Re: Magnetic Force with Tesla Coil?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Magnetic field can easily be computed using the peak current in the primary.

I^2 L = C V^2 and H = I /(2*pi*R) (approximation) for this case.  The
contribution from each turn could be added.  If a more accurate result is
wanted, one could use the differential current element to compute H.

Gerry R.

 > Original poster: davep-at-quik-dot-com
 >
 >
 >  >  > I have recently been thinking about the large magnetic field
 >  >> generated by a tesla coil,
 >     How large is it?
 >     Have you measured it?
 >
 >  >> and was puzzled by why a coil doesn't behave like a giant
 >  >> electromagnet as well?
 >     How do electromagnets at 100KHz (or whatever) behave?
 >      Hint 1) Compasses, etc ignore them.  Too Fast.
 >      Hint 2) maths (somewhat simplified) for mag field
 >      strenghts are current times turns.
 >        Primaries have few turns.
 >        Primary currents are low (in 'giant elemtromagnet'
 >        terms.) Such like deal in hundreds of amps of DC.
 >
 >  >> I mean, a large coil's primary can run at a
 >  >> considerable amount of power,
 >     cf as above.  mag fiekd depends on current, rather than power.
 >
 >  >> (I'm not just talking about pulsed power, I mean RMS as well) and
 >  >> it's field is great enough to light a flourescent tube
 >      Hint 3) Is this lit by _mag_ field or electrical?
 >      Hint 4) How large a field is required to do this?
 >
 >  >  > at a considerable distance, then why is there almost no attraction
 >  >> (at least, that I have heard of) on ferrous materials?
 >      As noted by others  frequencies are high, leading to inefficient
 >      attraction, mag fields such as they are fall of rapidly with
 >      distance, Also, mag fields are (in 'giant electromagnet' terms)
 >      relatively low.
 >
 >      (Story:
 >       I worked, briefly around a spot welder, doing EMI
 >       measurements.  Long time ago.   DC, 100s amps.
 >       THAT field would reach out and shake the electrons in the
 >       scope driving the display crazy...  8)>>)
 >
 > best
 >   dwp
 >
 >