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Re: [Phys-L] [Phys-l] Sparks

As noted below, old. Apparently no one replied to c. britton, so I'll venturer (being a fool).

Don't think so. The HV, as written. The conductor is atmosphere. While the LV is molten and vaporized?** metal. The spectrum will be very diff., and I suspect the I(V) will be diff. i.e. the gaseous will be non-ohmic (neg. resistance); if the metal is not gaseous, ohmic.***

** spectral analysis might reveal, also?
*** I -- V with a 'scope.


bc wishes he were an angel


p.s. This thread is peripheral to my claim that microwave mischief with a disk is of the low potential type, not a high V. spark. Repeating: If one uses low power the arcing, etc. is delayed. My interpretation is the delay time is while the Al heats up. I have an antique (haven't seen any for sale for some time) low power oven. I further delayed the arcing by adding load (glass(es) of water). Of course it may be a combination of the two.

On 2008, May 26, , at 08:19, chuck britton <cvbritton@embarqmail.com> wrote:

These low voltage, high current sparks are molten, burning droplets
of metal that follow parabolic trajectories.
Same as July 4 sparklers.

Is it right to compare these to high voltage, low current sparks
which are ionized atmosphere, plasma?
Miniature lightning bolts?


On May 25, 2008, at May 25(Sun) 9:29 , John Denker wrote:

Here's a fun experiment you can do.

Wear eye protection. Wear at least one rubber glove, unless you
trust yourself to adhere to the one-hand rule.

Start with a piece of stranded wire 4 or 5 cm long.

Unravel it to obtain the individual strands, thinner than a human
hair.

Bring in an automotive battery charger.
Set it on the "50 amp quick start" range.

Use it to zap the little wires.

The following assumes that one end of the wire is already
connected, and
we are about to connect to the other end:
*) I observe that if you approach the wire end-on you get a
bright spark
and the wire gets slightly shorter.
*) OTOH if you approach sideways, you can create a situation
where the
whole wire just disappears. I assume this is because you were
better
able to establish solid contact all at once.

This makes the point that high voltage is not needed to make rather
impressive sparks. People have the misconception that sparks are
associated with high voltage, perhaps because you need a high voltage
to strike an arc through /air/ ... but this experiment shows that if
you've got a big current through a small area, it will quite nicely
melt and/or vaporize metal.

If I am doing the work, I don't mind doing it without gloves, but
if students are doing it I might require them to wear at least one
glove. I've never actually seen anybody grab the un-insulated part
of the aligator clip, and after seeing how violent the sparks are,
some of them may not want to go near the insulated part, either.


----------

As a refinement, I find it convenient to put a dab of solder on the
stranded wire before unraveling it, so that the result is a brush
rather than a pile of little wires. Then I can hook up one solid
connection to the soldered end, and then zap the strands one by one.
The advantage is that this involves making N+1 connections rather
than 2N connections.

Also I find _combing_ to be quicker than trying to unwind the strands
one by one.

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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l