Re: Displacement Current Revisited

  Malcolm -

  I agree that the far field or electromagnetic field (Hertz) was what
energized your LED's.

  However, near the radio transmitter antenna there is also another field
that Terman in his Radio Engineers' Handbook called the induction field
(Faraday). This induction field reduces rapidly in strength with distance
and is negligible a short distance from the antenna or Tesla coil unlike the
EM field which reduces as the square of the distance.

  Terman says that the induction field is stronger than the EM field near
the antenna. I would expect that Reinhart's 25 watt lamp and wire antenna
near the Tesla coil was energized by the induction field. However, Reinhart
points out this was not a closed circuit, or was it? Note that the space
shuttle tether system appears not to be a closed circuit but actually it is.
Can you explain this circuit?

  Coilers are apparently not familiar with the induction field around the
Tesla coil. If I understand this field correctly a coiler should be able to
detect the field with a compass placed near a TC while it is energized. The
compass is not sensitive to the EM field but should deflect because of the
magnetic effect of the induction field. The compass would have to be
properly aligned and very close to the center of the secondary winding. Has
anyone tried this test? Reinhart's lamp could be used but this is also
sensitive to the EM field.

  John Couture


At 05:38 PM 3/18/99 -0700, you wrote:
>Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> 
>Hi John,
>>   Is it correct that Malcolm's LED's were energized by the far fields and
>> Bart's lamps were energized by the near fields. How can you prove this?   
>According to the formal definition of near and far fields given by 
>someone else, my LEDs are being lit by received far fields. 
>Personally I cannot understand on what grounds a distinction is being 
>made other than it has a bearing on what the antenna "sees" as its 
>load. I can't see that it makes any difference to laws governing 
>received power as distance from the antenna is changed.