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Unformatted text preview: Physics 2020 Lab: Charges and Electrostatics page 1 of 8 University of Colorado at Boulder, Department of Physics Lab: Charges and Electrostatics INTRODUCTION: Most modern applications of electricity involve electric charges in motion or current electricity. Historically, however, the first studies of electricity involved static charges, or electrostatics . You certainly feel the effects of electrostatic charges every time you touch a doorknob in the wintertime and get zapped. In this lab you will be introduced to an instrument called an electroscope , which is used to measure electric charge. By the end of this lab you should understand how the electroscope physically works, you should know how to use it to measure electric charge, and you should be able to use it as a tool to discover some electrical properties of various plastic materials. THE ELECTROSCOPE: The instrument that you will use in this lab is called an electroscope, shown in Figure 1. The electroscope consists of a metal ball connected by a metal rod (the stem ) to a very thin leaf of gold foil. The fragile part of the instrument is enclosed in a protective case. Electrons can flow freely within the ball, stem, and gold leaf. The leaf is very lightweight and floppy, so that an electrical repulsive force acting to lift it up can easily overcome the downward force of gravity. PRECAUTIONS & NOTES: Never tilt the electroscope or turn it upside down. This can t off. Just leave it on the table. When you bring a charged object near the electroscope, do so from the top. Do not bring any charged object near the glass sides, as this can twist the gold foil and rip it off. In order to ground the electroscope (that is, remove all the net charge from it so its neutral), touch the metal grounding plate to the metal ball on top of the electroscope. Touching your hand to the top of the electroscope can sometimes work, if you do not have any charge on your hands. Before charging and testing the plastic rods, make sure that they are neutral first. You can ground the plastic rods by covering the metal grounding plate with a damp towel and wipe the rods across the cloth. Always test the rod with the electroscope to make sure it is neutral first. If you rub two objects together to test the charge on each, make sure you hold the side that was rubbed near to the metal ball on the electroscope....
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