[SI-LIST] Re: how EM wave propagates through space
- From: Doug Brooks <dbrooks9@xxxxxxxxxxxxxxx>
- To: S A <shahbaz_assad@xxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
- Date: Tue, 04 Oct 2011 09:44:41 -0700
You might be confused by thinking about two different things (1) how
it starts, and (2) how it continues to propagate.
It does take moving charge to start an electromagnetic field. The
magnetic field starts at an antenna, or at some point in a circuit,
and radiates away from that point.
Once it starts to radiate away (propagate), it continues in a self
propagating manner. That is, the changing magnet field reinforces the
electric field, the changing electric field reinforces the magnet
field. Collectively, this is the electromagnetic field.
We are used to the concept of friction, and so intuitively we don't
think of this as continuing indefinitely. But in space, there is no
"friction,' or resistance, or power loss, The EM field just keeps
propagating forever. That is why we have antennas point out into
space hoping to hear signal from outer space generated who knows how long ago!
Doug Brooks
http://www.ultracad.com
At 02:38 AM 10/4/2011, S A wrote:
>Hi Experts,
>
>My question is related to propagation of EM waves.
>As EM waves have electric field and magnetic field and as we know
>that electric field is due to the motion of electrons and require
>some conducting medium.But I am confused that how EM wave propagate
>through space. what happens to the electric and magnetic field?
>I am sorry my question is very basic. but what happens to the
>electric and hence magnetic field in space and how these fields
>exists in space.
>
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>Thanks,
>Shahbaz Assad
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