PURPOSE: To demonstrate the separation of electric charge.
DESCRIPTION: Rub an acrylic rod with a paper towel to get a positive charge. Rub a pvc rod with a paper towel to get a negative charge. Place the charged rods onto the rotating stands to show that unlike charges attract and like charges repel.
Be careful to use the correct paper towel when rubbing each rod, as shown in the photo above. The PVC (dark) rod uses the "-" towel. The Acrylic (clear) rod uses the "+" towel. Note that after each rod has been rubbed with the paper towel an equal and opposite charge will reside on the paper towel. So be sure to keep the towel away from the rod after it has been rubbed.
EQUIPMENT: Acrylic rods of sizes 12" and 24", PVC rods of sizes 12" and 24", rotating stands, paper towels marked "+" and "-".
SETUP NOTES: The rods are stored in the Electricity and Magnetism cabinets in the drawer marked "Static Electricity". Paper towels are in the dispenser by the sink. Mark each towel "+" and "-". The rotating stands are in a small cardboard box stored in the Electricity and Magnetism cabinets in the drawer marked "magnets".
Demo Notes:
Do NOT clean the acrylic rod with alcohol or water!! NEVER EVER USE ALCOHOL OR WATER TO CLEAN ACRYLIC! It will spontaneously crack without mercy and become destroyed. Use a dry or slightly damp paper towel to wipe the acrylic clean.
Hold the rods parallel to make them rotate with greater force, as shown in the photo below.
Hold the rods together parallel, with their surfaces held close together, as shown above.
Do not hold the rods together perpendicular, as shown below:
DO NOT HOLD THE RODS LIKE THIS. THEY WILL NOT HAVE A STRONG FORCE BECAUSE THEIR SURFACE AREAS ARE NOT CLOSE TOGETHER.
This demo can be done traditionally using cats fur and rubber, and shrink wrap plastic and glass. See the document titled Tribo_Trouble.doc for more details about the problems that occur with these materials due to moisture and skin oils.
REFERENCES:
Duane Roller and Duane H. D. Roller, The Prenatal History of Electrical Science, AJP 21,
343-356 (1953).
Robert C. Plumb, Triboelectricity, Journ. Chem. Ed. 48, 524, (1971).
D. S. Ainslie, What are the Essential conditions for Electrification by Rubbing?, AJP 35,
535-537, (1967).
Stanley Anderson, An Experiment to Demonstrate that "Friction" Electricity
Depends on Contact Potential,
AJP 144, (1936).Gilbert O. Spencer, Demonstrations in Electrostatics, AJP 26, 269, (1958).
Updated by Jun Qi in 3/9/2000