Re: Pacmakers and Tesla coils = bad??
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Monday, February 14, 2000 4:24 PM
Subject: RE: Pacmakers and Tesla coils = bad??
>Original Poster: "Viggy" <LittleViggy-at-alum.manhattan.edu>
>It was my impression that EM fields, like gravitational fields; dropped
>off inversely proportional to the distance squared? I.e. the field at a
>distance 'd' away is equal to the field at "zero" distance, times
Only for a "point source", and in the "far field" for time varying fields.
For static fields, it goes as 1/r for an infinite line source, and doesn't
vary at all for an infinite plane. For time varying fields, it is a bit
more complex, because it takes time for the field from a given charged point
to "travel" to the measurement point. The "far field" can be loosely be
defined as far enough so that the source can be considered as a point
source. In practice, in antenna work, we consider distances that are
several wavelengths away from an antenna that is a fraction of a wavelength
in size to be reasonably far field.
For tesla coils, in general, the frequency is several hundred kHz, and a
wavelength is on the order of 1000 meters, so you're not going to be getting
several wavelengths away. However, the source is also very small (on the
order of 1/1000 wavelength) so for distances on the order of several times
the size of the source, you probably can consider it a point source.