Elenco Basic Electronic Experiments - Manual (Page 52)

EXPERIMENT #36: DRAWING RESISTORS
You need some more parts to do this experiment, so you’re going to draw them. Take a pencil (No. 2 lead is best but other
types will also work), SHARPEN IT, and fill in the 4 rectangles you see below. You will get better results if you place a
hard, flat surface between this page and the rest of this booklet while you are drawing. Press hard (but don’t rip the
paper) and fill in each several times to be sure you have a thick, even layer of pencil lead and try to avoid going out of
the boundaries.
Actually, your pencils aren’t made out of lead anymore (although we still call them “lead pencils”). The “lead” in your pencils
is really a form of carbon, the same material that resistors are made of. So the drawings you just made should act just like
the resistors in your Electronic Playground.
Connect the circuit, it’s the same basic oscillator circuit you have been using. Take the two loose wires and touch them to
opposite ends of the smallest rectangle you drew, you should hear a sound like an alarm. Note: you may get better
electrical contact between the wires and the drawings if you wet the wires with a few drops of water or saliva.
What kind of sound do you think you’ll get with the other drawings? (Hint: think about how resistors operate in series and
parallel combinations, or think in terms of the water pipes). Now touch the loose wires to opposite ends of the other
rectangles you drew (you may need to wet the wires again) and see if you were right. You can also slide one of the wires
along the drawing and see how the sound changes.
Making the drawn resistors longer should increase the resistance (resistors in series or longer water pipes) while making
them wider should reduce the resistance (resistors in parallel or larger water pipes). So all 4 rectangles should produce
the same sound, though you will see variations due to how thick and evenly you filled in the rectangles, and exactly where
you touch the wires. If your 4 shapes don’t sound similar then try improving your drawings.
Be sure to wash your hands after this test, unless you’re going on to Experiment 37 now.
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Shapes to be drawn.
Use a SHARP No. 2 pencil, draw on a
hard surface, press hard and fill in
several times for best results.