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Re: Displacement Current Revisited



Hi John,

> Original Poster: "John H. Couture" <COUTUREJH-at-worldnet.att-dot-net> 
> 
> 
>   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?

Firstly on induction vs EM fields: The only possible difference I can 
see would be a "near" return path for the antenna via ground (note 
the recommendations on optimum radial length - i.e. longer and they 
simply cost more). Otherwise ......... 

Secondly, on the circuit describe above: any circuit needs either a 
return path or a source and a sink. If one treats whatever is 
attached to each end of the tether as a capacitance one has a source 
an sink to the extent that they can charge up to what the generated 
EMF allows. If the negative one emits electrons and the other either 
gains electrons or emit positively charge ions one has a source and a 
sink.

>   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.

How do you detect a magnetic field oscillating at 100kHz or so with a 
compass?

Malcolm