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sparks



I thought I'd found a really simple, down-to-earth real-life
example of the concept that fields carry energy, but now I'm
not so sure. Please tell me what you think.

When you unplug a high-power electrical applicance like a
halogen lamp or a space heater, you reliably get a big blue
spark between the plug and the light socket. When you plug it
back in, it seems like you sometimes -- but not always -- get
another spark.

I was interpreting this as the release of some of the energy stored
in the magnetic field in the space around the coil of the
step-down transformer where the power line feeds into my
house.

The other interpretation is that you simply create a strong
electric field in the air when the plug is close to, but not
quite touching, the socket.

Interpretation #2 alone can't explain the asymmetry between
plugging in and unplugging, which I'm pretty sure is real.
Interpretation #1 alone /can/ explain everything, but you
have to interpret the hard-to-reproduce sparks when
unplugging in terms of intermittent making and breaking
of the contact.

I'm guessing that both #1 and #2 are at work, but I'd appreciate
any comments. I worry because sparks are the kind of phenomenon
where it's hard to reproduce the effect, and things get pretty
subjective. Am I just fooling myself about the observed facts?

On a related note, does anyone know how strong a field is
required to ionize air, and how strongly this depends on
humidity?