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.
First, let's make a model of ordinary matter:
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
the 1700's before we became curious enough to start seriously
green plastic sheets (and all made of opposite charge.)
DEMONSTRATE ELECTROSTATIC CHARGINGCut a sliver out of the edge of the green part of one of your objects, while leaving the red sheet uncut. You now have a sliver made out of green "negative charge." You also have a black object that has a red stripe of "positive charge" on its edge.
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
instead we said: "Here's how CHARGE SEPARATION is caused by CONTACT."
The demonstration above illustrates a number of distinct concepts:
DEMONSTRATE INDUCTIVE CHARGINGPlace one of your "black" objects on the overhead projector. Place a small piece of green plastic on the overhead an inch away from it. Since alike charges repel, and green repels green, demonstrate this by slightly sliding the green part of your large "black" object away from the small green piece. Slide it just a tiny amount, just enough to expose some bands of color on the black object:
charges in the neutral ball to separate.
"STATIC" MEETS CURRENTCut out two perfect circles of red and green plastic. (It helps to use a compass to mark them.) Remove any tape, superimpose them upon the overhead projector green side up, place a pencil point against their exact centers as a pivot, then carefully rotate the green disk while leaving the red disk stationary. This demonstrates electric current. See any colors? No, since electric current is a flow of the *neutralized* charge within a metal. The green can flow through the red, yet the two colors remain mixed together. Now un-overlap the two disks a bit to expose some red/green colors and to demonstrate "static" electricity. Can you see the difference between "static" and "current?" "Static" is when the red and green (the plus and minus) is imbalanced. "Current" is when the red and green move relative to each other. Obviously "static" and "current" are not opposite kinds of electricity. Instead they are two independent phenomena. If your textbooks say that "static electricity" is the opposite of "current electricity," then they are propagating a misconception which must be UNlearned if students wish to make good progress in later understanding electrical science. An imbalance need not be "static", and an imbalance is not the opposite of a flow. In the same way, "static" electricity is not necessarily unmoving, and imbalanced charge is not the opposite of charge-flows.
More Ideas:Once the red/green plastic gets boring, you can put together some other demonstrations based on the same effect...
MICROSCOPIC VIEW: Giant AtomsTo crudely illustrate the nature of the red and green plastic analogy, I made an overhead projector demo which depicts the red and green atoms in the plastic. To do this you need two transparent, uncolored sheets, a red marker, and a green marker.
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
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
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.
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 FLUIDSIf electric charge was REALLY large and colored, we could do all sorts of visible demonstrations which show how electrostatic fields and forces work. The connections between electric fields and electric charge might then be intuitively obvious to students. Here's a way to accomplish this by using gravity fields and colored water.
lower half painted red
green water from one "object" and drop it into the other.
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.
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
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