Re: trying to understand/visualize EM waves. please help




"John Polasek" <jpolasek@xxxxxxxxxx> wrote in message
news:4qan16dac1brd2rgb4h9j1uq248tgson0o@xxxxxxxxxx
On Fri, 18 Jun 2010 10:14:17 -0400, "Bill Miller" <kt4ye@xxxxxxxxx>
wrote:


<snip>

You have stated the conditions correctly. But in order for E to cause H to
cause E...etc. It would be necessary for E and H to be out of phase. But
that would mean that the E/H ratio would have to be a complex number.

The impedance of space is 377 Ohm; not 377 +jX.
E and H are logically 180° out of phase which can be seen if E and H
are sine waves. Their operations are two derivatives apart, so that
the sine wave of one becomes -omega^2 sine of the other.
Simple analogy: voltage in a capacitor is time integral of current
1/Cint[idt, while the voltage in an inductor is the time derivative
of the current Ldi/dt, 2 derivatives ahead of the capacitor.
In AC parlance, Z = jwL and Z = 1/jwC and Z = R.
At resonance the sum of Z+Z equals 0.
Solve to find w^2 =1/LC.

Like Salmon Egg, you are lettting an inappropriate analogy get in the way.

Let's take your postulate that the electric field and the magnetic field are
180 degrees apart. Let us define the maximum electric field value as E and
the maximum magnetic field value as H. We agree that they are
time-synchronous. And they are both sine waves.

At time T_0, let us agree that E = 0 and H = 0. Now let us move forward in
time by 30 degrees in sine wave time. The electric field amplitude will be
0.5E and the magnetic field amplitude will be - 0.5E. Move forward in time
to 90 degrees. The electric field amplitude is now E and the magnetic field
amplitude is - H.

Question 1: If the electric field and themagnetic field are exchanging
energy, how is it that the energy contained in both the electric field and
the magnetic field have both increased simultaneously? Where did the energy
come from?

We can now proceed to time t advanced by 150 degrees. Now the electric
field magnitude has decrease to 0.5E and the magnetic field has decreased to
*0.5H.

Question 2: If the electric field and themagnetic field are exchanging
energy, how is it that the energy contained in both the electric field and
the magnetic field have both decreased simultaneously? Where did the energy
go?

All the best,

Bill




.



Relevant Pages

  • Re: Is electromagnetic field theory unified?
    ... Speed must change in order to energy be transmitted. ... You have refuted that torque must be present. ... >> stationary electric field. ... Observe the magnetic field placing any iron piece nearby. ...
    (sci.physics)
  • Re: Questions (Space)
    ... electric field lines as being red. ... so the magnetic field is called the "B field." ... In either the electric field or the magnetic field, energy is stored. ... The rate at which the alternation happens ...
    (rec.arts.sf.composition)
  • Re: fields and waves in the space
    ... Photons are known to originate as discreet and very minute quanta of energy. ... magnetic field produces an electric field. ...
    (sci.physics.relativity)
  • Re: Does a rotating electric dipole radiate?
    ... the rotational energy states are highly degenerate. ... referring to can be split using a magnetic field. ... am not sure the electric field will cause a change in energy of the ...
    (sci.physics)
  • Re: Does a rotating electric dipole radiate?
    ... has a certain symmetry you can say things about it that are valid both ... the rotational energy states are highly degenerate. ... referring to can be split using a magnetic field. ... Take the electric field in the z-direction. ...
    (sci.physics)