Elenco Upgrade Kit SC500 to SC750 - Manual (Page 13)

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Use the same circuit as project #516. Take the two loose jumper wires
and touch them with your fingers. You should hear a low-frequency
sound. Now place the loose jumpers in a cup of water without them
touching each other. The sound will have a much higher frequency
because drinking water has lower resistance than your body. You can
change the sound by adding or removing water from the cup. If you
add salt to the water then you will notice the frequency increase,
because dissolving salt lowers the resistance of the water.
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 jumper 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.
Project #519
OBJECTIVE: To use water as a resistor.
Water Resistor
Project #520
OBJECTIVE: To make an adjustable low-frequency oscillator.
Build the circuit, turn on the slide switch (S1), and then press the press
switch (S2). Move the control lever of the adjustable resistor (RV) to
change the frequency.
Two-Transistor
Oscillator
To learn more about how circuits work, visit www.snapcircuits.net or page 85 to find out about our Student Guides.