Fill container with water until pump
intake is submerged. Adjust flow so that water breaks into droplets
before reaching top cans. Neon bulb should light periodically and spark
should jump gap between balls.
NOTES
This is ordinarily used in the display
case. Here is the text that goes with it:
Notice how the two cans into which
the streams of water fall are cross-connected to the two tubes. Assume
that the can on the right becomes slightly charged when a stray ion in the
air sticks to it. The left tube becomes charged since it is connected
to the can. A charge of opposite sign is induced on the water stream
above the tube. When the water separates from the stream, it carries
this charge down into the left-hand can below and charges it and the right-hand
tube. The result is that the two tubes acquire charges of opposite sign
and induce opposite charges on the two streams of water, thus building up
the charges on the tubes until the electric field between the two metal spheres
is strong enough to cause breakdown of the air so that a spark jumps and
the discharge current lights the neon bulb. The entire process then
begins again. Potential differences of thousands of volts can easily
be produced this way. This is a beautiful example of the action of
positive feedback.
