Re: How many joules --> e.m. waves?

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

On April 21, 1997 Brian Whatcott corrected a typing error and wrote:

> At a distance of lambda/(2.pi) units from an antenna radiating at a 
> wavelength of lambda units the magnitude of these two fields is the same. 
> By 16 wavelengths the induction has fallen to abt. 1% of radiation.

Thanks Brian for the correction; 84 pJ is even less than 84 nJ and this
reinforces the suspicion that a more efficient competnig mechanism may be 
at work. Induction (the transformer effect) is a very good candidate. Yes, 
I am in the near field. The wavelength for L=0.0028 mH and C=3000 pF is 
172 meters. At about 1 meter from the antenna the induced E may indeed be 
much higher than the noise.

I wish I had more time for additional experiments, for example, to use
an oscilloscope and to see how the induced amplitude changes with the 
distance from the source, x. For the induction effect it should go down 
as 1/(x^2+a^2)^1.5 (as B along the axis of a circular loop; a=radius).
Thus if the amplitude is 100 mV in the center of the loop it should 
become 60 mV at x=a, 18 mV at x=3*a, 6 mV at x=10*a, etc. A good student 
project, but not now (exams start in 3 weeks). Perhaps another Phys-L-er 
will investigate this topic experimentally and share the results. Then
we will know why we hear clicks from discharged capacitors.
                                                         Ludwik Kowalski