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Re: Ice-pail experiment



On Sat, 25 Mar 2000, Savinainen Antti wrote:

Why the positive charge is totally on the outer surface after the metal
ball has touched the inner surface (the ball and the inner surface will
be neutral)? Wouldn’t it make more space for the charges that repel each
other if they were distributed both to the inner and the outer surface?


The same reasoning could lead us to suppose that the excess charge should
distribute itself THROUGHOUT THE METAL, since there is less room on the
surface. Wouldn't the mutual repulsion of net-charge on the surface cause
some of the net-charge to be pushed below the surface? If you answer
that, then you also answer why no net charge exists inside the hollow
cavity. The entire surface of the hollow cavity is "below" the outer
surface of the sphere.

Another possible problem: do your students imagine that the charge FLOWS
only on the surface? It does not. It flows through the bulk of tthe
metal. If there are surface net-charges inside the hollow chamber, then
they will repel each other OUTWARDS through the metal to appear on the
outer surface. The negative curvature of the inner surface causes any
excess charge to go DOWN into the metal, only to later appear on the outer
surface.

More thought-experiments:

Below, if this is a metal object with a "spike" attached to the inner
surface, and if we give this object an electrostatic net-charge, does the
charge at point "a" have a large value? No, it is zero.

OO OO
OO a OO
OO O OO
OO O OO
OO O OO
OOOOOOO



But in the diagram below, the surface net charge at point "a" is
significant. By making the spike slightly longer, the charge at "a"
changes greatly.

OO a OO
OO O OO
OO O OO
OO O OO
OO O OO
OOOOOOO



And in this diagram, the charge on point "a" is even larger. It probably
creates a corona discharge. Yet it is connected to the INSIDE of the ice
pail. Weird!

a
O
O
OO O OO
OO O OO
OO O OO
OO O OO
OO O OO
OOOOOOO

((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://www.amasci.com
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