Re: pinhole Re: VanDeGraaf question

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Sat Apr 09 2005 - 14:17:17 PDT 

Message-Id: <l03110723be7df48e7c97@[192.168.112.132]>
Date: Sat, 9 Apr 2005 14:17:17 -0700
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Re:  VanDeGraaf question

I Think Roy has it exactly right.

The Van deGraaf is a capacitor, a sphere surrounded by an insulator.

It get's charged by the belt.

Each person in the chain is also a capacitor, a conducting cylinder of a
person surrounded by insulating air and underlain by insulating shoe
material.

Each person is also a resistor.

When all of the capacitors are touching the Van deGraaf they all charge up.

All will discharge when the teacher touches the water faucet.

So the first student feels the current stored in the Van deGraaf flowing
through him/her, the next student feels the Van deGraaf current plus the
current stored on the first student, the last teacher in the line feels the
van deGraaf plus all the other student capacitors.

If this model is correct, then a line of students with the end student
touching the faucet, and standing at the other end of the line is a
teacher next to but not touching the Van deGraaf. (The teacher should hold
a metal rod in his/her hand to avoid electroporation by the spark that will
happen next.) Touch the rod to the Van deGraaf. The charge will flow
through the teacher but some charge will remain on the teacher to charge
his/her capacitor up. The next student gets a lesser charge and so on to
the student next to the faucet who gets the least charge flow.

Paul D

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