SE&M Activity III – D7: How Does a Soda can Show if it is Charged?

Name Group: Class Period:

	Earlier you discovered that charge on an insulator stays on the rubbed part of the surface. But when you shuffle ("rub") your feet on the carpet and grab a doorknob you feel the shock on your hand. How does the charge move from your feet to your hand? Do you think that you are an insulator or a conductor?
	Materials: Aluminum soda can, styrofoam cup, scotch magic tape, tinsel, acrylic sheet, styrofoam plate.
1. Tape the soda can to the bottom of an inverted styrofoam cup (see right). Then tape several pieces of tinsel to the end of the soda can (but not to the end with the opening). Make sure that each piece of tinsel is in contact with the can itself.
	2. Imagine rubbing an acrylic sheet with the styrofoam plate, then moving the styrofoam plate up and down against the soda can (but not where the tinsel is hanging). Predict what will happen to the tinsel pieces after the styrofoam plate is removed. Will they hang down or stick out?
	How did you decide?
	3. Test your prediction. Make sure the acrylic sheet is clean. Rub it vigorously against the styrofoam plate and then move the rubbed side of the styrofoam plate up and down against the end of the soda can, but not the end where the tinsel hangs. Make sure there is good contact between plate and can. After doing this for a few seconds, remove the plate. What happens to the pieces of tinsel?
	4. Most students find that the tinsel sticks out after the styrofoam is removed. If your tinsel does not stick out, discuss your situation with your instructor.
	5. In the previous activity the rubbed surface of a styrofoam plate was represented by a blue line. In the picture below, the styrofoam, the soda can, and the hanging tinsel are represented before the styrofoam is moved up and down against the can.
	6. Predict how you think the soda can, the styrofoam, and the tinsel should be colored, if at all, to represent the situation after the styrofoam is moved up and down against the soda can and then removed. To make your prediction, double-click on the picture below (Also use colored labels).
	How does your model support your prediction?
	7. Test your prediction. Open Act III-D7 Sim 1 and first take a picture of the initial set up and paste it in the space below.
	Initial Set Up
	Next, rub the charged insulator many times against the right side of the conductor then drag it back to the right end of the screen. The tinsel should be sticking out.
	8. To check your coloring prediction for the conductor, you need to turn ON the coloring scheme for the conductor. Double-click the conductor, and select "Model View.” This will turn on the coloring scheme. Click "OK". Take a picture of the final results and paste it below.
	Final Results
	9. Compare the thickness of the blue line on the insulator in the initial and final pictures above. How does your model of static electricity account for this? If it does not, don't you think it should?
	10. Compare coloring of the conductor and insulator with your predictions and try to resolve any differences in the coloring of the soda can or the coloring of the insulator before and after.
	11. Notice that the tinsel is colored blue. According to your model of static electricity, how did the tinsel become charged blue? Be sure to refer to relevant evidence such as that encountered in Activity III-D1.
	12. Why do you think the tinsel is sticking out, rather than just hanging straight down?
	13. Both the tinsel and the end of the aluminum can are charged blue. Therefore they will repel. Since the tinsel is so light, its end lifts up and points away from the end of the can. When the tinsel is observed to hang straight down we can infer that neither the tinsel nor the end of the can that the tinsel hangs from is charged. Since the tinsel sticks out when the soda can is charged, this apparatus can serve as a detector of charge. Such a detector is called an electroscope, in this case, a soda can electroscope.
	14. It is usually the case with your experimental apparatus that charge acquired by a conductor (or an insulator for that matter) doesn't remain for very long. Therefore, it is likely that your tinsel has dropped straight down by now. If so, make it stick out again by re-rubbing it with the acrylic-rubbed styrofoam. Then touch the can with your finger. Describe what happens to the tinsel.
	15. In terms of a MICROscopic model, what can you infer about the charge state of the soda can after you touched it?
	16. Return to the simulator. The conductor should be blue-charged and the tinsel should be sticking out. The simulator has a grounding hand tool located on the upper right of the Elements Palette. When you click on it the cursor will turn into a hand, use this to click on the conductor. What happens to the tinsel and to the coloring of the can?
	17. The process of causing the tinsel to go down by touching the conductor with your finger is called "grounding" the conductor. This removes all the excess charge from the conductor. In the next Cycle you will develop an explanation for why this happens. For now, just note that we can always make a charged conductor become uncharged by grounding it with our finger.
	18. Imagine rubbing the uncharged can with the rubbed acrylic plate instead of the styrofoam plate. Predict what you think would happen by coloring in all the objects below in the “Before” and “After” pictures. Double click on them and use the drawing tools.
	How does your model support your prediction?
	19. To test your prediction, open Act III-D7 Sim2. Take a picture of the initial set-up and paste it below for comparison (Label the charged sides R or B).
	Drag the charged insulator over to the conductor and rub it many times. Then drag the insulator back to the right part of the screen, the tinsel should be sticking out. Turn ON the coloring scheme (model view) for the conductor (instructions are given above in step 8). Take a picture of the final coloring and paste it below.
	20. How does the coloring scheme in the simulator pictures compare with your predictions? Try to resolve any differences.
	21. Go to your Cycle III Idea Journal. Based on evidence gathered in this activity, write a statement about charging a conductor by rubbing. You should also make some statements about some of the differences you have noticed between insulators and conductors with respect to charge. Also, update your MICROscopic model of static electricity if necessary.