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Microsoft_PowerPoint___ES1ES2158intro

Microsoft_PowerPoint___ES1ES2158intro - ES1/ES2...

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ES1/ES2 Electrostatics In this lab you will explore several aspects of electrostatics such as charging by induction, distribution of charges on conductors etc. The basic tool for measuring charges is the electrometer which is a voltmeter with a very high input resistance. The principle is shown in the figure. To measure the charge q on the plates of the capacitor C, all we have to do is to determine the voltage V across its plates. The charge q is given by: Thus the charges we measure using this method are proportional to the electrometer reading. (page 1) C electrometer V +q - q q CV =

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electrometer + - + + + - - - - - - - + + + + pail shield Proof plane ground The capacitor we use is known as the “Faraday pail”. It consists of an inner and an outer can known as “pail”, and “shield”, respectively. If we introduce a positive charge +q inside the pail this induces charges –q and +q on the inner and outer surfaces of the pail. A charge –q is also induced on the inner surface of the shield. A positive charge +q on the outer surface of the shield escaped to the ground Please note the charge q can be determined in one of the following ways: 1. We can touch the proof plane on the bottom of the pail. In this case most of the charge on the proof plane is transferred to the pail. The electrometer will read even if we remove the proof plane 2. We can simply insert the proof plane inside the pail without touching the pail surface. In this case no charge is transferred to the pail. In this case the electrometer will read only as long as we keep the proof plain inside the pail. The electrometer will read zero when we remove the proof plane.
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