Basic Electrostatics System
ES-9080B
18
®
However, by not grounding the proof plane (and by not letting it touch the ice pail), the
charge on the surface is not depleted. That charge which the proof plane removed for one
measurement is always returned to the surface when the next sampling is made.
NOTE: When the disk of the proof plane touches the surface being sampled, it essentially becomes
part of the surface. To minimize distortion of the surface shape when sampling, hold the proof
plane flat against the surface, as indicated in the accessory instructions. Please refer to the
accessory instructions for details on how to use the proof planes.
Procedure:
1.
Before starting, make sure the Faraday Ice Pail is properly grounded, with the shield
connected to earth ground. The electrometer, connected to the pail, must also be grounded
(for example, when connected to the COM port on the electrostatics voltage source). Follow
the setup in Figure 2.1, with the black lead connected over the edge of the shield and the red
lead connected over the edge of the ice pail.
2.
Place the two conductive spheres at least 50 cm apart. Connect one of the spheres to the
+2000 VDC port on the Electrostatic Voltage Source (ES-9077). The voltage source
should be grounded to the same earth ground as the shield and the electrometer. (An earth
ground for the system is the AC adapter power supply for the Electrostatic Voltage
Source.) The connected sphere will be used as a charged body.
3.
Momentarily ground the other sphere to remove any residual charge from it.
4.
Start the demonstration by sampling and recording the charge at several different points on
the sampling sphere (the sphere that was grounded in step 2). Choose points on all sides to
represent an overall sample of the surface.
5.
Now bring the +2000 VDC charged sphere close to the grounded sphere, until their
surfaces are about 1 cm apart. Turn the voltage source ON, then sample and record the
charge at the same points sampled before.
6.
Momentarily ground the sampling sphere again, by touching one hand to the grounded ice
pail shield and the other hand to the sphere. (Make sure the ice pail is grounded before
doing this.) Again, sample and record the charge at the same points sampled before.
7.
Remove the +2000 VDC charged sphere until it is at least 50 cm away from the sampling
sphere. Again, sample and record the charge at the same points sampled before.
Analysis
1.
What produced the charge distributions at each step of the experiment?
2.
Why did any charge remain on the second sphere even after it was grounded?
