Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 55)

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Connect the wires according to the Wiring Checklist.
Initially the two loose wires are unconnected so there is
no sound. Now touch each wire with fingers from
different hands, you should hear a low-frequency sound.
(Wetting your fingers with water or saliva will make better
electrical contact). You are using your body as an
electrical component, just as you did in Experiment 19
(Finger Touch Lamp). If you like you may make the sound
louder by removing the wire from spring 18 (trans base)
and connecting it to spring 42 (3.3K
Ω), then connect a
wire from spring 43 (3.3K
Ω) to spring 18.
Now take a small cup (make sure it isn’t made of metal),
fill it half way with water, and place the two wires into the
water but without touching each other. The sound will
now have a much higher frequency because your
drinking water has lower resistance than your body. Now,
with the wires still in the water making noise, add some
table salt to the water and stir to dissolve the salt. You
should hear the frequency increase as you do this.
This circuit makes a good water detector. You could use
it as a warning alarm in case your house starts to flood
during a storm. Or you could use the frequency of the
sound as a water saltiness indicator.
You can also make a water kazoo. Pour a small amount
of water on a table or the floor and spread it with your
finger into a long line. Place one of the wires at one end
and slide the other along the water. You should get an
effect just like the kazoo you drew with the pencil, though
the frequency will probably be different.
You’ve seen how adding salt to water decreases its
resistance. So would it surprise you to know that pure
water (distilled water) has very high resistance? The
drinking water you are using here has small amounts of
minerals in it, which decrease its resistance just like salt
does. Your body conducts electricity because your body
is mostly water, with many things mixed in. When salt
dissolves in water it breaks up into particles called ions,
which are electrically charged. The ions make it easier
for electrons to travel through the water, similar to how
adding impurities makes it easier for electrons to flow
through semiconductors. Their overall effect is that the
resistance of the water is reduced. If you have some
distilled water in your house, try using it with this test.
EXPERIMENT #37: Fun with Water
Wiring Checklist:
o 19-to-25
o 5-to-21
o 6-to-22
o 20-to-26
o 23-to-32-to-unconnected
(the unconnected wire
should be long)
o 18-to-33-to-44
o 45-to-unconnected (the
unconnected wire should
be long)
o 27-to-24
Schematic
Long Wires to Water