®
ES-9080B
012-07227G
Basic Electrostatics System
17
Demonstration 2: Charge Distribution
Equipment Setup
Introduction
The purpose of this demonstration is to investigate the way charge is distributed over a
surface by measuring variations of charge density. A charged surface will be sampled with a
proof plane. The proof plane will then be inserted in the Faraday Ice Pail to measure the
charge. By sampling different sections of the surface, the relative charge density can be
observed. For example, you may find that the amount of charge on two equal sized regions on
the surface of a conductor may differ in magnitude or even in sign. This occurs for non-
uniform charge distribution. Alternately, you may observe that everywhere on the surface the
charge has the same magnitude and sign. This occurs for uniform charge distribution.
An important aspect of measuring charge distributions is charge conservation. The proof
plane removes some charge from the surface it samples. If the proof plane is grounded after
each measurement, the surface will be depleted of charge with consecutive measurements.
Equipment Required:
Electrometer (ES-9078A)
Faraday Ice Pail (ES-9042A)
Electrostatic Voltage Source (ES-9077)
Proof Plane
Conductive Spheres, 13 cm (ES-9059B) (2)
Signal Input cable (Test leads)
Earth ground connection (patch cord)
Conductive Shapes (ES-9061)
Figure 2.1 Demonstration Setup
Charged
sphere
Sampling
sphere
Hollow
sphere
Conical
shape
