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Re: [Phys-L] transverse waves



Thank you again, John D.

My original topic was more limited.

I was thinking about a gravitational wave, traveling along the x axis, connecting two point-like masses, M (the source) and m (the receiver).

Perhaps someone, who teaches about E.M. fields (near different kinds of antennas) in a college-level course, will share his or her experience with us.


Thank you in advance,

Ludwik
===========================


On Apr 26, 2016, at 4:11 PM, John Denker wrote:

On 04/26/2016 06:50 AM, Ludwik Kowalski wrote:
I believe that electromagnetic waves are transverse, as far as
directions of their vectors E and B are concerned.

OK.

But they are
longitudinal, as far as their Poynting vector (W/m^2) is concerned.

That's not what is meant by longitudinal versus transverse.
Those terms apply to the ordinate of the wavefunction.

For example, for sound waves in a solid, or in a slinky, there
are both P waves and S waves, both longitudinal and transverse.
All of them carry energy in the direction of propagation, but
that's the answer to a different question.

========

Authors are free to define terms however they like, within
reason. However, there are limits.

-- Redefining what is meant by longitudinal versus transverse
makes no sense.

-- Redefining what is meant by radiation makes no sense.
There is a reactive field and a radiative field.
Please please let's not pretend that what's going on
in the reactive field is radiation. It just isn't.
The reactive field is real and has practical consequences and
is not transverse ... but it's not radiation.

===========================

Question: What's wrong with the following diagram:
http://www.kshitij-iitjee.com/Study/Physics/Part6/Chapter34/70.jpg
from
http://www.kshitij-iitjee.com/production-of-electromagnetic-waves-by-an-antenna

and similarly
https://en.wikipedia.org/wiki/Dipole_antenna#/media/File:Felder_um_Dipol.svg
and
https://en.wikipedia.org/wiki/Dipole_antenna#/media/File:Dipole_xmting_antenna_animation_4_408x318x150ms.gif
from
https://en.wikipedia.org/wiki/Dipole_antenna
and reused here
http://physics.stackexchange.com/questions/20331/understanding-the-diagrams-of-electromagnetic-waves

Given the amount of qualitatively wrong information out there, it's
a miracle that students ever understand anything.
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