Tips and Tricks for Electrostatic Experimenters
Foil- Be aware that there
are sources of metal foil besides commonly available kitchen foil.
Some metallic gift wrapping papers are really nice to work
with because they have a paper backing. It makes them easy to cut and handle,
and especially nice to glue to things.
Chocolate bars often have paper backed foil wrappers. It's
a good excuse to go get one.
The metallic Mylar (plastic film) that balloons are made
of, and some foods are packaged in, conducts electricity. While writing
this page I made a flat plate capacitor out of a CD case and scraps from
a potato chip bag . Yep, it works.
There are at least three types of metal foil tape that I
have seen. They are all used to work on duct work or insulation. I am NOT
talking about silver duct tape, however. Foil tape is exactly that, metal
foil with an adhesive backing. The three types I have seen are:
The aluminum soda cans are made from is thin enough to be
easily worked with. Its edges are sharp, however, and can cut skin deeply,
so be careful when using this material. Soda cans also have a coating on
them that may have to be removed.
While it is much thicker than foil, thin aluminum flashing
(used for roofing) can be cut with heavy duty scissors. Its thickness is
good for projects where structural integrity is required.
shapes are common to electrostatic devices for a couple of reasons. One
is that the "rounder" a shape is, the less it will leak charge into the
air or onto nearby objects. Another is that the larger the radius of a
charged sphere, the longer the spark is that can be drawn from it. Some
sources for conductive spheres:
A heavy duty foil with a sticky adhesive backing, made both
2" and 2-1/2" wide.
A very thin metal foil, backed by paper containing fibers
or string for strength, which is in turn backed with an adhesive. Made
in 3" width.
A tape the same as #2 except that the adhesive is on the
foil side instead of the paper side.
Plastic- Not all plastics are created equal. In
your research you may see a table or list of materials and their "dielectric
constant". The dielectric constant is a reference for how good an insulator
something is. Different plastics have different dielectric constants. The
other reference you may want to be aware of is "breakdown voltage". Breakdown
voltage is the voltage required for electricity to puncture a given thickness
of a given material. I recently made a Leyden jar out of a plastic soda
bottle and was disappointed to find that its capacitance was much lower
than expected. It would charge to a point, then partially discharge itself
through the plastic (this is a different phenomenon than spark over, which
is when a visible spark travels over the edge of a Leyden jar). When it
comes to building up a charge on plastic, these two references help explain
why things behave the way they do. Take a look at a variety of plastic
containers and try to find the letters that identify what kind of plastic
they are made from. You may see PTFE, PVC, HDPE, PP, PETE, or something
else. These initials stand for the name of the plastic. So far I favor
HDPE (stands for high density polyethylene) for making Leyden jars. PVC
is great for charging by rubbing.
Cabinet knobs. There are many varieties, the rounder and
smoother, the better. Be aware that some knobs may be round but have sharp
edges near their base. This may not disqualify them for use, but could
be a deciding factor if you have several to choose from.
Doorknobs. I have seen some beautiful spherical doorknobs.
The kind for closet doors or so called "dummy" knobs have no keyhole. Some
of them have a coating that may need to be removed.
Flag pole dealers. I know this sounds weird, but if you
start looking at flag poles you'll see that many have a beautiful metal
sphere on top. Yes, you can buy those spheres (in various sizes and colors).
They are often mounted on a threaded rod.
Copper plumbing floats. I'm not talking about the cheap
floats with crimped edges that are so common, but about smooth spherical
floats with a nut soldered on the bottom. They're made of two halves soldered
together and that joint needs to be smoothed out. They're also relatively
Plastic spheres. You can make plastic spheres into conductors
by coating them with india ink (get the real thing) or powdered graphite.
So far ping pong balls and fishing bobbers are my favorite. The bobbers
require sanding with very very fine sand paper to help the graphite or
ink adhere and to smooth out seams. Be warned that these will behave similar
to, but not exactly like a metal sphere. They seem to leak charge a little
easier. On a Leyden jar they sometimes produce a very weak spark if the
ball is too big in proportion to the jar. Another way to produce a conductive
sphere out of a plastic ball is to cover it with foil tape. Keep it as
neat as possible and avoid wrinkles as much as you can.
Glass- I personally
don't use glass very often, because plastic is cheaper and doesn't break
when you drop it. If you do use glass though, be aware that it can have
different dielectric constants too. Pyrex glass is different than plate
glass, which may be different than the jar your mayonnaise comes in.
Wax- Occasionally I have seen references to
waxing surfaces that are to be charged by rubbing. The idea is that you
polish some car wax, or paste wax on PVC and it helps to make a stronger
charge with less effort. My own experience has been annoyingly inconclusive.
I put carnuba wax on a sheet of acrylic and now I can't seem to put
a charge on it at all. I have put car wax on PVC and had mixed results.
In one case out of many, there was a noticeable improvement with respect
to the effort it took to create a charge. If you want to try this, do tests
before waxing your favorite piece of plastic. My best results have been
with liquid car wax.
Other Stuff- You may look at things a little
differently after you get into experimenting with electricity. A soda can
suddenly becomes ripe with possibilities. One
person uses them for the spheres on his Van De Graaf generators. A
disposable aluminum pie plate and a foam plate can be fashioned
into an electrophorus without much trouble. If you take this same idea
and use a sheet of acrylic or PVC you can get even
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