2LB_Lab_5_CoulombsLaw6 - Coulombs Law (Pre lab Assignment...

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Coulomb’s Law (Pre lab Assignment Included) Objectives: The electric force acts between two charges or two charged objects. In contrast to mechanical forces, it acts even though there is nothing connecting the two charges. The value of the force and its dependence on distance is given by Coulomb’s law. The electrostatic force between two isolated point charges is described by Coulomb's Law . 2 12 2 1 r q q k F = This force between two charges can be measured directly with a torsion balance in a manner similar to Coulomb's original torsion balance measurements. In this lab we will measure the dependence of the force: (i) On charge q (ii) The the distance r 12 between the charges. NOTE: Given the nature of this experiment, it is best to avoid wearing clothing that contains polyester. Better measurements can be obtained by wearing fabrics containing cotton. Apparatus - The apparatus consists of the basic Coulomb's Law setup from Pasco : Zero knob Movable charged sphere Torsion Balance with One Charged sphere High voltage supply for charging spheres Probe 1. Torsion balance apparatus with two conducting spheres, calibrated distance scale, etc. 2. High voltage power supply (0-6 kV D.C.) with high impedance charging probe. 3. A Computer with Data Studio software is used to display and analyze data.
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The Physics - Coulomb's Law, expressed in SI units, is 2 12 2 1 0 4 1 r q q F πε = , where F is the force in Newtons, q 1 and q 2 are the charges in Coulombs, and r 12 is the distance between the point charges in meters. The constant ε 0 = 8.85 x 10 -12 C 2 / N m 2 makes the units and numbers work out right in the SI system. Coulomb's Law in terms of voltages In this lab each conducting sphere will be charged to a fixed voltage . This is completely equivalent to applying a fixed amount of charge. However, the data will be in terms of voltage , not charge . If positive voltages are applied, electrons are removed from the spheres by the voltages supply. If negative voltages are applied electrons are added to the spheres by the voltages supply. Note that electrons are the only one kind of charge that can be added or removed. The charging of the sphere is done by touching the spheres with the probe attached to the voltage supply.
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This note was uploaded on 01/11/2010 for the course PHYS 2b taught by Professor Clare during the Fall '07 term at UC Riverside.

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2LB_Lab_5_CoulombsLaw6 - Coulombs Law (Pre lab Assignment...

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