RED AND GREEN "ELECTRICITY"

Here's a simple technique for demonstrating some basic electricity concepts. For classroom use, the colored shapes can be placed on an overhead projector. Also try using a white desktop, or a whiteboard. This demonstration is like an animated diagram, rather than a demonstration of any actual electrostatic effects. It is probably best used for grades five and above. I suspect that this demo is very effective for teaching basic electricity, because while I was working with these colored sheets, I discovered many new concepts myself, and I'm supposed to be an electricity expert! Therefore don't be shy in using these with adults as well as kids. By making "static electricity" visible, anyone can gain insights which we never had before.

You'll need some red plastic, green plastic, tape, and scissors. The colored film must be transparent if you intend to use it on an overhead projector. For use upon a desktop, translucent film is fine. I used some red and green clear plastic report covers from Fred Meyer stores. Larger sheets are available for about $8 as "filter gel" from theatrical supply stores. Ask for Primary Red and Primary Green filters.

Fig. 1 Red and green sheets stuck together, cut around the edge

First, let's make a model of ordinary matter:

• Roughly cut out a couple of red and green pieces, about 3" across.

• Place a bit of folded tape in the center of one sheet, sticky sides facing out.

• Stick the sheets together with the folded tape between them.

• Carefully cut around the edges so you end up with a perfectly overlapped BLACK shape, which is actually a sandwich containing red and green layers.

• Remove the tape.

Fig. 2 Matter is composed of positive (red) and negative (green)
in equal proportions

In everyday matter, the positive and negative charges are equal, so they cancel each other out, and the matter has an overall electric charge of zero. The plastic sheets illustrate this: when we combine the red and green, the result is colorless black. Normal "uncharged" matter is actually made of positive and negative charge, just as the black plastic sheet is actually made of bright red and green colors. Matter is entirely MADE of 'electricity', yet because the positives and negatives cancel out, we rarely encounter electrical effects in everyday life. Think about it: even our own bodies are made out of electric charge, yet it took mankind until the 1700's before we became curious enough to start seriously investigating electricity.

Make several more red/green cutout sandwiches of various shapes, so you have a collection of everyday "objects" with which to work. Or have your students make their own.

Fig. 3 Various everyday objects, all made with red and
green plastic sheets (and all made of opposite charge.)

DEMONSTRATE ELECTROSTATIC CHARGING

Fig. 4 Remove some green "negative" from your object.
This leaves behind some red "positive."

To tell the story of how "static electricity" can arise, touch a second black object against the one you have modified. Touch it only against the part of the object having the cut sliver of green. Use a finger to hold the sliver against this new object. This shows how one object can steal some "electricity" from the surface of another object.

Fig. 5 Here's how "static electricity" is caused by friction. It would be less misleading if
instead we said: "Here's how CHARGE SEPARATION is caused by CONTACT."

The demonstration above illustrates a number of distinct concepts:

• Conservation of Charge: separated positive and negative charges always appear in equal proportions when they are pulled from matter.

• Electron transfer: it's most often the green "negative" stuff that is exchanged between objects, not the red "positive" stuff.

• Existence of cancelled charge within matter: it shows that matter is actually made of vast quantities of positive and negative charge in near-perfect balance. It shows that charges are not CREATED, so much as SEPARATED and un-cancelled.

• The role of contact: it shows that charging arises through contact between surfaces, which implies that the surfaces must have had dissimilar electrical characteristics. (If the two objects in the above figure have identical composition, there would be no reason for one object to steal the green from the other.)

• We commonly state that "static electricity is caused by friction." This is not quite correct. While friction sometimes plays a secondary role in surface charging, its the contact and the electron-stealing which are the fundamental elements in the process. I try to avoid saying that "static electricity is caused by friction." It would be misleading. Instead I say: "charge imbalance is caused by contact and peeling!"

• A bit about the misleading label "static electricity"... What's being created here is not an invisible substance called "static." Instead, we are creating an imbalance between the quantities of negative and positive electrical "stuff" which were already there in the matter. Once they are separated, it's not necessary that the charges remain "static" upon the surfaces. The charge does not need to remain unmoving. It's not the static-ness of the charge which creates all the interesting effects, it's the imbalancing and separation of the plus and minus. Also, "Static electricity" is not the complement of "current electricity," since "imbalance" is not the opposite of "motion." Charge-flow and charge-imbalance are actually two different phenomena which can even occur together.

  How can "static" electricity flow? How can "static" and "current" be simultaneous? Easy: "static" is not static, it is imbalanced, and the imbalance can actually flow along. Is this a FLOW of STATIC electricity?!
  

  It would be less misleading if we called the imbalance by some other name besides "static." Maybe "Voltage electricity?" "Imbalanced electricity?"

DEMONSTRATE INDUCTIVE CHARGING

Fig. 6 CHARGING BY INDUCTION: the negative (green) object causes the
charges in the neutral ball to separate.

"STATIC" MEETS CURRENT

More Ideas:

MICROSCOPIC VIEW: Giant Atoms

In the center of one of the sheets draw a bunch of red dots spaced randomly 1/2" apart. Draw your "dots" large enough that the audience can easily see them when projected. These dots are protons or simple positive nuclei.

Now place your second transparent sheet over the first, align them perfectly, and draw one green dot on top of every single red dot. Make the green dots large enough so that the red and green overlap to produce black.

Now move the red and green dot sheets so that the dots only overlap partially. This illustrates induced dipoles, as well as piezoelectric charge separation. (When you squeeze a quartz crystal, the electrons and protons separate a bit, and opposite ends of the crystal will mysteriously display opposite charges.)

Now rotate the "green" sheet over the "red," and you've shown how a metal conductor operates, with the negative charge-sea able to flow along while every red metal atom still always has a green electron nearby.

Now rotate the "red" sheet and "green" sheet in opposite directions, and you've shown how electrolytic conductors (batteries and human bodies, for example,) can support electric current via opposite flows of positive and negative atoms. In salt water, electric current is made from moving sodium and chlorine ions, and no free electrons are present.

I admit it, I stole the above idea from Monty Python's "Holy Grail", where the hundred-eyed animated monster attacks our heroes in the caves. Crazily-swerving eyes, rather than nucleus-orbiting electrons.

SPIFFY SELF-ATTRACTIVE DYNAMIC FLUIDS

Fig. 7 CONDUCTOR DEMONSTRATION: Slope-sided bowls with the
lower half painted red

  \                                 /
    \      Side view of bowl      /
      \\                       //
        \\                   //  inside is 
          \\_______________//   painted red

Fig. 8 Fill both bowls with green water so the red part is exactly covered

Here's the simplest demonstration. Scoop some green water out of one bowl and dump it into the other. The bowl which has some green water missing now has a red border uncovered.

Fig. 9 To "Charge" a pair of metal objects, scoop some negative
green water from one "object" and drop it into the other.

INDUCTION: take one bowl, fill it with green water to cover the red. Now tilt the bowl.

Fig. 10 An electric field (tilted table) can slosh the negative liquid and
create areas of opposite charge on a conductor.

A SPREADING IMBALANCE: take one bowl, fill it with green water to cover the red paint. Now carefully pour some green water into the bowl from its edge, so the water runs down the tilted incline.

Fig. 11 Charge seems to spread instantly over the conductor, even
though it was deposited in one small place.

ELECTROMAGNETIC WAVES: take one bowl, fill it with green water to cover the red. Place it on a rickety table such as a portable card table. Now gently shake the table so that the green water in the bowl starts to slosh. See the alternating red and green areas? You are showing how an antenna can pick up electromagnetic energy. The moving table surface is an analogy for incoming EM waves. They make the electrons in your conductive object slosh back and forth, which creates an alternating current and an alternating plus/minus red/green charge signal. Wiggle the table too fast or very slow and the green water won't slosh. This shows how resonant frequencies are important with antennas: if you wiggle the table at exactly the right rate, you can build up a huge wave in the bowl.

RADIO TRANSMITTER: place the two bowls on a rickety card table. Fill them with green water to cover the red. Use a spoon to force the green water to slosh mightly in one bowl, and the sloshing bowl will shake the table, which can cause the other bowl to slosh a *tiny* bit.

CONDUCTORS AND INSULATORS: mix up some jello, color it green, fill one bowl with liquid jello-mix just enough to cover the red, then allow it to harden. Fill the other bowl with green water so you cover the red. You now have models of a conductive object (liquid) and an insulating object (solid.)

How is a conductor different than an insulator? In an insulator, the "green" charge does not flow when electric force is applied. In a conductor, when electric force is applied, the charges do start flowing. If you apply too much force to the jello (the insulator), cracks will shoot through the material and the green stuff suddenly moves for a moment, leaving a path of destruction. Jello-cracks are like electric sparks! Lightning happens when the "jello" in the air has "cracked" because of the strong electric forces in the space below the thundercloud.