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45
Project #123 Sound Wave Magic
OBJECTIVE: To show how sound waves travel on a paper
surface.
Build the circuit shown on the left and connect the speaker (SP) using
the two (2) jumper wires. Then, lay the speaker on a at hard surface.
Setup: Use some paper and scissors to cut out a rectangular pattern.
Use the one shown below as a guide. Use colored paper if available.
Fold at the points shown. Scotch tape the corners so the tray has no
cracks at the corners. Place the tray over the speaker and sprinkle a
small amount of white table salt in the tray. There should be enough
salt to cover the bottom with a little space between each salt grain.
Sound Magic: Turn on the circuit by turning on the slide switch (S1).
Adjust the adjustable resistor (RV) for different pitches and watch the
salt particles. Particles that bounce high are directly over the vibrating
paper and ones that do not move are in the nodes where the paper is
not vibrating. Eventually, all the salt will move to the areas that have
no vibration, and stay there. Change the position of the tray and the
material used to create different patterns due to the sound. Try sugar
and coffee creamer, for example, to see if they move differently due to
the sound waves.
Paper Tray
Salt
Sample Cut-out Pattern
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