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Re: [Phys-l] phase relationship

Now I'm puzzled -- I for some time, erroniously?, thought E and M were in phase in "free" space**.


A dipole detects E while a loop detects M (B?)

X band freq. is convenient.




American Journal of Physics, Volume 39, Issue 1, pp. 121-122 (1971).



Or a twist of the wrist:


A probe of electromagnetic waves has been developed and employed forclassroom demonstrations of both standing electric waves and standing magnetic waves. By a "twist of the wrist" it was oriented to demonstrate the two waves independently. The field patterns were not appreciably altered by the probe since its dimensions were less than one-tenth wavelength.

©1957 American Association of Physics Teachers



http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000025000008000568000001&idtype=cvips&gifs=yes&ref=no

Wherein the nodes of E are at the same point as the antinodes of B. [standing waves]



** not in an absorbing media?



bc at a teachable moment.











On 2010, Mar 20, , at 06:08, Brian Whatcott wrote:

ludwik kowalski wrote:
OOPS,
I was not the author of the message. I deleted the author's name; my
name was added from the signature file.

Ludwik
/snip/

there's an error in your argument.
See

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35

for a graphic (you can pause the display by clicking inside it)
showing the correct phase relationship, or

http://en.wikipedia.org/wiki/Electromagnetic_radiation

for a detailed account -- the section 'properties' pictures the
correct phase relationships, and 'derivation' solves M's equations for
a general propagating wave, finishing with the equation relating E and
B which shows that they are in phase.
I have heard this statement before - and it conflicts with my mental model
of the process of propagation - say from a dipole.
It would be easy to observe whether the in-phase assertion is true:
for low frequency radio signals, (10kHz to 100kHz) the signal may be
observed
as an electric field, or as a magnetic field via suitable sensors to a
scope.

Brian W