Re: Charge Distribution around pointed areas

[Robert A Cohen <bbq@ESU.EDU>]

I use the following demo: I ask four students to get up and, pretending
that there is a strong force of repulsion between them, move as far as
they can from each other.  Inevitably, they move to the four corners of
the room.  Adding more students will have all the students move to the
walls, but it is apparent that the corners are the "preferred" place to
be.

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| Robert Cohen               Department of Physics       |
|                            East Stroudsburg University |
| bbq@esu.edu                East Stroudsburg, PA  18301 |
| http://www.esu.edu/~bbq/   (570) 422-3428              |
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On Mon, 15 Nov 1999, David Strasburger-fac wrote:

> I'm not sure what kind of kids are in "Ontario grade 12A Physics" and so
> what type of explanation you are looking for.  A quantitative explanation
> was posted recently so I'll add the story I typically tell a conceptual
> class:
>
> Consider awkward fourteen-year-olds at a dance.  They try to stay away
> from eachother.  (Ok -- it's not the best analogy -- but let's just accept
> the story for the sake of having something to visualize.)  If the dance is
> held in a round room the kids will plaser themselves against the
> periphery, uniformly staying as far from eachother (and the dance floor)
> as possible.  If, however, the room is rectangular, the kids will have
> higher concentrations at the corners (not just because they're dark)
> because they make the following compromise: be closer to a few of their
> classmates in exchange for being farther from the majority.
>
> The analogy is flawed in a number of ways -- but it helps kids get a first
> picture.
>
> David Strasburger
> Noble and Greenough School
> Dedham MA
>
>
> ________________
> Date:    Sun, 14 Nov 1999 20:30:19 -0500
> From:    Brian Rintoul <Brian_Rintoul@OCCDSB.ON.CA>
> Subject: Charge Distribution around pointed areas
>
> I'm about to start my first time teaching the unit on Electricity, for the
> Ontario grade 12A Physics course, which opens with electrostatics.
>
> If a charged object is spherical, the charge is uniformly distributed over
> the surface, the reason for this distribution is quite clear.  What isn't
> immediately apparent, this Biochemist is, why charge becomes concentrated
> around sharp pointed areas on a conductor's surface.
>
> Explanation please.
>
> ______________