Re: Questions (Space)

Ric Locke <warlocke@xxxxxxxxxxxx> wrote:
Tina Hall wrote:

If there's a problem, it's translating. Not English, but how you
understand it into something I understand. Guessing the right
analogies can be difficult (with all the years of us posting here
you still don't have the direct experience of teaching me something
and seeing the result face to face), some hit home, others just
confuse. So I try to add my own asking whether they're ok.

Ok, let's try it. Here goes --

One of the first useful things people found out about electricity and
magnetism is that they are connected. The connection is that if one
changes, it creates the other, and vice versa.

Changes?

I know that coils produce magnetism by electricity, but I don't know
_how_. I could only guess how you get electricity from magnets.

If we have a particle with an electric charge, an electron for
instance, there is a zone around it in which we can find out that
there's an electron nearby because we can detect the electricity.

Ok.

That area is called the "electric field". The usual way of depicting
it is lines going straight out from the electron, radially.

That's odd. (I'd put a circle around it.)

In three dimensions, much like a sea urchin or one of those fluffy
balls some people use for taking a bath.

Eh, no idea what you mean. :)

The lines aren't really there, mind you; the zone is homogeneous, but
thinking about it as lines is handy.

While to me a circle (or sphere) makes sense, and lines don't, as as you
say, they're not homogenous.

I think of electric field lines as being red. People often refer to it
as just the "E field."

Hm. To me they look blue. :)

Similarly, the zone around a magnet is a "magnetic field". "M" is
used for mass, so the magnetic field is called the "B field." (I
don't know why they used "B".) Like the electric field, it's commonly
depicted as lines; I think of them as blue.

I remember them depicted that way. Going from one pole to the other
round a bend.

Magnetic field lines are always a loop that goes back through the
magnet, while electric field lines are radial (important to know for
some things, but it doesn't matter here.)

Ok.

I also remember something about something going round in a certain
direction around an electric line. (If that has anything to do with
this, my mind vaguely says it's connected, mainly with coils.)

In either the electric field or the magnetic field, energy is stored.
I think of it as space being like a spring, or perhaps rubber -- it's
stretched or compressed, which stores energy.

I don't see that (would get a headache if I tried).

Start with a magnetic field and move away from the magnet, so all you
can see is blue lines. Pick a vertical one for now, and snip off a
bit of one line. Now you have a little bit of isolated magnetic
field, not connected to anything. It has a direction, say from bottom
to top (a little arrow point at the top might help; it does for me.)

Can't be, you say -- and you're absolutely right; that isolated
snippit can't exist without the magnet to keep it there. So it goes
away. The line becomes shorter and shorter until it winks out at a
point.

Huh?

(I just wondered why I would cut the thing. Never mind how it could stay
in existence. I'd think it's gone immediately. But why lines, anyway.
I'd be more comfortable with an area. Unless you say there's indeed
empty space between the lines. Because if there isn't, the lines
mislead.)

But the energy that was stored in that bit of magnetic field is still
there. It can't just vanish. It has to go into some other effect.
Where did it go?

I don't think we can go any further past the point I couldn't follow;
cutting a bit of magnetic something out. It looks like a cartoon figure
running off an edge and staying in the air before it drops. Nothing that
can actually happen; you can't cut out and hold that piece, so nothing
can happen with it if you did.

I'm stuck there, so I can't follow the rest. Sorry.

[...]

The alternating strong-and-weak of the electric and magnetic fields
is what is spoken of as "waves". The rate at which the alternation
happens is the "frequency". The speed of light, divided by the rate
of alternation, is the "wavelength". The whole system, of electric
field and magnetic field swapping energy, and the locus of that
exchange moving through space, is "electromagnetic radiation".

That might make sense if I knew where it came from, the piece cut out to
begin with. _Not_ as something cut out like from a cake, actually, but a
whole thing originating somewhere.

Just as I wondered where the photons come from. What makes them.

(No idea whether the two are connected.)

If there is a lot of energy in the system, the alternation happens
very fast so the wavelength is very small. If there is little energy
in the system, the alternation happens slowly and the wavelength is
large.

That's what photons, do? Swap back and forth between electric and
magnetic? (That would be two directions of strength even, except from
what I can guess from what I've seen posted in this thread, it's either
one or the other, not alternating. <sigh> I guess I have to live on
without brilliant insights into this. :) )

Radio doesn't have much energy, so the alternation only happens a few
times, up to a few million times, per second, and the wavelength comes
out to kilometers or meters.

You know, that way I can even picture a wave travelling around in 3D
space. (Which is an answer to a question elsewhere in this thread, not
what I was wondering about here.) Life's funny. :)

Light has a lot of energy, so the alternation of B and E field happens
billions of times per second and the wavelength is in micrometers. But
the same process happens in both effects -- the energy is stored in
electic field and magnetic field, alternately, as it travels through
space. That's why I said before that radio is cool and slow, while
light is hot and fast.

I'd prefer to drop the temperature, though, and just think of it as
strength (or amount of energy).

And of course you could just as well start with a snippit of electric
field, which would decay to produce a B field, which would decay to
make an E field... in fact, this is what a radio transmitter does. We
make an electric current flow in the antenna. This creates a bit of
isolated B field, which decays to form an E field, and so on.

Interesting, and something I can imagine. (Not that I get how you get a
current in something that just sticks out in the air with no 2nd
connection.)

There's much more, but is this bit useful and/or understandable?

Parts of it helped unexpectedly, while others just didn't work, and some
made sense as it is with the bits I picked up. Overall it was very nice
of you to explain this. Thanks. :)

--
Tina
WIP: Space: 1317 words
WISuspension: Seasons & Elements trilogy | Magic Earth series
Posted to Usenet newsgroup rec.arts.sf.composition.

.

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