[EMAIL PROTECTED] wrote:
This is what I do not understand. The electric field is *not* an
electromagnetic field. It is a scalar field.
Here's a rather nice picture of a charged particle which accelerates,
and its associated field:
http://www.physicsinsights.org/images/mtw_moving_charge.png
The E field is not a scalar field. A scalar field is represented by a
single number (magnitude) at each point; the E field is represented by a
vector at each point (magnitude _and_ direction -- that requires 3
numbers in 3-space, or 4 numbers in 4-space).
So, in 3-space it's a vector field, not a scalar field. However, that's
not really a complete picture. It's actually just _part_ of the EM
field, and it doesn't transform indepedently of the B field. The E
field, alone, isn't a proper tensor field, and you can't predict how
it's going to look to various observers without taking account of the B
field as well. (The E and B fields together combine to form a rank 2
tensor which _does_ transform properly.)
You can also replace the E and B fields with the vector magnetic
potential, the "A" field, which is just a vector field, and which does
transform sensibly. In other words, the vector magnetic potential is a
tensor field.
For working with electromagnetic radiation it's necessary to take
account of both the E and the B fields. Furthermore, if you leave
special relativity out of the picture, it's very hard to make it work
out properly (SR was invented in large part just to deal with this sort
of problem, after all).
(I will just be leaving the picture up on the site for a few days --
it's scanned from MTW's textbook.)
-----Original Message-----
From: Stephen A. Lawrence
The information that the electron has moved is visible in the changes to
its field. Those changes propagate at C, just like any other EM wave.
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