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Model No. ES-9080
Basic Electrostatics System
5
particularly humid day can cause charges to leak off any of the
apparatus, radically changing the charge distribution. To help
minimize leakage, keep all equipment free of dust and oil (e.g. from
fingerprints). On the other hand, a particularly dry day can cause
charge to easily build up in any moving object, including people.
Minimize all movement when demonstrating on a very dry day.
• Practice - Nothing can ruin the instructive value of a demonstration
more than failure due to a demonstrator’s unfamiliarity with the
equipment and procedure.
Before presenting a series of electrostatic demonstrations, the student
(and of course, the instructor) should be made aware of the following:
• The theory and use of the Faraday Ice Pail. (This is adequately
covered in the “Equipment Description” section and in
Demonstration 1.)
• The possible distortion of charge density due to improper use of the
proof plane. (See the “Equipment Description” section.)
• Residual charge may build up in the plastic insulator between the
handle and disk of the proof plane and charge producers. Make sure
to ground these parts before any experiment.
• The capacitance of the electrometer must be considered when
calculating the magnitude of a charge from the voltage reading of the
electrometer. (See Demonstration 3 for the procedure necessary to
determine the electrometer’s capacitance.)
By following the above principles and by practicing, the demonstrator
should have a high degree of success with the demonstrations and find
their educational effect of great value.
Equipment Description
Electrometer (ES-9078)
The Model ES-9078 Electrometer is a voltmeter used for direct
measurements of voltage and indirect measurements of current and
charge. Because of its high (“infinite”) impedance of 10
14
:
it is
especially suited for measuring charge in electrostatic experiments. It
has a sensitivity nearly 1000 times that of a standard gold-leaf
electroscope, a center-zero meter that directly indicates charge
polarity, and measures charges as low as 10
-11
coulombs.