EM3_Manual

# EM3_Manual - General Physics II Lab EM3 Coulomb Constant...

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General Physics II Lab EM3 Coulomb Constant General Physics II Lab EM3 Coulomb Constant Purpose In this experiment, you will use the Coulomb balance to determine the Coulomb constant k e . Equipment and components Coulomb balance, slide assembly, high voltage power supply, charging probe and grounding probe with holders, tweezers, milligram mass (50 mg (x1), 20 mg (x2)), acrylic transparent box to cover the whole setup, hair-blower, stand and clamp, stop watch, electrometer with battery box, BNC to crocodile clips cable, 4 mm plug to plug cable (for earth grounding), Faraday ice pail, and capacitance meter. Background Coulomb’s law states that the electric force between two point charges q 1 and q 2 at separation r is 12 e 2 qq k F r = , (1) where k e = 8.9875 × 10 9 N m 2 /C 2 is the Coulomb constant. This constant is also written in the form k e = 1/(4 πε 0 ), where ε 0 = 8.8542 × 10 -12 C 2 /N m 2 is known as the permittivity of free space. In Experiment EM1, you used the Coulomb balance to measure the electrostatic force F between two charged spheres as a function of their separation r and verified that F is proportional to 1/ r 2 . In this experiment, you will continue the study of Coulomb’s law and determine the value of the Coulomb constant k e in air. To accomplish this, you need to know the exact amount of charges carried by each conductive sphere and calibrate the Coulomb balance against a known force. Procedure I. Calibration of the torsion balance 1. Carefully turn the torsion balance on its side, supporting it with the lateral support bar, as shown in Figure 1. Place the support tube under the sphere, as shown. Figure 1 Calibration of the torsion balance Revised: 15 November 2010 1/8

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General Physics II Lab EM3 Coulomb Constant 2. Zero the torsion balance by rotating the torsion dial until the index lines are aligned. Record the angle θ of the degree plate in Table 1 in the lab report. 3. Carefully place a 20 mg mass on the center line of the conductive sphere. 4. Turn the degree knob to bring the index lines back into alignment. Read the torsion angle on the degree scale. Record the angle in Table 1. 5. Repeat steps 3 and 4, using a combination of two 20 mg masses and a 50 mg mass to apply each of the masses listed in Table 1. Each time record the mass and the torsion angle θ .
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EM3_Manual - General Physics II Lab EM3 Coulomb Constant...

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