Instructor Side
JCE Classroom Activity: #5
Charge It! An Activity with Electricity by the Journal’s Editorial Staff
Background
perforated
fold here and tear out
Rubbing two objects together can cause electrons to be transferred from one object to another, producing a negative charge on one and a positive charge on the other. Rubbing plastic with hair, fur, or many types of cloth produces a negative charge on the plastic object. Rubbing a glass rod with silk produces a positive charge on the glass rod. Video examples of similar experiments are included in ChemDemos Videodisc (1) and Chemistry Comes Alive!, Volume 1 (2). A historic example is found in this issue of the Journal (3).
Integrating the Activity into Your Curriculum Use this activity to introduce the notion of positive and negative electric charge. This is appropriate when studying atomic theory, and when introducing electrochemistry. An important application of static electric charge is xerography, which is the basis for photocopiers and laser printers (see (4) and (5) under More Information below).
About the Activity This activity has been designed to be done in the classroom or at home. The objects required are common and readily available in most homes with the possible exception of the glass rod and silk, which the instructor may need to provide. Part 1. Running a plastic comb through your hair gives the comb a negative charge. The charged comb attracts a narrow stream of water, bending it toward the comb. The nearer the comb to the water, and the greater the charge (the more times the hair is combed) the greater the amount of bending seen. When the comb enters the water stream, the charge is dissipated and the comb no longer attracts the water. Part 2. Rubbing the comb with cloth will produce a similar effect. Some types of cloth will produce the effect to a greater degree. Other items made of plastic or glass will exhibit similar effects when rubbed with hair or cloth. A wooden pencil or metal letter opener will not be charged by rubbing with cloth. Both positive and negatively charged items will attract the stream of water. It is not possible to distinguish the sign of the charge based on this experiment. Part 3. The ball is initially attracted to both positive and negative charges. When it is touched by the charged object, it becomes charged and is now repelled by the object that touched it and by other objects of the same charge, and attracted to objects of opposite charge. With careful observation students should reach the conclusion that the comb and glass rod have opposite charges.
Questions 1. What happens (at the macroscopic level) to the comb when you run it through your hair? Electrons from the hair are transferred to the comb, producing a negative charge.
2. Do your experiments in Part 3 suggest the existence of more than one kind of electricity? Which objects display each type? By observing behavior in Part 3 students should be able to identify two types of charge and to classify charges as alike or different. They will not be able to determine which is positive and which is negative. These distinctions are arbitrary and have been established by definition.
More Information 1. Moore, J. W.; Jacobsen, J. J.; Hunsberger, L. R.; Gammon, S. D.; Jetzer, K. H.; Zimmerman, J. ChemDemos Videodisc. J. Chem. Educ. Software, 1994, SP 8. 2. Jacobsen, J. J.; Moore, J. W. Chemistry Comes Alive!, Volume 1, J. Chem. Educ. Software, 1997, SP 18 (in press). 3. Schatz, P. F. Anniversaries: 1998. J. Chem. Educ. 1998, 75, 23. 4. http://www.rankxerox.co.uk/info/howtocopy.html 5. http://www.physics.udel.edu/wwwusers/watson/scen167/xerox/
This Activity Sheet may be reproduced for use in the subscriber’s classroom. JChemEd.chem.wisc.edu • Vol. 75 No. 1 January 1998 • Journal of Chemical Education
80A
JCE Classroom Activity: #5
Student Side
Charge It! An Activity with Electricity by the Journal’s Editorial Staff About 300 years ago, Charles du Fay studied electrical charge. He charged glass and resin rods by rubbing them with silk, then touched them to various objects and observed the effect. From his studies he was able to identify two kinds of electricity. He called these vitreous electricity and resinous electricity. You can see the kinds of effects du Fay studied using common household items. Can you identify two kinds of electricity?
Try This
perforated
Part 1. You will need an inexpensive plastic comb (not coated with an anti-static film), a water faucet, a paper towel, and hair (hair on your head) or a piece of fur. Be sure to record all your observations. (Environmental Note: use cold water to avoid wasting energy; turn off the faucet between experiments to avoid wasting water.) __ 1. Turn on a water faucet so that a small but steady stream of water flows out. It should be no more than 1 or 2 mm in diameter, but should be steady, not drippy. __ 2. Hold the teeth of the comb close to the water stream. Move the comb so that it is a few millimeters from the stream, but not into the stream. What happens? __ 3. Comb through your hair (or fur sample) several times. Repeat step 2. Is there any change? Be sure to keep the comb out of the water! (The hair or fur must be dry and not oily for this to work well.) __ 4. Now place the comb in the water stream, and move it back to the position of step 2. What happens? __ 5. Dry the comb carefully and repeat step 3. Does the strength of the effect vary with the distance you hold the comb from the water stream? Does it depend on the number of times the hair is combed? Try combing through your hair 1 time, 3 times, and 10 times. Part 2. For the next set of experiments you will also need a small samples several types of cloth (cotton, wool, silk, polyester, nylon, etc.), a glass rod, and other small oblong objects made of various materials such as plastic spoon, a plastic cased pen, a wooden pencil, a metal letter opener or nail file, etc. __ 6. Rub each of the objects with your hair or fur and hold them near the water stream. Do any of them produce the same effect as the comb? __ 7. Rub the comb with each of the cloth samples and hold it near the water stream. Do any of these produce the same affect as when you combed through your hair? __ 8. Try each of the objects rubbed with the cloth samples. Rub vigorously for at least one minute. What combinations effect the stream of water?
Questions __1. What happens (at the atomic scale) to the comb when you run it through your hair? __2. Do your experiments in Part 3 suggest the existence of more than one kind of electricity? Explain.
Information from the World Wide Web 1. 2. 3. 4. 5.
http://library.advanced.org/12632/electricity/ http://www.clarityconnect.com/webpages/justjillw/pvsci/staticmachinepage.html http://theory.uwinnipeg.ca/physics/charge/node2.html http://www-spof.gsfc.nasa.gov/Education/welect.html http://buphy.bu.edu/py106/notes/Charge.html
This Activity Sheet may be reproduced for use in the subscriber’s classroom. 80B
Journal of Chemical Education • Vol. 75 No. 1 January 1998 • JChemEd.chem.wisc.edu
fold here and tear out
Part 3. For the next set of experiments you will need the plastic comb, hair or fur, a glass rod, a piece of silk cloth, aluminum foil, some string or thread, tape, and a table. You will need a partner for the final step. __ 9. Tape one end of a piece of string (about 8 to 10 inches) to a corner of a piece of aluminum foil (about 1 square foot). Crumple the foil into a ball about the diameter of a ping-pong ball around the taped string. Tape the other end of the string to the edge of a table so that the ball is suspended in the air. __ 10. Comb through your hair several times. Hold the teeth of the comb near the aluminum ball. Do not allow the comb to touch the ball. What happens? Touch the comb to the surface of the ball. Now what happens? __ 11. Repeat step 10 using a glass rod that has been rubbed vigorously for at least 1 minute with a piece of silk cloth. __ 12. Repeat step 10, then immediately replace the comb with the freshly silk-rubbed glass rod. What happens? You may need to repeat this step several times to be sure of the effect. Hold the ball in your hand for several seconds between trials so that it stands still for the next trial.
