012–07227A
Basic Electrostatics System
7
Here are some guidelines in the proper use and care of the charge producers that are
important to remember:
• If a zero charge is desirable, discharge the charge producers by touching the conductive disk to ground. To
be sure the disk is fully discharged, gently breathe on the non conductive neck. The moisture from your
breath will help remove any stray charge.
• Avoid touching the neck during normal use. The oils from your hands will provide a path for charges to leak
off. If you experience a lot of leakage, wash the white insulator shafts with soap and water rinsing
generously, the leakage should disappear. Occasionally clean the disk surfaces with alcohol.
• When you first use the charge producers, or just after cleaning, they may not produce charges readily. Rub
the white surface vigorously on the conductive proof plane disk.
• The charge producers are designed to be used with the electrometer ES-9078. They do not produce sufficient
charge for use with a standard electroscope.
The Proof Plane
As shown in Figure 8, the proof plane is an aluminum-
covered conductive disk attached to an insulated handle. The
conductive disk material is carbon-filled black polycarbonate
(about 10
3
Ω
) with an aluminum disk. The nonconductive
neck is white polycarbonate (about 10
14
Ω
).
The Proof plane is used to sample the charge density on
charged conductive surfaces. A Faraday Ice Pail can then be
used to measure the charge density on the proof plane.
By touching the proof plane to a surface, the proof plane will
acquire the same charge distribution as the section of the surface
it touched (see Figure 9). By measuring the charge on the proof
plane, the charge density on that part of the surface can be
determined. The greater the charge on the proof plane, the greater
the charge density on the surface where the proof plane made
contact.
When a proof plane is touched to a conductive surface, the proof
plane becomes part of the conductive surface. If the effect on the
shape of the surface is significant, the sampling of the charge
density will not be accurate. Therefore, always touch the proof
plane to the conductor in such a way as to minimize the distortion
of the shape of the surface. Figure 10 shows the recommended
method for using the proof plane to sample the charge on a
conductive sphere.
Figure 8. Proof Plane
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
Figure 9. Proof Planes removing
charge
area
sampled
charge in proof
plane equals
charge of
sampled area
conductive disk
(black)
non-conductive
neck (white)
aluminum surface
handle