Re: First EM lab

[Brian McInnes <bmcinnes@PNC.COM.AU>]

on 14/1/02 5:44 PM, Bernard Cleyet at anngeorg@PACBELL.NET wrote:


> more direct than much physics these days (possibly more accurate than using an
> analytic balance -- the error will be in measuring the area of the piece of
> tissue)
> this method is considerably more accurate than using a micrometer for find the
> areal
> density of foils for radiation absorption expts.  -- or the thickness of gold
> leaf.
> for an electroscope.

> I've already given the formula for a "point" charge and a dipole, etc.
>
> bc
I'll pick up Bernard's latest contribution, as a convenient point.
Your formulas are correct and relevant.

The question of the mass of the paper is a bit of a non-issue!  Why not look
at the balance between the electric force on an individual carbon atomic
dipole (+4e and -4e) and the weight of the atom.

A lot of the discussion has been about estimating the charge on the pen
after it's rubbed through the hair.   The succession of questions about
charged sticky tape in the homework of C and S Chapter 1 goes like this:
1.  determine the number of excess electric charges on the surface of a
negatively charged tape.
2. find the fraction of surface molecules that have become charges when one
stick tape is stripped off another.
3. Compare this with the critical density of charge on the surface.
(critical in terms of triggering a spark in the air).


Brian McInnes