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Mercury Vapor Lamp and High Voltage
Name: Frank
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 1999-2001
Question:
Recently, I recorded on video an experiment using the
interior of a mercury vapor bulb. I induced 50,000 volts to the bulb to
see the reaction of the mercury vapor. Prior to applying the voltage, I
decreased the temperature of the bulb with liquid nitrogen in hopes of
keeping the mercury vapor cool from producing an illumination. My
finding after viewing the experiment on video tape was that it was
actually possible to see the increase of electron flow to the center of
the bulb, build a field, then collapse. What actually was I seeing? Was
I seeing the mercury vapor ignite? Or the electron flow?
Replies:
Frank,
You were probably seeing a corona discharge of electrons flowing between the
bulb's electrodes as electrons passed through whatever gas (a trace of
mercury,
nitrogen) might have been present inside the cooled tube.
Regards,
ProfHoff
I am not quite sure what you saw, but I can offer some suggestions as to
what you did not see in this VERY RISKY experiment.
1. How much current was involved in this 50,000 volts!! That could give you
a nasty, possibly lethal, jolt.
2. Cooling the mercury vapor discharge tube to liquid N2 temperature (77 K)
is also very risky. Those quartz tubes are not designed to withstand cooling
to such low temperatures. They are designed to withstand heating, because
the lamps get hot during normal operation.
3. At 77 K mercury is a solid, with essentially zero vapor pressure so you
could not observe a gaseous discharge that you would get under normal
operating temperatures.
There is not oxygen or other oxidant in those lamps, so the mercury vapor
couldn't ignite in the usual sense of the term.
4. With that voltage, it might be possible for the tube to conduct
electricity due to a microscopically thin layer of mercury metal deposited
on the walls of the discharge tube.
If you continue these experiments, prepare a "game plan" for a "worst
scenario" event --
the tube explodes, cracking the dewar containing the liquid N2, which in
turn implodes into sharp shards and shrapnel, showering toxic mercury
everywhere, that will be almost impossible to clean up. BE CAREFUL, you
are dealing with some significant hazards.
Vince Calder
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Update: February 2012
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