PASCO ES-9070, Instruction Manual And Experiment Manual

Page 1: ...012 03760E 05 99 1989 PASCO scientific 5 00 COULOMB BALANCE Instruction Manual and Experiment Guide for the PASCO scientific Model ES 9070 Includes Teacher s Notes and Typical Experiment Results ...

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Page 3: ...rn ii Introduction 1 Theory 2 Equipment 3 Additional Equipment Recommended 3 Tips for Accurate Results 4 Setup 5 Experiments Part A Force Versus Distance 7 Part B Force Versus Charge 8 Part C The Coulomb Constant 9 Replacing the Torsion Wire 13 Teacher s Guide 15 Technical Support Inside Back Cover ...

Page 4: ...alance manual is copyrighted and all rights reserved However permission is granted to non profit educational institutions for reproduction of any part of the manual providing the reproductions are used only for their laboratories and are not sold for profit Reproduction under any other circum stances without the written consent of PASCO scientific is prohibited Limited Warranty PASCO scientific wa...

Page 5: ...ire to twist The experimenter then twists the torsion wire to bring the balance back to its equilibrium position The angle through which the torsion wire must be twisted to reestablish equilibrium is directly proportional to the electrostatic force between the spheres All the variables of the Coulomb relationship F kq1 q2 R2 can be varied and measured using the Coulomb Balance You can verify the i...

Page 6: ...en the separated charges these free charges will move very quickly to reduce the field caused by the chargeseparation So since electrons and protons stick together with such tenacity onlyrelativelysmallchargedifferentialscanbe sustained in the laboratory This is so much the case that eventhoughtheelectrostaticforceismorethanabillion billion billion billiontimesasstrongasthegravitational force it t...

Page 7: ...it off whenever you are not chargingthespheres Figure 2 The Coulomb Balance chargingprobe slide assembly allen wrench for the slide assembly conductive sphere on insulating thread torsion wire clamp COULOMB BALANCE magnetic dampingarm index arm calibration supporttube toolboxwith one 50 mg mass two 20 mg masses one hex key torsion wire retainer pendulum coupling Plate spare torsion wire 3 meters ä...

Page 8: ...leeve cotton clothes are best and a grounding wire connected to theexperimenterishelpful Use a stable regulated kilovolt power supply to charge the spheres This will help ensure a constant chargethroughoutanexperiment When charging the spheres turn the power supply on charge the spheres then immediately turn the supply off The high voltage at the terminals of the supply can cause leakage currents ...

Page 9: ...alance and at the same height as the vane ä Important When storing the torsion balance always clamp the counterweight vane to protect the torsion wire When you do this be sure to adjust the height and angle of the index arm so that you can clamp the vane without pulling on the torsion wire Adjust the height of the magnetic damping arm so the counterweightvaneismidwaybetweenthemagnets Turn the tors...

Page 10: ...dex arm and the magnetic damping arm as needed to reestablish a horizontal relationship Align the spheres laterally by loosening the screw in the bottom of the slide assembly that anchors the vertical support rod for the sphere using the supplied allen wrench the vertical support rod must be moved to the end of the slide assembly touching the white plastic knob to access the screw Move the sphere ...

Page 11: ...necessary to balance the forces and bring the pendulum back to the zero position Record the distance R and the angle q in Table 1 Separate the spheres to their maximum separation recharge them to the same voltage then reposition the sliding sphere at a separation of 20 cm Measure the torsion angle and record your results again Repeat this measurement several times until your result is repeatable t...

Page 12: ...r data Calculate the correction factor B for each of the separations R that you used Record your results in Table 1 Multiply each of your collected values of q by 1 B and record your results as q corrected Reconstruct your graphs relating force and separation but this time use q corrected instead of q Make your new plot on the same graph as your original plot How does the correction factor affect ...

Page 13: ...gle of the degree plate in Table 2 Carefully place the 20 mg mass on the center line of the conductive sphere Turn the degree knob as required to bring the indexlinesbackintoalignment Readthetorsion angle on the degree scale Record the angle in Table 2 Repeat steps 3 and 4 using the two 20 mg masses and the 50 mg mass to apply each of the masses shown in the table Each time record the mass and the...

Page 14: ... q is touchedagainsttheicepail Sincethecapacitanceof the ice pail and electrometer is much greater than that of the sphere virtually all of the charge q is transferredontotheicepail Therelationship betweenthevoltagereadingoftheelectrometerand the charge deposited into the system is given by the equation q CV where C is the combined capaci tance of the electrometer the ice pail and the connecting l...

Page 15: ...e charge on the originalsphere onlyhalftheoriginalchargewastransferred Calculations for the Coulomb Constant The Coulomb constant can now be determined by using any data pair from your force versus distancedata Convert your torsion angle measurement qcorrected to a force measurement using your measured torsion constant for the torsion wire F Ktor qcorrected Determine the charge that was on the sph...

Page 16: ...Table 2 Force Calibration Data and Calculations Torsion constant Ktor B 1 4a3 R3 R q qavg qcorrected 1 R2 Table 1 Force versus Distance Data and Calculations C Capacitance of Electrometer System V ElectrometerVoltage q Charge on sphere 2CV Table 3 The Charge on the Sphere ...

Page 17: ...careful not to kink the wire As you thread the wire the end may become bent or kinked It will help to clip the end off so it remains straight Tighten the screws that hold the torsion wire gently Overtighteningwillbreakthewire The tension on the torsion wire is not a critical variable as long as the wire is reasonably taut The advantage of the spring balance is that it helps you adjust the tension ...

Page 18: ...n wrench 4 Thread the wire through the washer 3 a Remove the wire retainer by unscrewing it b Loosen the set screw and thumbscrew one full turn c Thread the wire in the direction shown d Retighten the set screw but do not tighten the thumb screw The wire must be able to turn Torsion wire 9 Adjust the height of the pendulum assem bly then tighten the set screws with the allen wrench 2 a Using the a...

Page 19: ... charge and show that force is linear with the other charge or you may charge both spheres equally and show that the force is proportional to the square of the charge The latter method is easier to control with a single voltage supply and was used for this write up J J J J J J J J J 0 20 40 60 80 100 120 0 1000 2000 3000 4000 5000 6000 Angle degrees Potential V f x 1 335407E 5 x 1 836206E 0 R 2 9 ...

Page 20: ...Notes 16 Coulomb Balance 012 03760D ...

Page 21: ...acting Technical Support Before you call the PASCO Technical Support staff it would be helpful to prepare the following information If your problem is with the PASCO apparatus note Title and model number usually listed on the label Approximate age of apparatus A detailed description of the problem sequence of events in case you can t call PASCO right away you won t lose valuable data If possible h...

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