🚀 go-pugleaf

Bob,

After reading the explanation so ably written by Don Simanek, I'm tempted to
keep silent, but...

I agree completely with Don.  The Mechanical Universe (High School
Adaptation) gives these analogies: the electric field is like the
gravitational force on, say, a ball on a hill side; it is down the slope in
the direction of maximum value; the electric potential is the height above
some point (sea level, the bottom of the hill, etc).  It is as if you climb a
hill (increasing the voltage, doing work against the field) and reach a
plateau, or a lake, which will be flat, no gravitational force in the
direction of motion, and therefore representing constant potential.  SO,
outside the Van de Graaff, the voltage is going (actually negative, since it
is being charged with electrons) up as points closer and closer to the dome
are considered.  But once inside the dome, the voltage is relatively constant
(high value, but constant), and the field is essentially zero, within
conditions mentioned by Don in his last paragraph.

Fun stuff.  It sure "turns on" the kids.

Larry