The Electrophorus

My electrophorus is coming along quite well. I still
need to attach the acrylic plate to the base and attach
the handle to the metal plate but that shouldn't take to
long once I get the proper glue. I was able to test the
electrophorus with a makeshift metal plate made out
of aluminum foil attached to cardboard. It was a
success although the aluminum foil plate received
only a small charge. I hope the performance will
improve once I have a proper plate.

The electrophorus is made of a metal plate with an
insulating handle and an insulating material which
sits on a grounded metal plate. The electrophorus
is based on electrostatic induction.










To operate, the base is charged by frictional/contact
electrification.








For our purposes we will assume that
the base receives a negative charge.







After the base is charged the metal plate is placed on
top of the base and the negative charge repels the
electrons in the metal plate so that the negative
charge is furthest away from the base while the
positive charge is closest.









Next we ground the metal plate.










The metal plate has now been charged by electrostatic
induction.

The electrophorus is a valuable tool for demonstrating
the principle of electrostatic inductance. Electrostatic
induction is the basis for many electrostatic generators
such as the Wimshurst machine, the Dirod, and others.

For more information on the electrophorus check out:
http://en.wikipedia.org/wiki/Electrophorus
http://www.youtube.com/watch?v=w7A43NpbzYE&feature=related
http://www.ece.rochester.edu/~jones/demos/electrophorus.html
http://www.engr.uky.edu/~gedney/courses/ee468/expmnt/ephorus.html
http://www.alaska.net/~natnkell/electrophorus.htm

metal plate and handle












the base

Explorations in Electrostatics

Lately I've been intrigued by the topic of electrostatics. After
having performed several experiments and projects (one of
which was to build a miniature Van De Graaff machine)
I ordered two books Homemade Lightning by R. A. Ford
and Electrostatics A. D. Moore. Both were recommended
on Bill Beaty's wonderful amasci.com website.

Homemade lightning looks like a great book full of
information on electrostatic machines and accessories
as well as some accounts of strange phenomenon. The
other book has yet to arrive but it is supposed to contain
information on the theory of electrostatics as well as
information on building a dirod electrostatic generator.

My Van De Graaff generator was somewhat of a success.
It didn't obtain a very high voltage but it was capable of
causing small pieces of paper to dance up and down when
I waved my hand over the collector. It was quite fun to
play with and I do hope I can make a larger version eventually.

I proceeded to build a small Leyden jar capacitor using
instructions from this site. To charge the capacitor I waved it
across a TV screen that had just been turned on. This worked
quite well and produced 1/4 inch sparks. I also charged it by
rubbing PVC with a cloth.

More recently I started to try to build a miniature version of the
Wimshurst electrostatic machine from plans I found on
instructables.com. I don't fully understand how this machine
works yet but apparently there are many theories. Unlike the
Van De Graaff generator the Wimshurst is an induction or
influence machine while the VDG is based on frictional/contact
electrification.

I think my next step will be to read more about
inductance/influence machines and to build an
electrophorus.