We will perform two exercises designed to test your conceptual understanding of electric charge and electric force. Your lab notebook for this experiment should contain two separate back-to-back short reports.
Exercise 1: The Electroscope
These operations are referred to as "Sticky Tape Electrostatics" since you will be using Scotch Magic Tape to construct a low budget electroscope and to perform experiments that provide evidence for the following statements:
In your report, carefully document your experimental procedures and your line of reasoning that lead to each of the above conclusions.
You can find a description of suggested operations in another version of these experiments which can be found "on line" at the WWW server for the Science Exploratorium. Follow the instructions that are given there, but omit using the bent soda straws and supporting stands to hold the tape. Simply attach the tape "handles" to your fingertips.
For the instructions, point your browser at: Snackbook Experiments
Exercise 2: Electric Field Hockey
We will now try to develop a qualitative understanding of the Coulomb force and the
superposition of forces.
ELECTRIC FIELD HOCKEY is a computer-simulated game played with a charged puck (or "ball") on a frictionless surface. The object of the simulation, as in a traditional field hockey game, is to score a goal by propelling the puck into a net. However, here the puck is charged and moves only as a result of the influence of other charged particles which, once you put them where you want them, are "glued" down on the playing surface.
Since the game is a computer program, you can't run it on the WWW. You have to return to your computer's desktop and double-click on the shortcut icon: "Py Software". Then double-click on the folder called "Hockey", and finally double-click on "Hockey.bat".
Read the instructions about how the game works. Then do the following:
NOTE: To print your screen solution, first push the "Print Screen" key on the keyboard while the charge placements and trajectory are in view. This brings up the PrintKey menu. Click on the cropping tool (rectangular boxes). Click and drag over the region you wish to print. This copies the selected region to the clipboard. You can either print this region directly, or you can open the Microsoft Word processor, and "Paste" the contents of the clipboard into a document. Then print the document using the printer from the word processor.
In your discussion, answer these questions:
1) Suppose you changed the sign of the charges on the puck and on the fixed charges (turned all positive charges into negative and vice versa) for a situation where you scored a goal. What would be the effect on the trajectory of the puck? Explain.
2) How do the results of your "Level 0" trap simulations depend on the TWO DIMENSIONAL nature of Electric-Field Hockey? In other words, would it be possible to trap the puck using only fixed electric charges if the puck was moved perpendicularly out of the plane of the screen? Would the configurations that were able to trap the puck on the screen work in real life?