ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
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Vera
Greetings from a co-presenter at the Phoenix ASTC conference. Hazel and I are still grateful to you for helping us make non-destructive, minimum dynamite choices among the restaurant hot sauces so casually ingested by inhabitants of the Southwest.
Here is an old-fashioned but rather simple way to demonstrate "conservation of electric charge", the idea that electric charges cannot be created or destroyed, but can be transferred from one object to another. The activity will show that if two objects are initially uncharged or neutral and they are rubbed together, one will usually take surface electrons from the other, and the quantity of electric charge one gains will exactly match the quantity of electric charge the other one loses, but they will have opposite kinds of charge, one positive and the other negative.
Apparatus needed:
---sensitive electroscope, typically gold leaf, with a hollow metal can mounted on its knob
---postage-stamp-size piece of fur or wool glued to one end of a pencil-sized clean and dry glass tube or rod
---small piece (about 20 mm long) broken off the end of a plastic or hard-rubber comb, glued to one end of a pencil-sized glass tube or rod, clean and dry. Use these glass rods as insulating handles for the comb and wool (or fur).
Initial understanding needed: that the gold leaf rises when an electrically-charged object is inserted into the metal can mounted on the electroscope's knob. The charged object should not touch the can, just be held inside it.
The activity:
1. Start with both the comb and the wool uncharged (neutral), as can be shown by inserting each one separately into the can and observing no rising of the gold leaf. If either should be charged it can effectively be neutralized by passing a lighted match underneath the comb and/or wool. (The copious supply of plus and minus ions in the heated air rising from the flame will supply whatever charge is needed to neutralize the comb or wool....remember, opposite charges attract. The ions are produced by neutral molecules colliding vigorously enough at high temperature to knock electrons off each other.)
2. Holding them outside the can, rub the comb and wool on each other.
3. Insert the comb fragment into (but not touching) the can on the electroscope. If it is charged, as it usually has become, the gold leaf will rise a certain distance and stay there as long as the charged comb is inside the can.
4. Take out the comb fragment and insert the wool or fur. It should also be charged, and the gold leaf should rise just as far as it did with the comb.
5. To show that these two charged objects, the comb and the wool (or fur), have equal amounts of charge but one is positive and the other is negative, is to put one inside the can (leaf rises) and then also insert the other. The leaf should fall to its original uncharged position, hanging limply down. Taking either one out and leaving the other in causes leaf to rise.
With the proper theatrical treatment by a dramatic presenter, the marvel of step 5 can be made quite impressive.
Enjoy.
Al Read, Director, Science Discovery Center of Oneonta (NY)
-----Original Message-----
From: Informal Science Education Network on behalf of Vera Uyehara
Sent: Sun 11/7/2004 9:13 PM
To: [log in to unmask]
Subject: Conservation of Electricity exhibits
ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************
Has anyone seen an exhibit on the conservation of electricity? If yes, what
components did it include? V
Vera L.Y. Uyehara, President
Quantum-Itch, Inc.
"Learning for a New Millennium"
5557 North Maria Drive
Tucson, Arizona 85704
(520) 408-1312 Voice and Fax
(520) 270-5265 Cell
[log in to unmask]
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More information about the Informal Science Education Network and the
Association of Science-Technology Centers may be found at http://www.astc.org.
To remove your e-mail address from the ISEN-ASTC-L list, send the
message SIGNOFF ISEN-ASTC-L in the BODY of a message to
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