The enclosed animations were generated by a program I am developing 
called ElectriVUE.  ElectriVUE lets you create and display both still 
images and animations of the electric field and electric potential 
patterns associated with point electric charges.

The subject matter, of course, is physics, but I think the enclosed 
animations are fascinating to watch, and my non-physicist friends 
agree, so I decided to distribute them to a general audience.
(I know I risk losing 90% of you when I mention the "p" word, but
there WON'T be a test on this.  Think of this program as nothing more
than a screen saver.)

Efield.zip contains 3 animation files and an animation player that
displays these files on any PC equipped with at least 2 megabytes of 
extended memory and VGA graphics. (See the file "mustread." for a
description of how your extended memory manager MUST be configured
for proper playback.)

To run the program:

1) Follow the directions in "mustread." to ensure that you have enough
   extended memory AND file handles.
2) Type:    play    [Press Enter]
3) Press enter again to get a directory of the available animation files.
4) Use the up/down arrow keys to pick one of the three files.
   Start with "eandv.ani".
5) Press enter to load the selected file.
6) Press enter to load all 110 frames. (If you have less than 2 megabytes
   of memory, or less than 110 handles, try smaller numbers, starting with
   10 or 20.)
7) When the frames have all loaded (takes a few seconds), press enter
   twice to start the animation playback.
8) You can adjust playback speed by pressing:
   s -- to slow it down (probably necessary on fast PC's)
   f -- to make it faster (it starts at the maximum speed)
   space -- to freeze it
   Esc -- to exit  (press twice to completely exit the program).



What are you seeing?

Briefly... the 3 animations show what happens when electric charges
are brought in one pair at a time (from far away) to assemble two lines
of opposite charge.  That is, we start with no on screen charges, and 
one at a time a positive and negative charge move in to their final
locations.  The final configuration is 5 positive charges in a horizontal
line and 5 negative charges in a horizontal line below them.

Eonly.ani -- shows the evolving electric field lines as the charges move
             into place.
Vonly.ani -- shows the evolving electric potential (voltage) pattern in
             color.
EandV.ani -- superimposes the two patterns.

Electric field lines are often referred to as "lines of force" -- the
density of the lines (how tightly they are bunched together) at a 
particular point tells you how strong a force would be felt by any
ADDITIONAL electric charge (called a test charge) you placed at that 
point. The direction of the field lines tells you the direction of the
force felt by the test charge.  Electric field lines leave positive 
charges, and head towards negative ones (or off to infinity) so a 
positive test charge would be repelled from any positive charge in 
the pattern, and attracted by all negative ones.  The electric field
patterns seen here convey lots of information to a physicist, but you'd
have to learn more physics to understand it all...

The colored patterns are electric potential, otherwise known as voltage.
One way of describing potential is a measure of how much work you'd have 
to do to drag any ADDITIONAL electric charge (our "test charge") to any
specified spot.  The reason you'd have to do work is to fight the attraction
or repulsion of the charges already present in the pattern.  Rather than
filling the screen with 1000's of numbers describing the work necessary to
get to any given spot, I've assigned colors to different voltages.  If
2 points on the screen have the same color, they have the same voltage, 
which means that the TOTAL amount of work to drag any test charge in from
infinity to that spot is the same.

The electric field and the electric potential have a very close 
relationship.  You will notice that field lines are always perpendicular
to voltage (color) changes, and that fields lines are densest where the
colors change the most rapidly.


Alan Wolf
Assoc. Prof. of Physics
The Cooper Union

Comments to:  alan.wolf@factory.com
              aw@pipeline.com


