Lab III Coulomb Law

# Lab III Coulomb Law - Coulombs Law PHYS 296 Your name_...

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Coulomb’s Law PHYS 296 Your name___________ Lab section _______________ __ PRE-LAB QUIZZES 1. What is the purpose of this lab? 2. Two conducting hollow balls of radius 2.0 cm are both initially charged by a bias voltage of +5000 V. When they are brought to a center-to-center distance of 100.0 cm, what is the electrostatic force between them? Hint: see Lab 2 to calculate the net charge on each ball. 3. For the torsion balance, write down the relationship between the exerted force and the angle of rotation. 4. For the two conducting balls as described in problem 2, when one ball is attached to a torsion balance (as shown in Figure 1) the wire is twisted by a torsional angle of 1 ° . Assuming the length of the lever arm as 10.0 cm , find the torsion constant of the wire. Show the calculation.

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Coulomb’s Law PHYS 296 Name_ _________ Lab section _______________ __ Lab partner’s name(s)_____ ______ In this lab, we investigate the law governing the electrostatic force between electric charges. Purpose In 1785, Coulomb conducted a series of experiments investigating the electrostatic force between electric charges. Similar to Cavendish’s experimental approach in studying gravitational force, Coulomb employed a torsion balance to determine electrostatic force. As Coulomb discovered, the magnitude of the electrostatic force ( F ) between two charged objects, which are separated by a distance of r and bear electrical charges q 1 and q 2 , follows Equation (1): Background 2 2 1 r q q k F = , (1) where k = 9.0 × 10 9 N m 2 /C 2 . In this lab, we use the torsion balance as depicted in Figure 1 to measure electrostatic force and to verify Coulomb’s law. In this lab, the electrostatic force ( F ) is exerted on the conducting hollow ball with charge q 1 as shown in Figure 1 by a second conducting hollow ball of charge q 2 . The second ball is not shown in Figure 1 and can be moved along a sliding track to change the distance, r , between q 1 and q 2 . As shown, the first ball is attached to an insulation stick which is tightly fixed with the torsion wire. This way, the ball, the stick, and the wire rotate together under the electrostatic force which is exerted by the second ball and passes through the center of the first ball and along the perpendicular direction perpendicular to the wire. The force produces a torque on the wire described by FL T = , (2) where L is the lever arm, i.e., the distance between the center of the ball and the wire.
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## This note was uploaded on 06/03/2010 for the course PHYS 296 taught by Professor Staff during the Summer '08 term at University of Louisville.

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Lab III Coulomb Law - Coulombs Law PHYS 296 Your name_...

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