction.


> 2. Or do these mountains(wave peeks) remain in place and only move up
> and down with time?

No. But for water waves, the individual molecules of water do
(approximately) stay in one place horizontally and opnly move up and
down with time.

Are you sure, I thought that water waves created by a moving boat do
travel horizontally(I thought EM waves where the exception not water
waves) otherwise wouldn't a cork on these waves remain in the same
location (bopping up and down) instead of moving forward with the
waves?

For an EM wave, the E and B fields at a given point
oscillate between their max and min values; attempting to discuss a
field "moving" does not make sense.

I'm not sure what you mean, unless you mean an EM wave surrounding an
electron (oscillates around the electron) as it moves in a wire where
as I'm talking about for example about a Radio EM wave emitted by an
antenna (as the wave propagates away from the antenna)?




Tom Roberts

.

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