Re: electroscope query (fwd)

From: Paul Doherty (pauld@exploratorium.edu)
Date: Tue Feb 10 2004 - 13:55:26 PST

Hi Ann Marie Grace

When I put two pieces of tape together in the air sticking the sticky side
of one to the smooth side of the other. The tapes start out uncharged.
(They have plenty of charges perhaps 10^20 plus and 10^20 minus charges but
the numbers are equal and so there is no net charge. When I pull the tapes
apart the sticky tape has a different stregnth of attraction for negative
charges than the smooth tape.

For Scotch magic tape the smooth side has a stronger attraction for
negatives than the sticky tape. So the sticky tape becomes positively
charged and the smooth side of the tape (in the inside part where the two
tapes touch) becomes negative.

The tapes start out neutral, for example one tape removes negatives leaving
the other positive.

When I pull a tape off a table it can become either plus or minus depending
on the material that the yop of the table is made of.

Paul D

>Here is an interesting one that I think you can answer.
>Thanks,
>Deb
>
>________________________
>Deb Hunt
>Snacktalk Moderator
>Exploratorium
>3601 Lyon Street
>San Francisco, CA 94123-1099
>dhunt@exploratorium.edu
>
>---------- Forwarded message ----------
>Date: Mon, 2 Feb 2004 18:06:14 -0500
>From: "amg@amgrace.com" <amg@amgrace.com>
>To: snacktalk@exploratorium.edu
>Subject: electroscope query
>
>Why does this work this way?
>
>I put a piece of tape on a table and another on top of it, sticky side to
>smooth side. I rip both pieces off the table and then rip them apart. The
>top piece is definitely negative and the bottom is definitely positive. Why
>is the bottom positive?
>
>When we put one piece of tape and rip it off the table we know it is
>negative because it has ripped electrons off the table. In the case of the
>tape sandwich, when you rip the top piece off the bottom it makes sense
>that it is negative since it is ripping off electrons. BUT why is the
>
>Why should we assume that some of the electrons from the bottom tape are
>removed along with excess electrons picked up from table?
>
>Any enlightenment will be welcome as soon as possible. Thanks!
>
>Anne Marie Grace & Susan English