Elenco Basic Electronic Experiments - Manual (Page 56)

56
EXPERIMENT #39: FUN WITH WATER
Connect the circuit, 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 20 (Two Finger Touch
Lamp). If you like you may make the sound louder by replacing the wire between a23 and a31 with a 3.3k
Ω resistor
(actually this makes the circuit the same as the last experiment), though the tone of the sound will be different.
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.
LONG WIRES TO WATER
+9V
S
P
10k Ω
473