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Re: [Phys-l] Lissajous



On 08/30/09 14:57, chuck britton wrote:
Congrats on using 'real' instead of simulations.
A 60Hz 'wall wart' transformer can always be used for one (fixed)
frequency.

Fixed? Not really.

The long-term average frequency is very closely
controlled ... but there is a huge amount of
short-term frequency modulation.

In fact Lissajous patterns are a fine way of
exhibiting the modulation.

I strongly encourage doing this sort of experiment.

I have a book _Theory of Sound_ by some guy called
Rayleigh. The first few chapters give numerous
examples of nifty things you can do with Lissajous
patterns.

I spent many hours playing with Lissajous patterns
when I was in high school. I felt guilty about it
because it was too much fun ... and I had no idea
how useful it would be. It has paid off many times
since. Typical scenario: postdoc is trying to
figure out where the system is sitting relative to
some resonance(s). I set up the scope to display
displacement (or voltage) versus velocity (or current)
and everybody is amazed how well it works.

There are lots of XY tricks you can do with a scope
that don't exactly fit the definition of Lissajous
pattern. Classic examples include the transistor
curve tracer and the magnetic B/H tracer.

See:
http://www.ece.gatech.edu/research/labs/vc/graphics/devChar/trans.gif
which was taken from
http://www.ece.gatech.edu/research/labs/vc/processes/devChar.html

Also
http://www.vias.org/eltransformers/lee_electronic_transformers_09_10.html