Electrostatics

John J. Miller                 Maine East High School
                               2601 Dempster
                               Park Ridge IL 60068
                               (708)825-4484

Objectives:

Although this lab is based on the lab I perform with my high school sophomores, 
it has been adapted for the use for grade school. It works best in dry weather 
such as winter.  This is a set of mini-labs designed to be inexpensive (a set 
can be made for less than $2.00) so that the equipment can be put in the 
student's hands and explored.  If you are interested in a complete write-up with 
pictures or have a question, please call me. 
             
Materials Needed:

Plastic Tube (like PVC pipe or golf club tubes)
tiny scraps of paper
Scotch Magic tape
a piece of cloth like wool or fur
Styrofoam square 1' x 1'
A pie-tin with a styrofoam cup glued to the center (hot glued works best)

Strategy:

1. Have the students bring the end of the rod near the bits of paper. (the small 
   bits of paper should not attract to the rod). 

2. Have the students rub the plastics rod with the cloth and bring it near the 
   scraps of paper and observe what happens.  (The bits of paper should attract 
   to the tube where it was rubbed.)  Introduce the term "neutral" and 
   "charged".  We will say that something is neutral if it does not attract tiny 
   bits of paper.  We will call something charged if it attracts tiny bits of 
   paper. 

3. Now have the students bring the end of the rod that they did not rub near the 
   pieces of plastic.  (The small bits of paper should not attract to the rod 
   where it was not rubbed.)  Note: This is because the plastic is an insulator 
   which does not let the rubbed on charge freely flow. 

4. Have the students try rubbing other objects around the room (a comb, a pen, 
   or whatever) to see which ones can hold a charge.  (answers vary) 

5. Have the students take about 15 cm (6 inches) of the scotch tape and fold the 
   first few cm of each end sticky side together.  Have them stick the sticky 
   end down on a tabletop.  Now peel the tape up quickly.  Bring the tape near 
   the small bits of paper.  Is the tape charged?  (it should be) 

6. Have the students make another tape just like the first and bring it near the 
   other tape where both tapes are free to swing.  What happens?  (they should 
   repel) 


7. Have the students make two new pieces of tape like before but this time have 
   the students place the first one sticky side down.  Have the students now 
   place the second tape on top of the first and press down.  Peel the two tapes 
   up together THEN separate them.  Bring the two tapes near each other and free 
   to hang.  What happens?  (the tapes should attract) 

8. Have the students hang the two tapes freely from the side of the desk.  Re-
   rub the plastic tube and bring it near each tape.  What happens?  (The tube 
   should repel the tape that was on the bottom and attract the tape that was on 
   top.)  

Now is a good time to re-group and provide the students with some content.  
There are two types of charges, some attract and some repel.  Benjamin Franklin 
set the standard that when glass is rubbed with silk the glass becomes 
"positive" and when amber (a semi-precious stone) is rubbed with fur it becomes 
"negative."  This is where I ask students to take it on faith that the rod 
became "negative."  The rule for charges is opposites attract and likes repel so 
positive and positive repel, negative and negative repel and positive and 
negative attract.  The idea of the atom and positive protons and negative 
electrons may be also introduced along with the idea of electrically polarized.
(That explains why neutral objects attract to charged objects.) 

 9. Ask the students if the rod is negative and this tape repels, what must the 
    charge of the tape be?  (negative) 

10. Ask the students if the rod is negative and this other tape attracts, what 
    must the charge of the tape be?  (positive) 

11. Take the styrofoam and rub it with the cloth.  Place the pie-tin on the 
    styrofoam while holding it by the insulated handle.  Touch the metal (you 
    should get a small shock).  Lift the pie-tin by the insulated handle.  Now 
    touch the metal.  You should again get a shock.  This method of charging is 
    called "induction."  (When the pie-tin was near the negatively charged 
    styrofoam and you touched the metal with your hand, the negative charges 
    were repelled leaving the pie-tin positive.  When you picked up the pie-tin 
    by the handle it was positively charged.  When you touched it negatives from 
    your hand were attracted and entered the pie-tin making it neutral again. 

Performance Assessment:

Make a negatively charged tape by following the procedures in number 5.  Rub the 
styrofoam with the cloth.  Bring the styrofoam near the tape that is free to 
hang.  The tape should repel.  Ask the students, "What can we say about the two 
charges?"  (They are the same.  Really sharp students may say they are both 
negative.  That's good if they can back the statement with facts, not opinions.) 

Conclusion:

The conclusions have been placed after each question in parentheses. 

References:

Me. See above information